| 1 | |
| 2 | |
| 3 | * Fast Userspace Mutexes (which I call "Futexes!").
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| 4 | * (C) Rusty Russell, IBM 2002
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| 5 | *
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| 6 | * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
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| 7 | * (C) Copyright 2003 Red Hat Inc, All Rights Reserved
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| 8 | *
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| 9 | * Removed page pinning, fix privately mapped COW pages and other cleanups
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| 10 | * (C) Copyright 2003, 2004 Jamie Lokier
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| 11 | *
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| 12 | * Robust futex support started by Ingo Molnar
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| 13 | * (C) Copyright 2006 Red Hat Inc, All Rights Reserved
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| 14 | * Thanks to Thomas Gleixner for suggestions, analysis and fixes.
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| 15 | *
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| 16 | * PI-futex support started by Ingo Molnar and Thomas Gleixner
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| 17 | * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <[email protected]>
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| 18 | * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <[email protected]>
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| 19 | *
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| 20 | * PRIVATE futexes by Eric Dumazet
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| 21 | * Copyright (C) 2007 Eric Dumazet <[email protected]>
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| 22 | *
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| 23 | * Requeue-PI support by Darren Hart <[email protected]>
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| 24 | * Copyright (C) IBM Corporation, 2009
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| 25 | * Thanks to Thomas Gleixner for conceptual design and careful reviews.
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| 26 | *
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| 27 | * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
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| 28 | * enough at me, Linus for the original (flawed) idea, Matthew
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| 29 | * Kirkwood for proof-of-concept implementation.
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| 30 | *
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| 31 | * "The futexes are also cursed."
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| 32 | * "But they come in a choice of three flavours!"
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| 33 |
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| 34 | #include <linux/compat.h>
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| 35 | #include <linux/slab.h>
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| 36 | #include <linux/poll.h>
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| 37 | #include <linux/fs.h>
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| 38 | #include <linux/file.h>
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| 39 | #include <linux/jhash.h>
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| 40 | #include <linux/init.h>
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| 41 | #include <linux/futex.h>
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| 42 | #include <linux/mount.h>
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| 43 | #include <linux/pagemap.h>
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| 44 | #include <linux/syscalls.h>
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| 45 | #include <linux/signal.h>
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| 46 | #include <linux/export.h>
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| 47 | #include <linux/magic.h>
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| 48 | #include <linux/pid.h>
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| 49 | #include <linux/nsproxy.h>
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| 50 | #include <linux/ptrace.h>
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| 51 | #include <linux/sched/rt.h>
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| 52 | #include <linux/sched/wake_q.h>
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| 53 | #include <linux/sched/mm.h>
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| 54 | #include <linux/hugetlb.h>
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| 55 | #include <linux/freezer.h>
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| 56 | #include <linux/memblock.h>
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| 57 | #include <linux/fault-inject.h>
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| 58 | #include <linux/refcount.h>
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| 59 |
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| 60 | #include <asm/futex.h>
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| 61 |
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| 62 | #include "locking/rtmutex_common.h"
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| 63 |
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| 64 | |
| 65 | * READ this before attempting to hack on futexes!
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| 66 | *
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| 67 | * Basic futex operation and ordering guarantees
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| 68 | * =============================================
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| 69 | *
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| 70 | * The waiter reads the futex value in user space and calls
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| 71 | * futex_wait(). This function computes the hash bucket and acquires
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| 72 | * the hash bucket lock. After that it reads the futex user space value
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| 73 | * again and verifies that the data has not changed. If it has not changed
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| 74 | * it enqueues itself into the hash bucket, releases the hash bucket lock
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| 75 | * and schedules.
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| 76 | *
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| 77 | * The waker side modifies the user space value of the futex and calls
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| 78 | * futex_wake(). This function computes the hash bucket and acquires the
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| 79 | * hash bucket lock. Then it looks for waiters on that futex in the hash
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| 80 | * bucket and wakes them.
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| 81 | *
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| 82 | * In futex wake up scenarios where no tasks are blocked on a futex, taking
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| 83 | * the hb spinlock can be avoided and simply return. In order for this
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| 84 | * optimization to work, ordering guarantees must exist so that the waiter
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| 85 | * being added to the list is acknowledged when the list is concurrently being
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| 86 | * checked by the waker, avoiding scenarios like the following:
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| 87 | *
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| 88 | * CPU 0 CPU 1
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| 89 | * val = *futex;
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| 90 | * sys_futex(WAIT, futex, val);
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| 91 | * futex_wait(futex, val);
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| 92 | * uval = *futex;
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| 93 | * *futex = newval;
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| 94 | * sys_futex(WAKE, futex);
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| 95 | * futex_wake(futex);
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| 96 | * if (queue_empty())
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| 97 | * return;
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| 98 | * if (uval == val)
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| 99 | * lock(hash_bucket(futex));
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| 100 | * queue();
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| 101 | * unlock(hash_bucket(futex));
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| 102 | * schedule();
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| 103 | *
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| 104 | * This would cause the waiter on CPU 0 to wait forever because it
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| 105 | * missed the transition of the user space value from val to newval
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| 106 | * and the waker did not find the waiter in the hash bucket queue.
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| 107 | *
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| 108 | * The correct serialization ensures that a waiter either observes
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| 109 | * the changed user space value before blocking or is woken by a
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| 110 | * concurrent waker:
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| 111 | *
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| 112 | * CPU 0 CPU 1
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| 113 | * val = *futex;
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| 114 | * sys_futex(WAIT, futex, val);
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| 115 | * futex_wait(futex, val);
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| 116 | *
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| 117 | * waiters++; (a)
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| 118 | * smp_mb(); (A) <-- paired with -.
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| 119 | * |
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| 120 | * lock(hash_bucket(futex)); |
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| 121 | * |
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| 122 | * uval = *futex; |
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| 123 | * | *futex = newval;
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| 124 | * | sys_futex(WAKE, futex);
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| 125 | * | futex_wake(futex);
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| 126 | * |
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| 127 | * `--------> smp_mb(); (B)
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| 128 | * if (uval == val)
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| 129 | * queue();
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| 130 | * unlock(hash_bucket(futex));
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| 131 | * schedule(); if (waiters)
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| 132 | * lock(hash_bucket(futex));
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| 133 | * else wake_waiters(futex);
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| 134 | * waiters--; (b) unlock(hash_bucket(futex));
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| 135 | *
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| 136 | * Where (A) orders the waiters increment and the futex value read through
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| 137 | * atomic operations (see hb_waiters_inc) and where (B) orders the write
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| 138 | * to futex and the waiters read (see hb_waiters_pending()).
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| 139 | *
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| 140 | * This yields the following case (where X:=waiters, Y:=futex):
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| 141 | *
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| 142 | * X = Y = 0
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| 143 | *
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| 144 | * w[X]=1 w[Y]=1
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| 145 | * MB MB
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| 146 | * r[Y]=y r[X]=x
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| 147 | *
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| 148 | * Which guarantees that x==0 && y==0 is impossible; which translates back into
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| 149 | * the guarantee that we cannot both miss the futex variable change and the
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| 150 | * enqueue.
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| 151 | *
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| 152 | * Note that a new waiter is accounted for in (a) even when it is possible that
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| 153 | * the wait call can return error, in which case we backtrack from it in (b).
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| 154 | * Refer to the comment in queue_lock().
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| 155 | *
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| 156 | * Similarly, in order to account for waiters being requeued on another
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| 157 | * address we always increment the waiters for the destination bucket before
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| 158 | * acquiring the lock. It then decrements them again after releasing it -
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| 159 | * the code that actually moves the futex(es) between hash buckets (requeue_futex)
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| 160 | * will do the additional required waiter count housekeeping. This is done for
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| 161 | * double_lock_hb() and double_unlock_hb(), respectively.
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| 162 |
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| 163 |
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| 164 | #ifdef CONFIG_HAVE_FUTEX_CMPXCHG
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| 165 | #define futex_cmpxchg_enabled 1
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| 166 | #else
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| 167 | static int __read_mostly futex_cmpxchg_enabled;
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| 168 | #endif
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| 169 |
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| 170 | |
| 171 | * Futex flags used to encode options to functions and preserve them across
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| 172 | * restarts.
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| 173 |
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| 174 | #ifdef CONFIG_MMU
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| 175 | # define FLAGS_SHARED 0x01
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| 176 | #else
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| 177 | |
| 178 | * NOMMU does not have per process address space. Let the compiler optimize
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| 179 | * code away.
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| 180 |
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| 181 | # define FLAGS_SHARED 0x00
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| 182 | #endif
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| 183 | #define FLAGS_CLOCKRT 0x02
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| 184 | #define FLAGS_HAS_TIMEOUT 0x04
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| 185 |
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| 186 | |
| 187 | * Priority Inheritance state:
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| 188 |
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| 189 | struct futex_pi_state {
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| 190 | |
| 191 | * list of 'owned' pi_state instances - these have to be
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| 192 | * cleaned up in do_exit() if the task exits prematurely:
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| 193 |
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| 194 | struct list_head list;
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| 195 |
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| 196 | |
| 197 | * The PI object:
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| 198 |
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| 199 | struct rt_mutex pi_mutex;
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| 200 |
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| 201 | struct task_struct *owner;
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| 202 | refcount_t refcount;
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| 203 |
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| 204 | union futex_key key;
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| 205 | } __randomize_layout;
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| 206 |
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| 207 | |
| 208 | * struct futex_q - The hashed futex queue entry, one per waiting task
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| 209 | * @list: priority-sorted list of tasks waiting on this futex
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| 210 | * @task: the task waiting on the futex
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| 211 | * @lock_ptr: the hash bucket lock
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| 212 | * @key: the key the futex is hashed on
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| 213 | * @pi_state: optional priority inheritance state
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| 214 | * @rt_waiter: rt_waiter storage for use with requeue_pi
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| 215 | * @requeue_pi_key: the requeue_pi target futex key
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| 216 | * @bitset: bitset for the optional bitmasked wakeup
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| 217 | *
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| 218 | * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so
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| 219 | * we can wake only the relevant ones (hashed queues may be shared).
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| 220 | *
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| 221 | * A futex_q has a woken state, just like tasks have TASK_RUNNING.
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| 222 | * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
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| 223 | * The order of wakeup is always to make the first condition true, then
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| 224 | * the second.
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| 225 | *
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| 226 | * PI futexes are typically woken before they are removed from the hash list via
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| 227 | * the rt_mutex code. See unqueue_me_pi().
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| 228 |
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| 229 | struct futex_q {
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| 230 | struct plist_node list;
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| 231 |
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| 232 | struct task_struct *task;
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| 233 | spinlock_t *lock_ptr;
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| 234 | union futex_key key;
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| 235 | struct futex_pi_state *pi_state;
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| 236 | struct rt_mutex_waiter *rt_waiter;
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| 237 | union futex_key *requeue_pi_key;
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| 238 | u32 bitset;
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| 239 | } __randomize_layout;
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| 240 |
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| 241 | static const struct futex_q futex_q_init = {
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| 242 |
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| 243 | .key = FUTEX_KEY_INIT,
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| 244 | .bitset = FUTEX_BITSET_MATCH_ANY
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| 245 | };
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| 246 |
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| 247 | |
| 248 | * Hash buckets are shared by all the futex_keys that hash to the same
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| 249 | * location. Each key may have multiple futex_q structures, one for each task
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| 250 | * waiting on a futex.
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| 251 |
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| 252 | struct futex_hash_bucket {
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| 253 | atomic_t waiters;
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| 254 | spinlock_t lock;
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| 255 | struct plist_head chain;
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| 256 | } ____cacheline_aligned_in_smp;
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| 257 |
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| 258 | |
| 259 | * The base of the bucket array and its size are always used together
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| 260 | * (after initialization only in hash_futex()), so ensure that they
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| 261 | * reside in the same cacheline.
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| 262 |
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| 263 | static struct {
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| 264 | struct futex_hash_bucket *queues;
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| 265 | unsigned long hashsize;
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| 266 | } __futex_data __read_mostly __aligned(2*sizeof(long));
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| 267 | #define futex_queues (__futex_data.queues)
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| 268 | #define futex_hashsize (__futex_data.hashsize)
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| 269 |
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| 270 |
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| 271 | |
| 272 | * Fault injections for futexes.
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| 273 |
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| 274 | #ifdef CONFIG_FAIL_FUTEX
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| 275 |
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| 276 | static struct {
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| 277 | struct fault_attr attr;
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| 278 |
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| 279 | bool ignore_private;
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| 280 | } fail_futex = {
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| 281 | .attr = FAULT_ATTR_INITIALIZER,
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| 282 | .ignore_private = false,
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| 283 | };
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| 284 |
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| 285 | static int __init setup_fail_futex(char *str)
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| 286 | {
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| 287 | return setup_fault_attr(&fail_futex.attr, str);
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| 288 | }
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| 289 | __setup("fail_futex=", setup_fail_futex);
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| 290 |
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| 291 | static bool should_fail_futex(bool fshared)
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| 292 | {
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| 293 | if (fail_futex.ignore_private && !fshared)
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| 294 | return false;
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| 295 |
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| 296 | return should_fail(&fail_futex.attr, 1);
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| 297 | }
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| 298 |
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| 299 | #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
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| 300 |
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| 301 | static int __init fail_futex_debugfs(void)
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| 302 | {
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| 303 | umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
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| 304 | struct dentry *dir;
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| 305 |
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| 306 | dir = fault_create_debugfs_attr("fail_futex", NULL,
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| 307 | &fail_futex.attr);
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| 308 | if (IS_ERR(dir))
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| 309 | return PTR_ERR(dir);
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| 310 |
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| 311 | debugfs_create_bool("ignore-private", mode, dir,
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| 312 | &fail_futex.ignore_private);
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| 313 | return 0;
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| 314 | }
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| 315 |
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| 316 | late_initcall(fail_futex_debugfs);
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| 317 |
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| 318 | #endif
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| 319 |
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| 320 | #else
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| 321 | static inline bool should_fail_futex(bool fshared)
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| 322 | {
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| 323 | return false;
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| 324 | }
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| 325 | #endif
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| 326 |
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| 327 | #ifdef CONFIG_COMPAT
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| 328 | static void compat_exit_robust_list(struct task_struct *curr);
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| 329 | #else
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| 330 | static inline void compat_exit_robust_list(struct task_struct *curr) { }
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| 331 | #endif
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| 332 |
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| 333 | |
| 334 | * Reflects a new waiter being added to the waitqueue.
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| 335 |
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| 336 | static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
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| 337 | {
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| 338 | #ifdef CONFIG_SMP
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| 339 | atomic_inc(&hb->waiters);
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| 340 | |
| 341 | * Full barrier (A), see the ordering comment above.
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| 342 |
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| 343 | smp_mb__after_atomic();
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| 344 | #endif
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| 345 | }
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| 346 |
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| 347 | |
| 348 | * Reflects a waiter being removed from the waitqueue by wakeup
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| 349 | * paths.
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| 350 |
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| 351 | static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
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| 352 | {
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| 353 | #ifdef CONFIG_SMP
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| 354 | atomic_dec(&hb->waiters);
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| 355 | #endif
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| 356 | }
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| 357 |
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| 358 | static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
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| 359 | {
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| 360 | #ifdef CONFIG_SMP
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| 361 | |
| 362 | * Full barrier (B), see the ordering comment above.
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| 363 |
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| 364 | smp_mb();
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| 365 | return atomic_read(&hb->waiters);
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| 366 | #else
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| 367 | return 1;
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| 368 | #endif
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| 369 | }
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| 370 |
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| 371 | |
| 372 | * hash_futex - Return the hash bucket in the global hash
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| 373 | * @key: Pointer to the futex key for which the hash is calculated
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| 374 | *
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| 375 | * We hash on the keys returned from get_futex_key (see below) and return the
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| 376 | * corresponding hash bucket in the global hash.
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| 377 |
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| 378 | static struct futex_hash_bucket *hash_futex(union futex_key *key)
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| 379 | {
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| 380 | u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
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| 381 | key->both.offset);
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| 382 |
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| 383 | return &futex_queues[hash & (futex_hashsize - 1)];
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| 384 | }
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| 385 |
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| 386 |
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| 387 | |
| 388 | * match_futex - Check whether two futex keys are equal
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| 389 | * @key1: Pointer to key1
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| 390 | * @key2: Pointer to key2
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| 391 | *
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| 392 | * Return 1 if two futex_keys are equal, 0 otherwise.
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| 393 |
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| 394 | static inline int match_futex(union futex_key *key1, union futex_key *key2)
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| 395 | {
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| 396 | return (key1 && key2
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| 397 | && key1->both.word == key2->both.word
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| 398 | && key1->both.ptr == key2->both.ptr
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| 399 | && key1->both.offset == key2->both.offset);
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| 400 | }
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| 401 |
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| 402 | enum futex_access {
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| 403 | FUTEX_READ,
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| 404 | FUTEX_WRITE
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| 405 | };
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| 406 |
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| 407 | |
| 408 | * futex_setup_timer - set up the sleeping hrtimer.
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| 409 | * @time: ptr to the given timeout value
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| 410 | * @timeout: the hrtimer_sleeper structure to be set up
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| 411 | * @flags: futex flags
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| 412 | * @range_ns: optional range in ns
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| 413 | *
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| 414 | * Return: Initialized hrtimer_sleeper structure or NULL if no timeout
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| 415 | * value given
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| 416 |
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| 417 | static inline struct hrtimer_sleeper *
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| 418 | futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout,
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| 419 | int flags, u64 range_ns)
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| 420 | {
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| 421 | if (!time)
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| 422 | return NULL;
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| 423 |
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| 424 | hrtimer_init_sleeper_on_stack(timeout, (flags & FLAGS_CLOCKRT) ?
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| 425 | CLOCK_REALTIME : CLOCK_MONOTONIC,
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| 426 | HRTIMER_MODE_ABS);
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| 427 | |
| 428 | * If range_ns is 0, calling hrtimer_set_expires_range_ns() is
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| 429 | * effectively the same as calling hrtimer_set_expires().
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| 430 |
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| 431 | hrtimer_set_expires_range_ns(&timeout->timer, *time, range_ns);
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| 432 |
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| 433 | return timeout;
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| 434 | }
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| 435 |
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| 436 | |
| 437 | * Generate a machine wide unique identifier for this inode.
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| 438 | *
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| 439 | * This relies on u64 not wrapping in the life-time of the machine; which with
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| 440 | * 1ns resolution means almost 585 years.
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| 441 | *
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| 442 | * This further relies on the fact that a well formed program will not unmap
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| 443 | * the file while it has a (shared) futex waiting on it. This mapping will have
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| 444 | * a file reference which pins the mount and inode.
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| 445 | *
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| 446 | * If for some reason an inode gets evicted and read back in again, it will get
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| 447 | * a new sequence number and will _NOT_ match, even though it is the exact same
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| 448 | * file.
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| 449 | *
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| 450 | * It is important that match_futex() will never have a false-positive, esp.
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| 451 | * for PI futexes that can mess up the state. The above argues that false-negatives
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| 452 | * are only possible for malformed programs.
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| 453 |
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| 454 | static u64 get_inode_sequence_number(struct inode *inode)
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| 455 | {
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| 456 | static atomic64_t i_seq;
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| 457 | u64 old;
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| 458 |
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| 459 |
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| 460 | old = atomic64_read(&inode->i_sequence);
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| 461 | if (likely(old))
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| 462 | return old;
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| 463 |
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| 464 | for (;;) {
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| 465 | u64 new = atomic64_add_return(1, &i_seq);
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| 466 | if (WARN_ON_ONCE(!new))
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| 467 | continue;
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| 468 |
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| 469 | old = atomic64_cmpxchg_relaxed(&inode->i_sequence, 0, new);
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| 470 | if (old)
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| 471 | return old;
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| 472 | return new;
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| 473 | }
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| 474 | }
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| 475 |
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| 476 | |
| 477 | * get_futex_key() - Get parameters which are the keys for a futex
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| 478 | * @uaddr: virtual address of the futex
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| 479 | * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
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| 480 | * @key: address where result is stored.
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| 481 | * @rw: mapping needs to be read/write (values: FUTEX_READ,
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| 482 | * FUTEX_WRITE)
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| 483 | *
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| 484 | * Return: a negative error code or 0
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| 485 | *
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| 486 | * The key words are stored in @key on success.
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| 487 | *
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| 488 | * For shared mappings (when @fshared), the key is:
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| 489 | * ( inode->i_sequence, page->index, offset_within_page )
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| 490 | * [ also see get_inode_sequence_number() ]
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| 491 | *
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| 492 | * For private mappings (or when !@fshared), the key is:
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| 493 | * ( current->mm, address, 0 )
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| 494 | *
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| 495 | * This allows (cross process, where applicable) identification of the futex
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| 496 | * without keeping the page pinned for the duration of the FUTEX_WAIT.
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| 497 | *
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| 498 | * lock_page() might sleep, the caller should not hold a spinlock.
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| 499 |
|
| 500 | static int
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| 501 | get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, enum futex_access rw)
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| 502 | {
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| 503 | unsigned long address = (unsigned long)uaddr;
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| 504 | struct mm_struct *mm = current->mm;
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| 505 | struct page *page, *tail;
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| 506 | struct address_space *mapping;
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| 507 | int err, ro = 0;
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| 508 |
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| 509 | |
| 510 | * The futex address must be "naturally" aligned.
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| 511 |
|
| 512 | key->both.offset = address % PAGE_SIZE;
|
| 513 | if (unlikely((address % sizeof(u32)) != 0))
|
| 514 | return -EINVAL;
|
| 515 | address -= key->both.offset;
|
| 516 |
|
| 517 | if (unlikely(!access_ok(uaddr, sizeof(u32))))
|
| 518 | return -EFAULT;
|
| 519 |
|
| 520 | if (unlikely(should_fail_futex(fshared)))
|
| 521 | return -EFAULT;
|
| 522 |
|
| 523 | |
| 524 | * PROCESS_PRIVATE futexes are fast.
|
| 525 | * As the mm cannot disappear under us and the 'key' only needs
|
| 526 | * virtual address, we dont even have to find the underlying vma.
|
| 527 | * Note : We do have to check 'uaddr' is a valid user address,
|
| 528 | * but access_ok() should be faster than find_vma()
|
| 529 |
|
| 530 | if (!fshared) {
|
| 531 | key->private.mm = mm;
|
| 532 | key->private.address = address;
|
| 533 | return 0;
|
| 534 | }
|
| 535 |
|
| 536 | again:
|
| 537 |
|
| 538 | if (unlikely(should_fail_futex(fshared)))
|
| 539 | return -EFAULT;
|
| 540 |
|
| 541 | err = get_user_pages_fast(address, 1, FOLL_WRITE, &page);
|
| 542 | |
| 543 | * If write access is not required (eg. FUTEX_WAIT), try
|
| 544 | * and get read-only access.
|
| 545 |
|
| 546 | if (err == -EFAULT && rw == FUTEX_READ) {
|
| 547 | err = get_user_pages_fast(address, 1, 0, &page);
|
| 548 | ro = 1;
|
| 549 | }
|
| 550 | if (err < 0)
|
| 551 | return err;
|
| 552 | else
|
| 553 | err = 0;
|
| 554 |
|
| 555 | |
| 556 | * The treatment of mapping from this point on is critical. The page
|
| 557 | * lock protects many things but in this context the page lock
|
| 558 | * stabilizes mapping, prevents inode freeing in the shared
|
| 559 | * file-backed region case and guards against movement to swap cache.
|
| 560 | *
|
| 561 | * Strictly speaking the page lock is not needed in all cases being
|
| 562 | * considered here and page lock forces unnecessarily serialization
|
| 563 | * From this point on, mapping will be re-verified if necessary and
|
| 564 | * page lock will be acquired only if it is unavoidable
|
| 565 | *
|
| 566 | * Mapping checks require the head page for any compound page so the
|
| 567 | * head page and mapping is looked up now. For anonymous pages, it
|
| 568 | * does not matter if the page splits in the future as the key is
|
| 569 | * based on the address. For filesystem-backed pages, the tail is
|
| 570 | * required as the index of the page determines the key. For
|
| 571 | * base pages, there is no tail page and tail == page.
|
| 572 |
|
| 573 | tail = page;
|
| 574 | page = compound_head(page);
|
| 575 | mapping = READ_ONCE(page->mapping);
|
| 576 |
|
| 577 | |
| 578 | * If page->mapping is NULL, then it cannot be a PageAnon
|
| 579 | * page; but it might be the ZERO_PAGE or in the gate area or
|
| 580 | * in a special mapping (all cases which we are happy to fail);
|
| 581 | * or it may have been a good file page when get_user_pages_fast
|
| 582 | * found it, but truncated or holepunched or subjected to
|
| 583 | * invalidate_complete_page2 before we got the page lock (also
|
| 584 | * cases which we are happy to fail). And we hold a reference,
|
| 585 | * so refcount care in invalidate_complete_page's remove_mapping
|
| 586 | * prevents drop_caches from setting mapping to NULL beneath us.
|
| 587 | *
|
| 588 | * The case we do have to guard against is when memory pressure made
|
| 589 | * shmem_writepage move it from filecache to swapcache beneath us:
|
| 590 | * an unlikely race, but we do need to retry for page->mapping.
|
| 591 |
|
| 592 | if (unlikely(!mapping)) {
|
| 593 | int shmem_swizzled;
|
| 594 |
|
| 595 | |
| 596 | * Page lock is required to identify which special case above
|
| 597 | * applies. If this is really a shmem page then the page lock
|
| 598 | * will prevent unexpected transitions.
|
| 599 |
|
| 600 | lock_page(page);
|
| 601 | shmem_swizzled = PageSwapCache(page) || page->mapping;
|
| 602 | unlock_page(page);
|
| 603 | put_page(page);
|
| 604 |
|
| 605 | if (shmem_swizzled)
|
| 606 | goto again;
|
| 607 |
|
| 608 | return -EFAULT;
|
| 609 | }
|
| 610 |
|
| 611 | |
| 612 | * Private mappings are handled in a simple way.
|
| 613 | *
|
| 614 | * If the futex key is stored on an anonymous page, then the associated
|
| 615 | * object is the mm which is implicitly pinned by the calling process.
|
| 616 | *
|
| 617 | * NOTE: When userspace waits on a MAP_SHARED mapping, even if
|
| 618 | * it's a read-only handle, it's expected that futexes attach to
|
| 619 | * the object not the particular process.
|
| 620 |
|
| 621 | if (PageAnon(page)) {
|
| 622 | |
| 623 | * A RO anonymous page will never change and thus doesn't make
|
| 624 | * sense for futex operations.
|
| 625 |
|
| 626 | if (unlikely(should_fail_futex(fshared)) || ro) {
|
| 627 | err = -EFAULT;
|
| 628 | goto out;
|
| 629 | }
|
| 630 |
|
| 631 | key->both.offset |= FUT_OFF_MMSHARED;
|
| 632 | key->private.mm = mm;
|
| 633 | key->private.address = address;
|
| 634 |
|
| 635 | } else {
|
| 636 | struct inode *inode;
|
| 637 |
|
| 638 | |
| 639 | * The associated futex object in this case is the inode and
|
| 640 | * the page->mapping must be traversed. Ordinarily this should
|
| 641 | * be stabilised under page lock but it's not strictly
|
| 642 | * necessary in this case as we just want to pin the inode, not
|
| 643 | * update the radix tree or anything like that.
|
| 644 | *
|
| 645 | * The RCU read lock is taken as the inode is finally freed
|
| 646 | * under RCU. If the mapping still matches expectations then the
|
| 647 | * mapping->host can be safely accessed as being a valid inode.
|
| 648 |
|
| 649 | rcu_read_lock();
|
| 650 |
|
| 651 | if (READ_ONCE(page->mapping) != mapping) {
|
| 652 | rcu_read_unlock();
|
| 653 | put_page(page);
|
| 654 |
|
| 655 | goto again;
|
| 656 | }
|
| 657 |
|
| 658 | inode = READ_ONCE(mapping->host);
|
| 659 | if (!inode) {
|
| 660 | rcu_read_unlock();
|
| 661 | put_page(page);
|
| 662 |
|
| 663 | goto again;
|
| 664 | }
|
| 665 |
|
| 666 | key->both.offset |= FUT_OFF_INODE;
|
| 667 | key->shared.i_seq = get_inode_sequence_number(inode);
|
| 668 | key->shared.pgoff = basepage_index(tail);
|
| 669 | rcu_read_unlock();
|
| 670 | }
|
| 671 |
|
| 672 | out:
|
| 673 | put_page(page);
|
| 674 | return err;
|
| 675 | }
|
| 676 |
|
| 677 | static inline void put_futex_key(union futex_key *key)
|
| 678 | {
|
| 679 | }
|
| 680 |
|
| 681 | |
| 682 | * fault_in_user_writeable() - Fault in user address and verify RW access
|
| 683 | * @uaddr: pointer to faulting user space address
|
| 684 | *
|
| 685 | * Slow path to fixup the fault we just took in the atomic write
|
| 686 | * access to @uaddr.
|
| 687 | *
|
| 688 | * We have no generic implementation of a non-destructive write to the
|
| 689 | * user address. We know that we faulted in the atomic pagefault
|
| 690 | * disabled section so we can as well avoid the #PF overhead by
|
| 691 | * calling get_user_pages() right away.
|
| 692 |
|
| 693 | static int fault_in_user_writeable(u32 __user *uaddr)
|
| 694 | {
|
| 695 | struct mm_struct *mm = current->mm;
|
| 696 | int ret;
|
| 697 |
|
| 698 | down_read(&mm->mmap_sem);
|
| 699 | ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
|
| 700 | FAULT_FLAG_WRITE, NULL);
|
| 701 | up_read(&mm->mmap_sem);
|
| 702 |
|
| 703 | return ret < 0 ? ret : 0;
|
| 704 | }
|
| 705 |
|
| 706 | |
| 707 | * futex_top_waiter() - Return the highest priority waiter on a futex
|
| 708 | * @hb: the hash bucket the futex_q's reside in
|
| 709 | * @key: the futex key (to distinguish it from other futex futex_q's)
|
| 710 | *
|
| 711 | * Must be called with the hb lock held.
|
| 712 |
|
| 713 | static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
|
| 714 | union futex_key *key)
|
| 715 | {
|
| 716 | struct futex_q *this;
|
| 717 |
|
| 718 | plist_for_each_entry(this, &hb->chain, list) {
|
| 719 | if (match_futex(&this->key, key))
|
| 720 | return this;
|
| 721 | }
|
| 722 | return NULL;
|
| 723 | }
|
| 724 |
|
| 725 | static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
|
| 726 | u32 uval, u32 newval)
|
| 727 | {
|
| 728 | int ret;
|
| 729 |
|
| 730 | pagefault_disable();
|
| 731 | ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
|
| 732 | pagefault_enable();
|
| 733 |
|
| 734 | return ret;
|
| 735 | }
|
| 736 |
|
| 737 | static int get_futex_value_locked(u32 *dest, u32 __user *from)
|
| 738 | {
|
| 739 | int ret;
|
| 740 |
|
| 741 | pagefault_disable();
|
| 742 | ret = __get_user(*dest, from);
|
| 743 | pagefault_enable();
|
| 744 |
|
| 745 | return ret ? -EFAULT : 0;
|
| 746 | }
|
| 747 |
|
| 748 |
|
| 749 | |
| 750 | * PI code:
|
| 751 |
|
| 752 | static int refill_pi_state_cache(void)
|
| 753 | {
|
| 754 | struct futex_pi_state *pi_state;
|
| 755 |
|
| 756 | if (likely(current->pi_state_cache))
|
| 757 | return 0;
|
| 758 |
|
| 759 | pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
|
| 760 |
|
| 761 | if (!pi_state)
|
| 762 | return -ENOMEM;
|
| 763 |
|
| 764 | INIT_LIST_HEAD(&pi_state->list);
|
| 765 |
|
| 766 | pi_state->owner = NULL;
|
| 767 | refcount_set(&pi_state->refcount, 1);
|
| 768 | pi_state->key = FUTEX_KEY_INIT;
|
| 769 |
|
| 770 | current->pi_state_cache = pi_state;
|
| 771 |
|
| 772 | return 0;
|
| 773 | }
|
| 774 |
|
| 775 | static struct futex_pi_state *alloc_pi_state(void)
|
| 776 | {
|
| 777 | struct futex_pi_state *pi_state = current->pi_state_cache;
|
| 778 |
|
| 779 | WARN_ON(!pi_state);
|
| 780 | current->pi_state_cache = NULL;
|
| 781 |
|
| 782 | return pi_state;
|
| 783 | }
|
| 784 |
|
| 785 | static void get_pi_state(struct futex_pi_state *pi_state)
|
| 786 | {
|
| 787 | WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
|
| 788 | }
|
| 789 |
|
| 790 | |
| 791 | * Drops a reference to the pi_state object and frees or caches it
|
| 792 | * when the last reference is gone.
|
| 793 |
|
| 794 | static void put_pi_state(struct futex_pi_state *pi_state)
|
| 795 | {
|
| 796 | if (!pi_state)
|
| 797 | return;
|
| 798 |
|
| 799 | if (!refcount_dec_and_test(&pi_state->refcount))
|
| 800 | return;
|
| 801 |
|
| 802 | |
| 803 | * If pi_state->owner is NULL, the owner is most probably dying
|
| 804 | * and has cleaned up the pi_state already
|
| 805 |
|
| 806 | if (pi_state->owner) {
|
| 807 | struct task_struct *owner;
|
| 808 |
|
| 809 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
|
| 810 | owner = pi_state->owner;
|
| 811 | if (owner) {
|
| 812 | raw_spin_lock(&owner->pi_lock);
|
| 813 | list_del_init(&pi_state->list);
|
| 814 | raw_spin_unlock(&owner->pi_lock);
|
| 815 | }
|
| 816 | rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner);
|
| 817 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
| 818 | }
|
| 819 |
|
| 820 | if (current->pi_state_cache) {
|
| 821 | kfree(pi_state);
|
| 822 | } else {
|
| 823 | |
| 824 | * pi_state->list is already empty.
|
| 825 | * clear pi_state->owner.
|
| 826 | * refcount is at 0 - put it back to 1.
|
| 827 |
|
| 828 | pi_state->owner = NULL;
|
| 829 | refcount_set(&pi_state->refcount, 1);
|
| 830 | current->pi_state_cache = pi_state;
|
| 831 | }
|
| 832 | }
|
| 833 |
|
| 834 | #ifdef CONFIG_FUTEX_PI
|
| 835 |
|
| 836 | |
| 837 | * This task is holding PI mutexes at exit time => bad.
|
| 838 | * Kernel cleans up PI-state, but userspace is likely hosed.
|
| 839 | * (Robust-futex cleanup is separate and might save the day for userspace.)
|
| 840 |
|
| 841 | static void exit_pi_state_list(struct task_struct *curr)
|
| 842 | {
|
| 843 | struct list_head *next, *head = &curr->pi_state_list;
|
| 844 | struct futex_pi_state *pi_state;
|
| 845 | struct futex_hash_bucket *hb;
|
| 846 | union futex_key key = FUTEX_KEY_INIT;
|
| 847 |
|
| 848 | if (!futex_cmpxchg_enabled)
|
| 849 | return;
|
| 850 | |
| 851 | * We are a ZOMBIE and nobody can enqueue itself on
|
| 852 | * pi_state_list anymore, but we have to be careful
|
| 853 | * versus waiters unqueueing themselves:
|
| 854 |
|
| 855 | raw_spin_lock_irq(&curr->pi_lock);
|
| 856 | while (!list_empty(head)) {
|
| 857 | next = head->next;
|
| 858 | pi_state = list_entry(next, struct futex_pi_state, list);
|
| 859 | key = pi_state->key;
|
| 860 | hb = hash_futex(&key);
|
| 861 |
|
| 862 | |
| 863 | * We can race against put_pi_state() removing itself from the
|
| 864 | * list (a waiter going away). put_pi_state() will first
|
| 865 | * decrement the reference count and then modify the list, so
|
| 866 | * its possible to see the list entry but fail this reference
|
| 867 | * acquire.
|
| 868 | *
|
| 869 | * In that case; drop the locks to let put_pi_state() make
|
| 870 | * progress and retry the loop.
|
| 871 |
|
| 872 | if (!refcount_inc_not_zero(&pi_state->refcount)) {
|
| 873 | raw_spin_unlock_irq(&curr->pi_lock);
|
| 874 | cpu_relax();
|
| 875 | raw_spin_lock_irq(&curr->pi_lock);
|
| 876 | continue;
|
| 877 | }
|
| 878 | raw_spin_unlock_irq(&curr->pi_lock);
|
| 879 |
|
| 880 | spin_lock(&hb->lock);
|
| 881 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
|
| 882 | raw_spin_lock(&curr->pi_lock);
|
| 883 | |
| 884 | * We dropped the pi-lock, so re-check whether this
|
| 885 | * task still owns the PI-state:
|
| 886 |
|
| 887 | if (head->next != next) {
|
| 888 |
|
| 889 | raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
|
| 890 | spin_unlock(&hb->lock);
|
| 891 | put_pi_state(pi_state);
|
| 892 | continue;
|
| 893 | }
|
| 894 |
|
| 895 | WARN_ON(pi_state->owner != curr);
|
| 896 | WARN_ON(list_empty(&pi_state->list));
|
| 897 | list_del_init(&pi_state->list);
|
| 898 | pi_state->owner = NULL;
|
| 899 |
|
| 900 | raw_spin_unlock(&curr->pi_lock);
|
| 901 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
| 902 | spin_unlock(&hb->lock);
|
| 903 |
|
| 904 | rt_mutex_futex_unlock(&pi_state->pi_mutex);
|
| 905 | put_pi_state(pi_state);
|
| 906 |
|
| 907 | raw_spin_lock_irq(&curr->pi_lock);
|
| 908 | }
|
| 909 | raw_spin_unlock_irq(&curr->pi_lock);
|
| 910 | }
|
| 911 | #else
|
| 912 | static inline void exit_pi_state_list(struct task_struct *curr) { }
|
| 913 | #endif
|
| 914 |
|
| 915 | |
| 916 | * We need to check the following states:
|
| 917 | *
|
| 918 | * Waiter | pi_state | pi->owner | uTID | uODIED | ?
|
| 919 | *
|
| 920 | * [1] NULL | --- | --- | 0 | 0/1 | Valid
|
| 921 | * [2] NULL | --- | --- | >0 | 0/1 | Valid
|
| 922 | *
|
| 923 | * [3] Found | NULL | -- | Any | 0/1 | Invalid
|
| 924 | *
|
| 925 | * [4] Found | Found | NULL | 0 | 1 | Valid
|
| 926 | * [5] Found | Found | NULL | >0 | 1 | Invalid
|
| 927 | *
|
| 928 | * [6] Found | Found | task | 0 | 1 | Valid
|
| 929 | *
|
| 930 | * [7] Found | Found | NULL | Any | 0 | Invalid
|
| 931 | *
|
| 932 | * [8] Found | Found | task | ==taskTID | 0/1 | Valid
|
| 933 | * [9] Found | Found | task | 0 | 0 | Invalid
|
| 934 | * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
|
| 935 | *
|
| 936 | * [1] Indicates that the kernel can acquire the futex atomically. We
|
| 937 | * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
|
| 938 | *
|
| 939 | * [2] Valid, if TID does not belong to a kernel thread. If no matching
|
| 940 | * thread is found then it indicates that the owner TID has died.
|
| 941 | *
|
| 942 | * [3] Invalid. The waiter is queued on a non PI futex
|
| 943 | *
|
| 944 | * [4] Valid state after exit_robust_list(), which sets the user space
|
| 945 | * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
|
| 946 | *
|
| 947 | * [5] The user space value got manipulated between exit_robust_list()
|
| 948 | * and exit_pi_state_list()
|
| 949 | *
|
| 950 | * [6] Valid state after exit_pi_state_list() which sets the new owner in
|
| 951 | * the pi_state but cannot access the user space value.
|
| 952 | *
|
| 953 | * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
|
| 954 | *
|
| 955 | * [8] Owner and user space value match
|
| 956 | *
|
| 957 | * [9] There is no transient state which sets the user space TID to 0
|
| 958 | * except exit_robust_list(), but this is indicated by the
|
| 959 | * FUTEX_OWNER_DIED bit. See [4]
|
| 960 | *
|
| 961 | * [10] There is no transient state which leaves owner and user space
|
| 962 | * TID out of sync.
|
| 963 | *
|
| 964 | *
|
| 965 | * Serialization and lifetime rules:
|
| 966 | *
|
| 967 | * hb->lock:
|
| 968 | *
|
| 969 | * hb -> futex_q, relation
|
| 970 | * futex_q -> pi_state, relation
|
| 971 | *
|
| 972 | * (cannot be raw because hb can contain arbitrary amount
|
| 973 | * of futex_q's)
|
| 974 | *
|
| 975 | * pi_mutex->wait_lock:
|
| 976 | *
|
| 977 | * {uval, pi_state}
|
| 978 | *
|
| 979 | * (and pi_mutex 'obviously')
|
| 980 | *
|
| 981 | * p->pi_lock:
|
| 982 | *
|
| 983 | * p->pi_state_list -> pi_state->list, relation
|
| 984 | *
|
| 985 | * pi_state->refcount:
|
| 986 | *
|
| 987 | * pi_state lifetime
|
| 988 | *
|
| 989 | *
|
| 990 | * Lock order:
|
| 991 | *
|
| 992 | * hb->lock
|
| 993 | * pi_mutex->wait_lock
|
| 994 | * p->pi_lock
|
| 995 | *
|
| 996 |
|
| 997 |
|
| 998 | |
| 999 | * Validate that the existing waiter has a pi_state and sanity check
|
| 1000 | * the pi_state against the user space value. If correct, attach to
|
| 1001 | * it.
|
| 1002 |
|
| 1003 | static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
|
| 1004 | struct futex_pi_state *pi_state,
|
| 1005 | struct futex_pi_state **ps)
|
| 1006 | {
|
| 1007 | pid_t pid = uval & FUTEX_TID_MASK;
|
| 1008 | u32 uval2;
|
| 1009 | int ret;
|
| 1010 |
|
| 1011 | |
| 1012 | * Userspace might have messed up non-PI and PI futexes [3]
|
| 1013 |
|
| 1014 | if (unlikely(!pi_state))
|
| 1015 | return -EINVAL;
|
| 1016 |
|
| 1017 | |
| 1018 | * We get here with hb->lock held, and having found a
|
| 1019 | * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
|
| 1020 | * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
|
| 1021 | * which in turn means that futex_lock_pi() still has a reference on
|
| 1022 | * our pi_state.
|
| 1023 | *
|
| 1024 | * The waiter holding a reference on @pi_state also protects against
|
| 1025 | * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
|
| 1026 | * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
|
| 1027 | * free pi_state before we can take a reference ourselves.
|
| 1028 |
|
| 1029 | WARN_ON(!refcount_read(&pi_state->refcount));
|
| 1030 |
|
| 1031 | |
| 1032 | * Now that we have a pi_state, we can acquire wait_lock
|
| 1033 | * and do the state validation.
|
| 1034 |
|
| 1035 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
|
| 1036 |
|
| 1037 | |
| 1038 | * Since {uval, pi_state} is serialized by wait_lock, and our current
|
| 1039 | * uval was read without holding it, it can have changed. Verify it
|
| 1040 | * still is what we expect it to be, otherwise retry the entire
|
| 1041 | * operation.
|
| 1042 |
|
| 1043 | if (get_futex_value_locked(&uval2, uaddr))
|
| 1044 | goto out_efault;
|
| 1045 |
|
| 1046 | if (uval != uval2)
|
| 1047 | goto out_eagain;
|
| 1048 |
|
| 1049 | |
| 1050 | * Handle the owner died case:
|
| 1051 |
|
| 1052 | if (uval & FUTEX_OWNER_DIED) {
|
| 1053 | |
| 1054 | * exit_pi_state_list sets owner to NULL and wakes the
|
| 1055 | * topmost waiter. The task which acquires the
|
| 1056 | * pi_state->rt_mutex will fixup owner.
|
| 1057 |
|
| 1058 | if (!pi_state->owner) {
|
| 1059 | |
| 1060 | * No pi state owner, but the user space TID
|
| 1061 | * is not 0. Inconsistent state. [5]
|
| 1062 |
|
| 1063 | if (pid)
|
| 1064 | goto out_einval;
|
| 1065 | |
| 1066 | * Take a ref on the state and return success. [4]
|
| 1067 |
|
| 1068 | goto out_attach;
|
| 1069 | }
|
| 1070 |
|
| 1071 | |
| 1072 | * If TID is 0, then either the dying owner has not
|
| 1073 | * yet executed exit_pi_state_list() or some waiter
|
| 1074 | * acquired the rtmutex in the pi state, but did not
|
| 1075 | * yet fixup the TID in user space.
|
| 1076 | *
|
| 1077 | * Take a ref on the state and return success. [6]
|
| 1078 |
|
| 1079 | if (!pid)
|
| 1080 | goto out_attach;
|
| 1081 | } else {
|
| 1082 | |
| 1083 | * If the owner died bit is not set, then the pi_state
|
| 1084 | * must have an owner. [7]
|
| 1085 |
|
| 1086 | if (!pi_state->owner)
|
| 1087 | goto out_einval;
|
| 1088 | }
|
| 1089 |
|
| 1090 | |
| 1091 | * Bail out if user space manipulated the futex value. If pi
|
| 1092 | * state exists then the owner TID must be the same as the
|
| 1093 | * user space TID. [9/10]
|
| 1094 |
|
| 1095 | if (pid != task_pid_vnr(pi_state->owner))
|
| 1096 | goto out_einval;
|
| 1097 |
|
| 1098 | out_attach:
|
| 1099 | get_pi_state(pi_state);
|
| 1100 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
| 1101 | *ps = pi_state;
|
| 1102 | return 0;
|
| 1103 |
|
| 1104 | out_einval:
|
| 1105 | ret = -EINVAL;
|
| 1106 | goto out_error;
|
| 1107 |
|
| 1108 | out_eagain:
|
| 1109 | ret = -EAGAIN;
|
| 1110 | goto out_error;
|
| 1111 |
|
| 1112 | out_efault:
|
| 1113 | ret = -EFAULT;
|
| 1114 | goto out_error;
|
| 1115 |
|
| 1116 | out_error:
|
| 1117 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
| 1118 | return ret;
|
| 1119 | }
|
| 1120 |
|
| 1121 | |
| 1122 | * wait_for_owner_exiting - Block until the owner has exited
|
| 1123 | * @ret: owner's current futex lock status
|
| 1124 | * @exiting: Pointer to the exiting task
|
| 1125 | *
|
| 1126 | * Caller must hold a refcount on @exiting.
|
| 1127 |
|
| 1128 | static void wait_for_owner_exiting(int ret, struct task_struct *exiting)
|
| 1129 | {
|
| 1130 | if (ret != -EBUSY) {
|
| 1131 | WARN_ON_ONCE(exiting);
|
| 1132 | return;
|
| 1133 | }
|
| 1134 |
|
| 1135 | if (WARN_ON_ONCE(ret == -EBUSY && !exiting))
|
| 1136 | return;
|
| 1137 |
|
| 1138 | mutex_lock(&exiting->futex_exit_mutex);
|
| 1139 | |
| 1140 | * No point in doing state checking here. If the waiter got here
|
| 1141 | * while the task was in exec()->exec_futex_release() then it can
|
| 1142 | * have any FUTEX_STATE_* value when the waiter has acquired the
|
| 1143 | * mutex. OK, if running, EXITING or DEAD if it reached exit()
|
| 1144 | * already. Highly unlikely and not a problem. Just one more round
|
| 1145 | * through the futex maze.
|
| 1146 |
|
| 1147 | mutex_unlock(&exiting->futex_exit_mutex);
|
| 1148 |
|
| 1149 | put_task_struct(exiting);
|
| 1150 | }
|
| 1151 |
|
| 1152 | static int handle_exit_race(u32 __user *uaddr, u32 uval,
|
| 1153 | struct task_struct *tsk)
|
| 1154 | {
|
| 1155 | u32 uval2;
|
| 1156 |
|
| 1157 | |
| 1158 | * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
|
| 1159 | * caller that the alleged owner is busy.
|
| 1160 |
|
| 1161 | if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
|
| 1162 | return -EBUSY;
|
| 1163 |
|
| 1164 | |
| 1165 | * Reread the user space value to handle the following situation:
|
| 1166 | *
|
| 1167 | * CPU0 CPU1
|
| 1168 | *
|
| 1169 | * sys_exit() sys_futex()
|
| 1170 | * do_exit() futex_lock_pi()
|
| 1171 | * futex_lock_pi_atomic()
|
| 1172 | * exit_signals(tsk) No waiters:
|
| 1173 | * tsk->flags |= PF_EXITING; *uaddr == 0x00000PID
|
| 1174 | * mm_release(tsk) Set waiter bit
|
| 1175 | * exit_robust_list(tsk) { *uaddr = 0x80000PID;
|
| 1176 | * Set owner died attach_to_pi_owner() {
|
| 1177 | * *uaddr = 0xC0000000; tsk = get_task(PID);
|
| 1178 | * } if (!tsk->flags & PF_EXITING) {
|
| 1179 | * ... attach();
|
| 1180 | * tsk->futex_state = } else {
|
| 1181 | * FUTEX_STATE_DEAD; if (tsk->futex_state !=
|
| 1182 | * FUTEX_STATE_DEAD)
|
| 1183 | * return -EAGAIN;
|
| 1184 | * return -ESRCH; <--- FAIL
|
| 1185 | * }
|
| 1186 | *
|
| 1187 | * Returning ESRCH unconditionally is wrong here because the
|
| 1188 | * user space value has been changed by the exiting task.
|
| 1189 | *
|
| 1190 | * The same logic applies to the case where the exiting task is
|
| 1191 | * already gone.
|
| 1192 |
|
| 1193 | if (get_futex_value_locked(&uval2, uaddr))
|
| 1194 | return -EFAULT;
|
| 1195 |
|
| 1196 |
|
| 1197 | if (uval2 != uval)
|
| 1198 | return -EAGAIN;
|
| 1199 |
|
| 1200 | |
| 1201 | * The exiting task did not have a robust list, the robust list was
|
| 1202 | * corrupted or the user space value in *uaddr is simply bogus.
|
| 1203 | * Give up and tell user space.
|
| 1204 |
|
| 1205 | return -ESRCH;
|
| 1206 | }
|
| 1207 |
|
| 1208 | |
| 1209 | * Lookup the task for the TID provided from user space and attach to
|
| 1210 | * it after doing proper sanity checks.
|
| 1211 |
|
| 1212 | static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key,
|
| 1213 | struct futex_pi_state **ps,
|
| 1214 | struct task_struct **exiting)
|
| 1215 | {
|
| 1216 | pid_t pid = uval & FUTEX_TID_MASK;
|
| 1217 | struct futex_pi_state *pi_state;
|
| 1218 | struct task_struct *p;
|
| 1219 |
|
| 1220 | |
| 1221 | * We are the first waiter - try to look up the real owner and attach
|
| 1222 | * the new pi_state to it, but bail out when TID = 0 [1]
|
| 1223 | *
|
| 1224 | * The !pid check is paranoid. None of the call sites should end up
|
| 1225 | * with pid == 0, but better safe than sorry. Let the caller retry
|
| 1226 |
|
| 1227 | if (!pid)
|
| 1228 | return -EAGAIN;
|
| 1229 | p = find_get_task_by_vpid(pid);
|
| 1230 | if (!p)
|
| 1231 | return handle_exit_race(uaddr, uval, NULL);
|
| 1232 |
|
| 1233 | if (unlikely(p->flags & PF_KTHREAD)) {
|
| 1234 | put_task_struct(p);
|
| 1235 | return -EPERM;
|
| 1236 | }
|
| 1237 |
|
| 1238 | |
| 1239 | * We need to look at the task state to figure out, whether the
|
| 1240 | * task is exiting. To protect against the change of the task state
|
| 1241 | * in futex_exit_release(), we do this protected by p->pi_lock:
|
| 1242 |
|
| 1243 | raw_spin_lock_irq(&p->pi_lock);
|
| 1244 | if (unlikely(p->futex_state != FUTEX_STATE_OK)) {
|
| 1245 | |
| 1246 | * The task is on the way out. When the futex state is
|
| 1247 | * FUTEX_STATE_DEAD, we know that the task has finished
|
| 1248 | * the cleanup:
|
| 1249 |
|
| 1250 | int ret = handle_exit_race(uaddr, uval, p);
|
| 1251 |
|
| 1252 | raw_spin_unlock_irq(&p->pi_lock);
|
| 1253 | |
| 1254 | * If the owner task is between FUTEX_STATE_EXITING and
|
| 1255 | * FUTEX_STATE_DEAD then store the task pointer and keep
|
| 1256 | * the reference on the task struct. The calling code will
|
| 1257 | * drop all locks, wait for the task to reach
|
| 1258 | * FUTEX_STATE_DEAD and then drop the refcount. This is
|
| 1259 | * required to prevent a live lock when the current task
|
| 1260 | * preempted the exiting task between the two states.
|
| 1261 |
|
| 1262 | if (ret == -EBUSY)
|
| 1263 | *exiting = p;
|
| 1264 | else
|
| 1265 | put_task_struct(p);
|
| 1266 | return ret;
|
| 1267 | }
|
| 1268 |
|
| 1269 | |
| 1270 | * No existing pi state. First waiter. [2]
|
| 1271 | *
|
| 1272 | * This creates pi_state, we have hb->lock held, this means nothing can
|
| 1273 | * observe this state, wait_lock is irrelevant.
|
| 1274 |
|
| 1275 | pi_state = alloc_pi_state();
|
| 1276 |
|
| 1277 | |
| 1278 | * Initialize the pi_mutex in locked state and make @p
|
| 1279 | * the owner of it:
|
| 1280 |
|
| 1281 | rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
|
| 1282 |
|
| 1283 |
|
| 1284 | pi_state->key = *key;
|
| 1285 |
|
| 1286 | WARN_ON(!list_empty(&pi_state->list));
|
| 1287 | list_add(&pi_state->list, &p->pi_state_list);
|
| 1288 | |
| 1289 | * Assignment without holding pi_state->pi_mutex.wait_lock is safe
|
| 1290 | * because there is no concurrency as the object is not published yet.
|
| 1291 |
|
| 1292 | pi_state->owner = p;
|
| 1293 | raw_spin_unlock_irq(&p->pi_lock);
|
| 1294 |
|
| 1295 | put_task_struct(p);
|
| 1296 |
|
| 1297 | *ps = pi_state;
|
| 1298 |
|
| 1299 | return 0;
|
| 1300 | }
|
| 1301 |
|
| 1302 | static int lookup_pi_state(u32 __user *uaddr, u32 uval,
|
| 1303 | struct futex_hash_bucket *hb,
|
| 1304 | union futex_key *key, struct futex_pi_state **ps,
|
| 1305 | struct task_struct **exiting)
|
| 1306 | {
|
| 1307 | struct futex_q *top_waiter = futex_top_waiter(hb, key);
|
| 1308 |
|
| 1309 | |
| 1310 | * If there is a waiter on that futex, validate it and
|
| 1311 | * attach to the pi_state when the validation succeeds.
|
| 1312 |
|
| 1313 | if (top_waiter)
|
| 1314 | return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
|
| 1315 |
|
| 1316 | |
| 1317 | * We are the first waiter - try to look up the owner based on
|
| 1318 | * @uval and attach to it.
|
| 1319 |
|
| 1320 | return attach_to_pi_owner(uaddr, uval, key, ps, exiting);
|
| 1321 | }
|
| 1322 |
|
| 1323 | static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
|
| 1324 | {
|
| 1325 | int err;
|
| 1326 | u32 uninitialized_var(curval);
|
| 1327 |
|
| 1328 | if (unlikely(should_fail_futex(true)))
|
| 1329 | return -EFAULT;
|
| 1330 |
|
| 1331 | err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
|
| 1332 | if (unlikely(err))
|
| 1333 | return err;
|
| 1334 |
|
| 1335 |
|
| 1336 | return curval != uval ? -EAGAIN : 0;
|
| 1337 | }
|
| 1338 |
|
| 1339 | |
| 1340 | * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
|
| 1341 | * @uaddr: the pi futex user address
|
| 1342 | * @hb: the pi futex hash bucket
|
| 1343 | * @key: the futex key associated with uaddr and hb
|
| 1344 | * @ps: the pi_state pointer where we store the result of the
|
| 1345 | * lookup
|
| 1346 | * @task: the task to perform the atomic lock work for. This will
|
| 1347 | * be "current" except in the case of requeue pi.
|
| 1348 | * @exiting: Pointer to store the task pointer of the owner task
|
| 1349 | * which is in the middle of exiting
|
| 1350 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
|
| 1351 | *
|
| 1352 | * Return:
|
| 1353 | * - 0 - ready to wait;
|
| 1354 | * - 1 - acquired the lock;
|
| 1355 | * - <0 - error
|
| 1356 | *
|
| 1357 | * The hb->lock and futex_key refs shall be held by the caller.
|
| 1358 | *
|
| 1359 | * @exiting is only set when the return value is -EBUSY. If so, this holds
|
| 1360 | * a refcount on the exiting task on return and the caller needs to drop it
|
| 1361 | * after waiting for the exit to complete.
|
| 1362 |
|
| 1363 | static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
|
| 1364 | union futex_key *key,
|
| 1365 | struct futex_pi_state **ps,
|
| 1366 | struct task_struct *task,
|
| 1367 | struct task_struct **exiting,
|
| 1368 | int set_waiters)
|
| 1369 | {
|
| 1370 | u32 uval, newval, vpid = task_pid_vnr(task);
|
| 1371 | struct futex_q *top_waiter;
|
| 1372 | int ret;
|
| 1373 |
|
| 1374 | |
| 1375 | * Read the user space value first so we can validate a few
|
| 1376 | * things before proceeding further.
|
| 1377 |
|
| 1378 | if (get_futex_value_locked(&uval, uaddr))
|
| 1379 | return -EFAULT;
|
| 1380 |
|
| 1381 | if (unlikely(should_fail_futex(true)))
|
| 1382 | return -EFAULT;
|
| 1383 |
|
| 1384 | |
| 1385 | * Detect deadlocks.
|
| 1386 |
|
| 1387 | if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
|
| 1388 | return -EDEADLK;
|
| 1389 |
|
| 1390 | if ((unlikely(should_fail_futex(true))))
|
| 1391 | return -EDEADLK;
|
| 1392 |
|
| 1393 | |
| 1394 | * Lookup existing state first. If it exists, try to attach to
|
| 1395 | * its pi_state.
|
| 1396 |
|
| 1397 | top_waiter = futex_top_waiter(hb, key);
|
| 1398 | if (top_waiter)
|
| 1399 | return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
|
| 1400 |
|
| 1401 | |
| 1402 | * No waiter and user TID is 0. We are here because the
|
| 1403 | * waiters or the owner died bit is set or called from
|
| 1404 | * requeue_cmp_pi or for whatever reason something took the
|
| 1405 | * syscall.
|
| 1406 |
|
| 1407 | if (!(uval & FUTEX_TID_MASK)) {
|
| 1408 | |
| 1409 | * We take over the futex. No other waiters and the user space
|
| 1410 | * TID is 0. We preserve the owner died bit.
|
| 1411 |
|
| 1412 | newval = uval & FUTEX_OWNER_DIED;
|
| 1413 | newval |= vpid;
|
| 1414 |
|
| 1415 |
|
| 1416 | if (set_waiters)
|
| 1417 | newval |= FUTEX_WAITERS;
|
| 1418 |
|
| 1419 | ret = lock_pi_update_atomic(uaddr, uval, newval);
|
| 1420 |
|
| 1421 | return ret < 0 ? ret : 1;
|
| 1422 | }
|
| 1423 |
|
| 1424 | |
| 1425 | * First waiter. Set the waiters bit before attaching ourself to
|
| 1426 | * the owner. If owner tries to unlock, it will be forced into
|
| 1427 | * the kernel and blocked on hb->lock.
|
| 1428 |
|
| 1429 | newval = uval | FUTEX_WAITERS;
|
| 1430 | ret = lock_pi_update_atomic(uaddr, uval, newval);
|
| 1431 | if (ret)
|
| 1432 | return ret;
|
| 1433 | |
| 1434 | * If the update of the user space value succeeded, we try to
|
| 1435 | * attach to the owner. If that fails, no harm done, we only
|
| 1436 | * set the FUTEX_WAITERS bit in the user space variable.
|
| 1437 |
|
| 1438 | return attach_to_pi_owner(uaddr, newval, key, ps, exiting);
|
| 1439 | }
|
| 1440 |
|
| 1441 | |
| 1442 | * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
|
| 1443 | * @q: The futex_q to unqueue
|
| 1444 | *
|
| 1445 | * The q->lock_ptr must not be NULL and must be held by the caller.
|
| 1446 |
|
| 1447 | static void __unqueue_futex(struct futex_q *q)
|
| 1448 | {
|
| 1449 | struct futex_hash_bucket *hb;
|
| 1450 |
|
| 1451 | if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list)))
|
| 1452 | return;
|
| 1453 | lockdep_assert_held(q->lock_ptr);
|
| 1454 |
|
| 1455 | hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
|
| 1456 | plist_del(&q->list, &hb->chain);
|
| 1457 | hb_waiters_dec(hb);
|
| 1458 | }
|
| 1459 |
|
| 1460 | |
| 1461 | * The hash bucket lock must be held when this is called.
|
| 1462 | * Afterwards, the futex_q must not be accessed. Callers
|
| 1463 | * must ensure to later call wake_up_q() for the actual
|
| 1464 | * wakeups to occur.
|
| 1465 |
|
| 1466 | static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
|
| 1467 | {
|
| 1468 | struct task_struct *p = q->task;
|
| 1469 |
|
| 1470 | if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
|
| 1471 | return;
|
| 1472 |
|
| 1473 | get_task_struct(p);
|
| 1474 | __unqueue_futex(q);
|
| 1475 | |
| 1476 | * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
|
| 1477 | * is written, without taking any locks. This is possible in the event
|
| 1478 | * of a spurious wakeup, for example. A memory barrier is required here
|
| 1479 | * to prevent the following store to lock_ptr from getting ahead of the
|
| 1480 | * plist_del in __unqueue_futex().
|
| 1481 |
|
| 1482 | smp_store_release(&q->lock_ptr, NULL);
|
| 1483 |
|
| 1484 | |
| 1485 | * Queue the task for later wakeup for after we've released
|
| 1486 | * the hb->lock.
|
| 1487 |
|
| 1488 | wake_q_add_safe(wake_q, p);
|
| 1489 | }
|
| 1490 |
|
| 1491 | |
| 1492 | * Caller must hold a reference on @pi_state.
|
| 1493 |
|
| 1494 | static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
|
| 1495 | {
|
| 1496 | u32 uninitialized_var(curval), newval;
|
| 1497 | struct task_struct *new_owner;
|
| 1498 | bool postunlock = false;
|
| 1499 | DEFINE_WAKE_Q(wake_q);
|
| 1500 | int ret = 0;
|
| 1501 |
|
| 1502 | new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
|
| 1503 | if (WARN_ON_ONCE(!new_owner)) {
|
| 1504 | |
| 1505 | * As per the comment in futex_unlock_pi() this should not happen.
|
| 1506 | *
|
| 1507 | * When this happens, give up our locks and try again, giving
|
| 1508 | * the futex_lock_pi() instance time to complete, either by
|
| 1509 | * waiting on the rtmutex or removing itself from the futex
|
| 1510 | * queue.
|
| 1511 |
|
| 1512 | ret = -EAGAIN;
|
| 1513 | goto out_unlock;
|
| 1514 | }
|
| 1515 |
|
| 1516 | |
| 1517 | * We pass it to the next owner. The WAITERS bit is always kept
|
| 1518 | * enabled while there is PI state around. We cleanup the owner
|
| 1519 | * died bit, because we are the owner.
|
| 1520 |
|
| 1521 | newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
|
| 1522 |
|
| 1523 | if (unlikely(should_fail_futex(true)))
|
| 1524 | ret = -EFAULT;
|
| 1525 |
|
| 1526 | ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
|
| 1527 | if (!ret && (curval != uval)) {
|
| 1528 | |
| 1529 | * If a unconditional UNLOCK_PI operation (user space did not
|
| 1530 | * try the TID->0 transition) raced with a waiter setting the
|
| 1531 | * FUTEX_WAITERS flag between get_user() and locking the hash
|
| 1532 | * bucket lock, retry the operation.
|
| 1533 |
|
| 1534 | if ((FUTEX_TID_MASK & curval) == uval)
|
| 1535 | ret = -EAGAIN;
|
| 1536 | else
|
| 1537 | ret = -EINVAL;
|
| 1538 | }
|
| 1539 |
|
| 1540 | if (ret)
|
| 1541 | goto out_unlock;
|
| 1542 |
|
| 1543 | |
| 1544 | * This is a point of no return; once we modify the uval there is no
|
| 1545 | * going back and subsequent operations must not fail.
|
| 1546 |
|
| 1547 |
|
| 1548 | raw_spin_lock(&pi_state->owner->pi_lock);
|
| 1549 | WARN_ON(list_empty(&pi_state->list));
|
| 1550 | list_del_init(&pi_state->list);
|
| 1551 | raw_spin_unlock(&pi_state->owner->pi_lock);
|
| 1552 |
|
| 1553 | raw_spin_lock(&new_owner->pi_lock);
|
| 1554 | WARN_ON(!list_empty(&pi_state->list));
|
| 1555 | list_add(&pi_state->list, &new_owner->pi_state_list);
|
| 1556 | pi_state->owner = new_owner;
|
| 1557 | raw_spin_unlock(&new_owner->pi_lock);
|
| 1558 |
|
| 1559 | postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
|
| 1560 |
|
| 1561 | out_unlock:
|
| 1562 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
| 1563 |
|
| 1564 | if (postunlock)
|
| 1565 | rt_mutex_postunlock(&wake_q);
|
| 1566 |
|
| 1567 | return ret;
|
| 1568 | }
|
| 1569 |
|
| 1570 | |
| 1571 | * Express the locking dependencies for lockdep:
|
| 1572 |
|
| 1573 | static inline void
|
| 1574 | double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
|
| 1575 | {
|
| 1576 | if (hb1 <= hb2) {
|
| 1577 | spin_lock(&hb1->lock);
|
| 1578 | if (hb1 < hb2)
|
| 1579 | spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
|
| 1580 | } else {
|
| 1581 | spin_lock(&hb2->lock);
|
| 1582 | spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
|
| 1583 | }
|
| 1584 | }
|
| 1585 |
|
| 1586 | static inline void
|
| 1587 | double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
|
| 1588 | {
|
| 1589 | spin_unlock(&hb1->lock);
|
| 1590 | if (hb1 != hb2)
|
| 1591 | spin_unlock(&hb2->lock);
|
| 1592 | }
|
| 1593 |
|
| 1594 | |
| 1595 | * Wake up waiters matching bitset queued on this futex (uaddr).
|
| 1596 |
|
| 1597 | static int
|
| 1598 | futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
|
| 1599 | {
|
| 1600 | struct futex_hash_bucket *hb;
|
| 1601 | struct futex_q *this, *next;
|
| 1602 | union futex_key key = FUTEX_KEY_INIT;
|
| 1603 | int ret;
|
| 1604 | DEFINE_WAKE_Q(wake_q);
|
| 1605 |
|
| 1606 | if (!bitset)
|
| 1607 | return -EINVAL;
|
| 1608 |
|
| 1609 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ);
|
| 1610 | if (unlikely(ret != 0))
|
| 1611 | goto out;
|
| 1612 |
|
| 1613 | hb = hash_futex(&key);
|
| 1614 |
|
| 1615 |
|
| 1616 | if (!hb_waiters_pending(hb))
|
| 1617 | goto out_put_key;
|
| 1618 |
|
| 1619 | spin_lock(&hb->lock);
|
| 1620 |
|
| 1621 | plist_for_each_entry_safe(this, next, &hb->chain, list) {
|
| 1622 | if (match_futex (&this->key, &key)) {
|
| 1623 | if (this->pi_state || this->rt_waiter) {
|
| 1624 | ret = -EINVAL;
|
| 1625 | break;
|
| 1626 | }
|
| 1627 |
|
| 1628 |
|
| 1629 | if (!(this->bitset & bitset))
|
| 1630 | continue;
|
| 1631 |
|
| 1632 | mark_wake_futex(&wake_q, this);
|
| 1633 | if (++ret >= nr_wake)
|
| 1634 | break;
|
| 1635 | }
|
| 1636 | }
|
| 1637 |
|
| 1638 | spin_unlock(&hb->lock);
|
| 1639 | wake_up_q(&wake_q);
|
| 1640 | out_put_key:
|
| 1641 | put_futex_key(&key);
|
| 1642 | out:
|
| 1643 | return ret;
|
| 1644 | }
|
| 1645 |
|
| 1646 | static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
|
| 1647 | {
|
| 1648 | unsigned int op = (encoded_op & 0x70000000) >> 28;
|
| 1649 | unsigned int cmp = (encoded_op & 0x0f000000) >> 24;
|
| 1650 | int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11);
|
| 1651 | int cmparg = sign_extend32(encoded_op & 0x00000fff, 11);
|
| 1652 | int oldval, ret;
|
| 1653 |
|
| 1654 | if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
|
| 1655 | if (oparg < 0 || oparg > 31) {
|
| 1656 | char comm[sizeof(current->comm)];
|
| 1657 | |
| 1658 | * kill this print and return -EINVAL when userspace
|
| 1659 | * is sane again
|
| 1660 |
|
| 1661 | pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n",
|
| 1662 | get_task_comm(comm, current), oparg);
|
| 1663 | oparg &= 31;
|
| 1664 | }
|
| 1665 | oparg = 1 << oparg;
|
| 1666 | }
|
| 1667 |
|
| 1668 | pagefault_disable();
|
| 1669 | ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
|
| 1670 | pagefault_enable();
|
| 1671 | if (ret)
|
| 1672 | return ret;
|
| 1673 |
|
| 1674 | switch (cmp) {
|
| 1675 | case FUTEX_OP_CMP_EQ:
|
| 1676 | return oldval == cmparg;
|
| 1677 | case FUTEX_OP_CMP_NE:
|
| 1678 | return oldval != cmparg;
|
| 1679 | case FUTEX_OP_CMP_LT:
|
| 1680 | return oldval < cmparg;
|
| 1681 | case FUTEX_OP_CMP_GE:
|
| 1682 | return oldval >= cmparg;
|
| 1683 | case FUTEX_OP_CMP_LE:
|
| 1684 | return oldval <= cmparg;
|
| 1685 | case FUTEX_OP_CMP_GT:
|
| 1686 | return oldval > cmparg;
|
| 1687 | default:
|
| 1688 | return -ENOSYS;
|
| 1689 | }
|
| 1690 | }
|
| 1691 |
|
| 1692 | |
| 1693 | * Wake up all waiters hashed on the physical page that is mapped
|
| 1694 | * to this virtual address:
|
| 1695 |
|
| 1696 | static int
|
| 1697 | futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
|
| 1698 | int nr_wake, int nr_wake2, int op)
|
| 1699 | {
|
| 1700 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
|
| 1701 | struct futex_hash_bucket *hb1, *hb2;
|
| 1702 | struct futex_q *this, *next;
|
| 1703 | int ret, op_ret;
|
| 1704 | DEFINE_WAKE_Q(wake_q);
|
| 1705 |
|
| 1706 | retry:
|
| 1707 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
|
| 1708 | if (unlikely(ret != 0))
|
| 1709 | goto out;
|
| 1710 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
|
| 1711 | if (unlikely(ret != 0))
|
| 1712 | goto out_put_key1;
|
| 1713 |
|
| 1714 | hb1 = hash_futex(&key1);
|
| 1715 | hb2 = hash_futex(&key2);
|
| 1716 |
|
| 1717 | retry_private:
|
| 1718 | double_lock_hb(hb1, hb2);
|
| 1719 | op_ret = futex_atomic_op_inuser(op, uaddr2);
|
| 1720 | if (unlikely(op_ret < 0)) {
|
| 1721 | double_unlock_hb(hb1, hb2);
|
| 1722 |
|
| 1723 | if (!IS_ENABLED(CONFIG_MMU) ||
|
| 1724 | unlikely(op_ret != -EFAULT && op_ret != -EAGAIN)) {
|
| 1725 | |
| 1726 | * we don't get EFAULT from MMU faults if we don't have
|
| 1727 | * an MMU, but we might get them from range checking
|
| 1728 |
|
| 1729 | ret = op_ret;
|
| 1730 | goto out_put_keys;
|
| 1731 | }
|
| 1732 |
|
| 1733 | if (op_ret == -EFAULT) {
|
| 1734 | ret = fault_in_user_writeable(uaddr2);
|
| 1735 | if (ret)
|
| 1736 | goto out_put_keys;
|
| 1737 | }
|
| 1738 |
|
| 1739 | if (!(flags & FLAGS_SHARED)) {
|
| 1740 | cond_resched();
|
| 1741 | goto retry_private;
|
| 1742 | }
|
| 1743 |
|
| 1744 | put_futex_key(&key2);
|
| 1745 | put_futex_key(&key1);
|
| 1746 | cond_resched();
|
| 1747 | goto retry;
|
| 1748 | }
|
| 1749 |
|
| 1750 | plist_for_each_entry_safe(this, next, &hb1->chain, list) {
|
| 1751 | if (match_futex (&this->key, &key1)) {
|
| 1752 | if (this->pi_state || this->rt_waiter) {
|
| 1753 | ret = -EINVAL;
|
| 1754 | goto out_unlock;
|
| 1755 | }
|
| 1756 | mark_wake_futex(&wake_q, this);
|
| 1757 | if (++ret >= nr_wake)
|
| 1758 | break;
|
| 1759 | }
|
| 1760 | }
|
| 1761 |
|
| 1762 | if (op_ret > 0) {
|
| 1763 | op_ret = 0;
|
| 1764 | plist_for_each_entry_safe(this, next, &hb2->chain, list) {
|
| 1765 | if (match_futex (&this->key, &key2)) {
|
| 1766 | if (this->pi_state || this->rt_waiter) {
|
| 1767 | ret = -EINVAL;
|
| 1768 | goto out_unlock;
|
| 1769 | }
|
| 1770 | mark_wake_futex(&wake_q, this);
|
| 1771 | if (++op_ret >= nr_wake2)
|
| 1772 | break;
|
| 1773 | }
|
| 1774 | }
|
| 1775 | ret += op_ret;
|
| 1776 | }
|
| 1777 |
|
| 1778 | out_unlock:
|
| 1779 | double_unlock_hb(hb1, hb2);
|
| 1780 | wake_up_q(&wake_q);
|
| 1781 | out_put_keys:
|
| 1782 | put_futex_key(&key2);
|
| 1783 | out_put_key1:
|
| 1784 | put_futex_key(&key1);
|
| 1785 | out:
|
| 1786 | return ret;
|
| 1787 | }
|
| 1788 |
|
| 1789 | |
| 1790 | * requeue_futex() - Requeue a futex_q from one hb to another
|
| 1791 | * @q: the futex_q to requeue
|
| 1792 | * @hb1: the source hash_bucket
|
| 1793 | * @hb2: the target hash_bucket
|
| 1794 | * @key2: the new key for the requeued futex_q
|
| 1795 |
|
| 1796 | static inline
|
| 1797 | void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
|
| 1798 | struct futex_hash_bucket *hb2, union futex_key *key2)
|
| 1799 | {
|
| 1800 |
|
| 1801 | |
| 1802 | * If key1 and key2 hash to the same bucket, no need to
|
| 1803 | * requeue.
|
| 1804 |
|
| 1805 | if (likely(&hb1->chain != &hb2->chain)) {
|
| 1806 | plist_del(&q->list, &hb1->chain);
|
| 1807 | hb_waiters_dec(hb1);
|
| 1808 | hb_waiters_inc(hb2);
|
| 1809 | plist_add(&q->list, &hb2->chain);
|
| 1810 | q->lock_ptr = &hb2->lock;
|
| 1811 | }
|
| 1812 | q->key = *key2;
|
| 1813 | }
|
| 1814 |
|
| 1815 | |
| 1816 | * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
|
| 1817 | * @q: the futex_q
|
| 1818 | * @key: the key of the requeue target futex
|
| 1819 | * @hb: the hash_bucket of the requeue target futex
|
| 1820 | *
|
| 1821 | * During futex_requeue, with requeue_pi=1, it is possible to acquire the
|
| 1822 | * target futex if it is uncontended or via a lock steal. Set the futex_q key
|
| 1823 | * to the requeue target futex so the waiter can detect the wakeup on the right
|
| 1824 | * futex, but remove it from the hb and NULL the rt_waiter so it can detect
|
| 1825 | * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
|
| 1826 | * to protect access to the pi_state to fixup the owner later. Must be called
|
| 1827 | * with both q->lock_ptr and hb->lock held.
|
| 1828 |
|
| 1829 | static inline
|
| 1830 | void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
|
| 1831 | struct futex_hash_bucket *hb)
|
| 1832 | {
|
| 1833 | q->key = *key;
|
| 1834 |
|
| 1835 | __unqueue_futex(q);
|
| 1836 |
|
| 1837 | WARN_ON(!q->rt_waiter);
|
| 1838 | q->rt_waiter = NULL;
|
| 1839 |
|
| 1840 | q->lock_ptr = &hb->lock;
|
| 1841 |
|
| 1842 | wake_up_state(q->task, TASK_NORMAL);
|
| 1843 | }
|
| 1844 |
|
| 1845 | |
| 1846 | * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
|
| 1847 | * @pifutex: the user address of the to futex
|
| 1848 | * @hb1: the from futex hash bucket, must be locked by the caller
|
| 1849 | * @hb2: the to futex hash bucket, must be locked by the caller
|
| 1850 | * @key1: the from futex key
|
| 1851 | * @key2: the to futex key
|
| 1852 | * @ps: address to store the pi_state pointer
|
| 1853 | * @exiting: Pointer to store the task pointer of the owner task
|
| 1854 | * which is in the middle of exiting
|
| 1855 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
|
| 1856 | *
|
| 1857 | * Try and get the lock on behalf of the top waiter if we can do it atomically.
|
| 1858 | * Wake the top waiter if we succeed. If the caller specified set_waiters,
|
| 1859 | * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
|
| 1860 | * hb1 and hb2 must be held by the caller.
|
| 1861 | *
|
| 1862 | * @exiting is only set when the return value is -EBUSY. If so, this holds
|
| 1863 | * a refcount on the exiting task on return and the caller needs to drop it
|
| 1864 | * after waiting for the exit to complete.
|
| 1865 | *
|
| 1866 | * Return:
|
| 1867 | * - 0 - failed to acquire the lock atomically;
|
| 1868 | * - >0 - acquired the lock, return value is vpid of the top_waiter
|
| 1869 | * - <0 - error
|
| 1870 |
|
| 1871 | static int
|
| 1872 | futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1,
|
| 1873 | struct futex_hash_bucket *hb2, union futex_key *key1,
|
| 1874 | union futex_key *key2, struct futex_pi_state **ps,
|
| 1875 | struct task_struct **exiting, int set_waiters)
|
| 1876 | {
|
| 1877 | struct futex_q *top_waiter = NULL;
|
| 1878 | u32 curval;
|
| 1879 | int ret, vpid;
|
| 1880 |
|
| 1881 | if (get_futex_value_locked(&curval, pifutex))
|
| 1882 | return -EFAULT;
|
| 1883 |
|
| 1884 | if (unlikely(should_fail_futex(true)))
|
| 1885 | return -EFAULT;
|
| 1886 |
|
| 1887 | |
| 1888 | * Find the top_waiter and determine if there are additional waiters.
|
| 1889 | * If the caller intends to requeue more than 1 waiter to pifutex,
|
| 1890 | * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
|
| 1891 | * as we have means to handle the possible fault. If not, don't set
|
| 1892 | * the bit unecessarily as it will force the subsequent unlock to enter
|
| 1893 | * the kernel.
|
| 1894 |
|
| 1895 | top_waiter = futex_top_waiter(hb1, key1);
|
| 1896 |
|
| 1897 |
|
| 1898 | if (!top_waiter)
|
| 1899 | return 0;
|
| 1900 |
|
| 1901 |
|
| 1902 | if (!match_futex(top_waiter->requeue_pi_key, key2))
|
| 1903 | return -EINVAL;
|
| 1904 |
|
| 1905 | |
| 1906 | * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
|
| 1907 | * the contended case or if set_waiters is 1. The pi_state is returned
|
| 1908 | * in ps in contended cases.
|
| 1909 |
|
| 1910 | vpid = task_pid_vnr(top_waiter->task);
|
| 1911 | ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
|
| 1912 | exiting, set_waiters);
|
| 1913 | if (ret == 1) {
|
| 1914 | requeue_pi_wake_futex(top_waiter, key2, hb2);
|
| 1915 | return vpid;
|
| 1916 | }
|
| 1917 | return ret;
|
| 1918 | }
|
| 1919 |
|
| 1920 | |
| 1921 | * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
|
| 1922 | * @uaddr1: source futex user address
|
| 1923 | * @flags: futex flags (FLAGS_SHARED, etc.)
|
| 1924 | * @uaddr2: target futex user address
|
| 1925 | * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
|
| 1926 | * @nr_requeue: number of waiters to requeue (0-INT_MAX)
|
| 1927 | * @cmpval: @uaddr1 expected value (or %NULL)
|
| 1928 | * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
|
| 1929 | * pi futex (pi to pi requeue is not supported)
|
| 1930 | *
|
| 1931 | * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
|
| 1932 | * uaddr2 atomically on behalf of the top waiter.
|
| 1933 | *
|
| 1934 | * Return:
|
| 1935 | * - >=0 - on success, the number of tasks requeued or woken;
|
| 1936 | * - <0 - on error
|
| 1937 |
|
| 1938 | static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
|
| 1939 | u32 __user *uaddr2, int nr_wake, int nr_requeue,
|
| 1940 | u32 *cmpval, int requeue_pi)
|
| 1941 | {
|
| 1942 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
|
| 1943 | int task_count = 0, ret;
|
| 1944 | struct futex_pi_state *pi_state = NULL;
|
| 1945 | struct futex_hash_bucket *hb1, *hb2;
|
| 1946 | struct futex_q *this, *next;
|
| 1947 | DEFINE_WAKE_Q(wake_q);
|
| 1948 |
|
| 1949 | if (nr_wake < 0 || nr_requeue < 0)
|
| 1950 | return -EINVAL;
|
| 1951 |
|
| 1952 | |
| 1953 | * When PI not supported: return -ENOSYS if requeue_pi is true,
|
| 1954 | * consequently the compiler knows requeue_pi is always false past
|
| 1955 | * this point which will optimize away all the conditional code
|
| 1956 | * further down.
|
| 1957 |
|
| 1958 | if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi)
|
| 1959 | return -ENOSYS;
|
| 1960 |
|
| 1961 | if (requeue_pi) {
|
| 1962 | |
| 1963 | * Requeue PI only works on two distinct uaddrs. This
|
| 1964 | * check is only valid for private futexes. See below.
|
| 1965 |
|
| 1966 | if (uaddr1 == uaddr2)
|
| 1967 | return -EINVAL;
|
| 1968 |
|
| 1969 | |
| 1970 | * requeue_pi requires a pi_state, try to allocate it now
|
| 1971 | * without any locks in case it fails.
|
| 1972 |
|
| 1973 | if (refill_pi_state_cache())
|
| 1974 | return -ENOMEM;
|
| 1975 | |
| 1976 | * requeue_pi must wake as many tasks as it can, up to nr_wake
|
| 1977 | * + nr_requeue, since it acquires the rt_mutex prior to
|
| 1978 | * returning to userspace, so as to not leave the rt_mutex with
|
| 1979 | * waiters and no owner. However, second and third wake-ups
|
| 1980 | * cannot be predicted as they involve race conditions with the
|
| 1981 | * first wake and a fault while looking up the pi_state. Both
|
| 1982 | * pthread_cond_signal() and pthread_cond_broadcast() should
|
| 1983 | * use nr_wake=1.
|
| 1984 |
|
| 1985 | if (nr_wake != 1)
|
| 1986 | return -EINVAL;
|
| 1987 | }
|
| 1988 |
|
| 1989 | retry:
|
| 1990 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
|
| 1991 | if (unlikely(ret != 0))
|
| 1992 | goto out;
|
| 1993 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
|
| 1994 | requeue_pi ? FUTEX_WRITE : FUTEX_READ);
|
| 1995 | if (unlikely(ret != 0))
|
| 1996 | goto out_put_key1;
|
| 1997 |
|
| 1998 | |
| 1999 | * The check above which compares uaddrs is not sufficient for
|
| 2000 | * shared futexes. We need to compare the keys:
|
| 2001 |
|
| 2002 | if (requeue_pi && match_futex(&key1, &key2)) {
|
| 2003 | ret = -EINVAL;
|
| 2004 | goto out_put_keys;
|
| 2005 | }
|
| 2006 |
|
| 2007 | hb1 = hash_futex(&key1);
|
| 2008 | hb2 = hash_futex(&key2);
|
| 2009 |
|
| 2010 | retry_private:
|
| 2011 | hb_waiters_inc(hb2);
|
| 2012 | double_lock_hb(hb1, hb2);
|
| 2013 |
|
| 2014 | if (likely(cmpval != NULL)) {
|
| 2015 | u32 curval;
|
| 2016 |
|
| 2017 | ret = get_futex_value_locked(&curval, uaddr1);
|
| 2018 |
|
| 2019 | if (unlikely(ret)) {
|
| 2020 | double_unlock_hb(hb1, hb2);
|
| 2021 | hb_waiters_dec(hb2);
|
| 2022 |
|
| 2023 | ret = get_user(curval, uaddr1);
|
| 2024 | if (ret)
|
| 2025 | goto out_put_keys;
|
| 2026 |
|
| 2027 | if (!(flags & FLAGS_SHARED))
|
| 2028 | goto retry_private;
|
| 2029 |
|
| 2030 | put_futex_key(&key2);
|
| 2031 | put_futex_key(&key1);
|
| 2032 | goto retry;
|
| 2033 | }
|
| 2034 | if (curval != *cmpval) {
|
| 2035 | ret = -EAGAIN;
|
| 2036 | goto out_unlock;
|
| 2037 | }
|
| 2038 | }
|
| 2039 |
|
| 2040 | if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
|
| 2041 | struct task_struct *exiting = NULL;
|
| 2042 |
|
| 2043 | |
| 2044 | * Attempt to acquire uaddr2 and wake the top waiter. If we
|
| 2045 | * intend to requeue waiters, force setting the FUTEX_WAITERS
|
| 2046 | * bit. We force this here where we are able to easily handle
|
| 2047 | * faults rather in the requeue loop below.
|
| 2048 |
|
| 2049 | ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
|
| 2050 | &key2, &pi_state,
|
| 2051 | &exiting, nr_requeue);
|
| 2052 |
|
| 2053 | |
| 2054 | * At this point the top_waiter has either taken uaddr2 or is
|
| 2055 | * waiting on it. If the former, then the pi_state will not
|
| 2056 | * exist yet, look it up one more time to ensure we have a
|
| 2057 | * reference to it. If the lock was taken, ret contains the
|
| 2058 | * vpid of the top waiter task.
|
| 2059 | * If the lock was not taken, we have pi_state and an initial
|
| 2060 | * refcount on it. In case of an error we have nothing.
|
| 2061 |
|
| 2062 | if (ret > 0) {
|
| 2063 | WARN_ON(pi_state);
|
| 2064 | task_count++;
|
| 2065 | |
| 2066 | * If we acquired the lock, then the user space value
|
| 2067 | * of uaddr2 should be vpid. It cannot be changed by
|
| 2068 | * the top waiter as it is blocked on hb2 lock if it
|
| 2069 | * tries to do so. If something fiddled with it behind
|
| 2070 | * our back the pi state lookup might unearth it. So
|
| 2071 | * we rather use the known value than rereading and
|
| 2072 | * handing potential crap to lookup_pi_state.
|
| 2073 | *
|
| 2074 | * If that call succeeds then we have pi_state and an
|
| 2075 | * initial refcount on it.
|
| 2076 |
|
| 2077 | ret = lookup_pi_state(uaddr2, ret, hb2, &key2,
|
| 2078 | &pi_state, &exiting);
|
| 2079 | }
|
| 2080 |
|
| 2081 | switch (ret) {
|
| 2082 | case 0:
|
| 2083 |
|
| 2084 | break;
|
| 2085 |
|
| 2086 |
|
| 2087 | case -EFAULT:
|
| 2088 | double_unlock_hb(hb1, hb2);
|
| 2089 | hb_waiters_dec(hb2);
|
| 2090 | put_futex_key(&key2);
|
| 2091 | put_futex_key(&key1);
|
| 2092 | ret = fault_in_user_writeable(uaddr2);
|
| 2093 | if (!ret)
|
| 2094 | goto retry;
|
| 2095 | goto out;
|
| 2096 | case -EBUSY:
|
| 2097 | case -EAGAIN:
|
| 2098 | |
| 2099 | * Two reasons for this:
|
| 2100 | * - EBUSY: Owner is exiting and we just wait for the
|
| 2101 | * exit to complete.
|
| 2102 | * - EAGAIN: The user space value changed.
|
| 2103 |
|
| 2104 | double_unlock_hb(hb1, hb2);
|
| 2105 | hb_waiters_dec(hb2);
|
| 2106 | put_futex_key(&key2);
|
| 2107 | put_futex_key(&key1);
|
| 2108 | |
| 2109 | * Handle the case where the owner is in the middle of
|
| 2110 | * exiting. Wait for the exit to complete otherwise
|
| 2111 | * this task might loop forever, aka. live lock.
|
| 2112 |
|
| 2113 | wait_for_owner_exiting(ret, exiting);
|
| 2114 | cond_resched();
|
| 2115 | goto retry;
|
| 2116 | default:
|
| 2117 | goto out_unlock;
|
| 2118 | }
|
| 2119 | }
|
| 2120 |
|
| 2121 | plist_for_each_entry_safe(this, next, &hb1->chain, list) {
|
| 2122 | if (task_count - nr_wake >= nr_requeue)
|
| 2123 | break;
|
| 2124 |
|
| 2125 | if (!match_futex(&this->key, &key1))
|
| 2126 | continue;
|
| 2127 |
|
| 2128 | |
| 2129 | * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
|
| 2130 | * be paired with each other and no other futex ops.
|
| 2131 | *
|
| 2132 | * We should never be requeueing a futex_q with a pi_state,
|
| 2133 | * which is awaiting a futex_unlock_pi().
|
| 2134 |
|
| 2135 | if ((requeue_pi && !this->rt_waiter) ||
|
| 2136 | (!requeue_pi && this->rt_waiter) ||
|
| 2137 | this->pi_state) {
|
| 2138 | ret = -EINVAL;
|
| 2139 | break;
|
| 2140 | }
|
| 2141 |
|
| 2142 | |
| 2143 | * Wake nr_wake waiters. For requeue_pi, if we acquired the
|
| 2144 | * lock, we already woke the top_waiter. If not, it will be
|
| 2145 | * woken by futex_unlock_pi().
|
| 2146 |
|
| 2147 | if (++task_count <= nr_wake && !requeue_pi) {
|
| 2148 | mark_wake_futex(&wake_q, this);
|
| 2149 | continue;
|
| 2150 | }
|
| 2151 |
|
| 2152 |
|
| 2153 | if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
|
| 2154 | ret = -EINVAL;
|
| 2155 | break;
|
| 2156 | }
|
| 2157 |
|
| 2158 | |
| 2159 | * Requeue nr_requeue waiters and possibly one more in the case
|
| 2160 | * of requeue_pi if we couldn't acquire the lock atomically.
|
| 2161 |
|
| 2162 | if (requeue_pi) {
|
| 2163 | |
| 2164 | * Prepare the waiter to take the rt_mutex. Take a
|
| 2165 | * refcount on the pi_state and store the pointer in
|
| 2166 | * the futex_q object of the waiter.
|
| 2167 |
|
| 2168 | get_pi_state(pi_state);
|
| 2169 | this->pi_state = pi_state;
|
| 2170 | ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
|
| 2171 | this->rt_waiter,
|
| 2172 | this->task);
|
| 2173 | if (ret == 1) {
|
| 2174 | |
| 2175 | * We got the lock. We do neither drop the
|
| 2176 | * refcount on pi_state nor clear
|
| 2177 | * this->pi_state because the waiter needs the
|
| 2178 | * pi_state for cleaning up the user space
|
| 2179 | * value. It will drop the refcount after
|
| 2180 | * doing so.
|
| 2181 |
|
| 2182 | requeue_pi_wake_futex(this, &key2, hb2);
|
| 2183 | continue;
|
| 2184 | } else if (ret) {
|
| 2185 | |
| 2186 | * rt_mutex_start_proxy_lock() detected a
|
| 2187 | * potential deadlock when we tried to queue
|
| 2188 | * that waiter. Drop the pi_state reference
|
| 2189 | * which we took above and remove the pointer
|
| 2190 | * to the state from the waiters futex_q
|
| 2191 | * object.
|
| 2192 |
|
| 2193 | this->pi_state = NULL;
|
| 2194 | put_pi_state(pi_state);
|
| 2195 | |
| 2196 | * We stop queueing more waiters and let user
|
| 2197 | * space deal with the mess.
|
| 2198 |
|
| 2199 | break;
|
| 2200 | }
|
| 2201 | }
|
| 2202 | requeue_futex(this, hb1, hb2, &key2);
|
| 2203 | }
|
| 2204 |
|
| 2205 | |
| 2206 | * We took an extra initial reference to the pi_state either
|
| 2207 | * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We
|
| 2208 | * need to drop it here again.
|
| 2209 |
|
| 2210 | put_pi_state(pi_state);
|
| 2211 |
|
| 2212 | out_unlock:
|
| 2213 | double_unlock_hb(hb1, hb2);
|
| 2214 | wake_up_q(&wake_q);
|
| 2215 | hb_waiters_dec(hb2);
|
| 2216 |
|
| 2217 | out_put_keys:
|
| 2218 | put_futex_key(&key2);
|
| 2219 | out_put_key1:
|
| 2220 | put_futex_key(&key1);
|
| 2221 | out:
|
| 2222 | return ret ? ret : task_count;
|
| 2223 | }
|
| 2224 |
|
| 2225 |
|
| 2226 | static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
|
| 2227 | __acquires(&hb->lock)
|
| 2228 | {
|
| 2229 | struct futex_hash_bucket *hb;
|
| 2230 |
|
| 2231 | hb = hash_futex(&q->key);
|
| 2232 |
|
| 2233 | |
| 2234 | * Increment the counter before taking the lock so that
|
| 2235 | * a potential waker won't miss a to-be-slept task that is
|
| 2236 | * waiting for the spinlock. This is safe as all queue_lock()
|
| 2237 | * users end up calling queue_me(). Similarly, for housekeeping,
|
| 2238 | * decrement the counter at queue_unlock() when some error has
|
| 2239 | * occurred and we don't end up adding the task to the list.
|
| 2240 |
|
| 2241 | hb_waiters_inc(hb);
|
| 2242 |
|
| 2243 | q->lock_ptr = &hb->lock;
|
| 2244 |
|
| 2245 | spin_lock(&hb->lock);
|
| 2246 | return hb;
|
| 2247 | }
|
| 2248 |
|
| 2249 | static inline void
|
| 2250 | queue_unlock(struct futex_hash_bucket *hb)
|
| 2251 | __releases(&hb->lock)
|
| 2252 | {
|
| 2253 | spin_unlock(&hb->lock);
|
| 2254 | hb_waiters_dec(hb);
|
| 2255 | }
|
| 2256 |
|
| 2257 | static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
|
| 2258 | {
|
| 2259 | int prio;
|
| 2260 |
|
| 2261 | |
| 2262 | * The priority used to register this element is
|
| 2263 | * - either the real thread-priority for the real-time threads
|
| 2264 | * (i.e. threads with a priority lower than MAX_RT_PRIO)
|
| 2265 | * - or MAX_RT_PRIO for non-RT threads.
|
| 2266 | * Thus, all RT-threads are woken first in priority order, and
|
| 2267 | * the others are woken last, in FIFO order.
|
| 2268 |
|
| 2269 | prio = min(current->normal_prio, MAX_RT_PRIO);
|
| 2270 |
|
| 2271 | plist_node_init(&q->list, prio);
|
| 2272 | plist_add(&q->list, &hb->chain);
|
| 2273 | q->task = current;
|
| 2274 | }
|
| 2275 |
|
| 2276 | |
| 2277 | * queue_me() - Enqueue the futex_q on the futex_hash_bucket
|
| 2278 | * @q: The futex_q to enqueue
|
| 2279 | * @hb: The destination hash bucket
|
| 2280 | *
|
| 2281 | * The hb->lock must be held by the caller, and is released here. A call to
|
| 2282 | * queue_me() is typically paired with exactly one call to unqueue_me(). The
|
| 2283 | * exceptions involve the PI related operations, which may use unqueue_me_pi()
|
| 2284 | * or nothing if the unqueue is done as part of the wake process and the unqueue
|
| 2285 | * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
|
| 2286 | * an example).
|
| 2287 |
|
| 2288 | static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
|
| 2289 | __releases(&hb->lock)
|
| 2290 | {
|
| 2291 | __queue_me(q, hb);
|
| 2292 | spin_unlock(&hb->lock);
|
| 2293 | }
|
| 2294 |
|
| 2295 | |
| 2296 | * unqueue_me() - Remove the futex_q from its futex_hash_bucket
|
| 2297 | * @q: The futex_q to unqueue
|
| 2298 | *
|
| 2299 | * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
|
| 2300 | * be paired with exactly one earlier call to queue_me().
|
| 2301 | *
|
| 2302 | * Return:
|
| 2303 | * - 1 - if the futex_q was still queued (and we removed unqueued it);
|
| 2304 | * - 0 - if the futex_q was already removed by the waking thread
|
| 2305 |
|
| 2306 | static int unqueue_me(struct futex_q *q)
|
| 2307 | {
|
| 2308 | spinlock_t *lock_ptr;
|
| 2309 | int ret = 0;
|
| 2310 |
|
| 2311 |
|
| 2312 | retry:
|
| 2313 | |
| 2314 | * q->lock_ptr can change between this read and the following spin_lock.
|
| 2315 | * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
|
| 2316 | * optimizing lock_ptr out of the logic below.
|
| 2317 |
|
| 2318 | lock_ptr = READ_ONCE(q->lock_ptr);
|
| 2319 | if (lock_ptr != NULL) {
|
| 2320 | spin_lock(lock_ptr);
|
| 2321 | |
| 2322 | * q->lock_ptr can change between reading it and
|
| 2323 | * spin_lock(), causing us to take the wrong lock. This
|
| 2324 | * corrects the race condition.
|
| 2325 | *
|
| 2326 | * Reasoning goes like this: if we have the wrong lock,
|
| 2327 | * q->lock_ptr must have changed (maybe several times)
|
| 2328 | * between reading it and the spin_lock(). It can
|
| 2329 | * change again after the spin_lock() but only if it was
|
| 2330 | * already changed before the spin_lock(). It cannot,
|
| 2331 | * however, change back to the original value. Therefore
|
| 2332 | * we can detect whether we acquired the correct lock.
|
| 2333 |
|
| 2334 | if (unlikely(lock_ptr != q->lock_ptr)) {
|
| 2335 | spin_unlock(lock_ptr);
|
| 2336 | goto retry;
|
| 2337 | }
|
| 2338 | __unqueue_futex(q);
|
| 2339 |
|
| 2340 | BUG_ON(q->pi_state);
|
| 2341 |
|
| 2342 | spin_unlock(lock_ptr);
|
| 2343 | ret = 1;
|
| 2344 | }
|
| 2345 |
|
| 2346 | return ret;
|
| 2347 | }
|
| 2348 |
|
| 2349 | |
| 2350 | * PI futexes can not be requeued and must remove themself from the
|
| 2351 | * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
|
| 2352 | * and dropped here.
|
| 2353 |
|
| 2354 | static void unqueue_me_pi(struct futex_q *q)
|
| 2355 | __releases(q->lock_ptr)
|
| 2356 | {
|
| 2357 | __unqueue_futex(q);
|
| 2358 |
|
| 2359 | BUG_ON(!q->pi_state);
|
| 2360 | put_pi_state(q->pi_state);
|
| 2361 | q->pi_state = NULL;
|
| 2362 |
|
| 2363 | spin_unlock(q->lock_ptr);
|
| 2364 | }
|
| 2365 |
|
| 2366 | static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
|
| 2367 | struct task_struct *argowner)
|
| 2368 | {
|
| 2369 | struct futex_pi_state *pi_state = q->pi_state;
|
| 2370 | u32 uval, uninitialized_var(curval), newval;
|
| 2371 | struct task_struct *oldowner, *newowner;
|
| 2372 | u32 newtid;
|
| 2373 | int ret, err = 0;
|
| 2374 |
|
| 2375 | lockdep_assert_held(q->lock_ptr);
|
| 2376 |
|
| 2377 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
|
| 2378 |
|
| 2379 | oldowner = pi_state->owner;
|
| 2380 |
|
| 2381 | |
| 2382 | * We are here because either:
|
| 2383 | *
|
| 2384 | * - we stole the lock and pi_state->owner needs updating to reflect
|
| 2385 | * that (@argowner == current),
|
| 2386 | *
|
| 2387 | * or:
|
| 2388 | *
|
| 2389 | * - someone stole our lock and we need to fix things to point to the
|
| 2390 | * new owner (@argowner == NULL).
|
| 2391 | *
|
| 2392 | * Either way, we have to replace the TID in the user space variable.
|
| 2393 | * This must be atomic as we have to preserve the owner died bit here.
|
| 2394 | *
|
| 2395 | * Note: We write the user space value _before_ changing the pi_state
|
| 2396 | * because we can fault here. Imagine swapped out pages or a fork
|
| 2397 | * that marked all the anonymous memory readonly for cow.
|
| 2398 | *
|
| 2399 | * Modifying pi_state _before_ the user space value would leave the
|
| 2400 | * pi_state in an inconsistent state when we fault here, because we
|
| 2401 | * need to drop the locks to handle the fault. This might be observed
|
| 2402 | * in the PID check in lookup_pi_state.
|
| 2403 |
|
| 2404 | retry:
|
| 2405 | if (!argowner) {
|
| 2406 | if (oldowner != current) {
|
| 2407 | |
| 2408 | * We raced against a concurrent self; things are
|
| 2409 | * already fixed up. Nothing to do.
|
| 2410 |
|
| 2411 | ret = 0;
|
| 2412 | goto out_unlock;
|
| 2413 | }
|
| 2414 |
|
| 2415 | if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
|
| 2416 |
|
| 2417 | ret = 0;
|
| 2418 | goto out_unlock;
|
| 2419 | }
|
| 2420 |
|
| 2421 | |
| 2422 | * Since we just failed the trylock; there must be an owner.
|
| 2423 |
|
| 2424 | newowner = rt_mutex_owner(&pi_state->pi_mutex);
|
| 2425 | BUG_ON(!newowner);
|
| 2426 | } else {
|
| 2427 | WARN_ON_ONCE(argowner != current);
|
| 2428 | if (oldowner == current) {
|
| 2429 | |
| 2430 | * We raced against a concurrent self; things are
|
| 2431 | * already fixed up. Nothing to do.
|
| 2432 |
|
| 2433 | ret = 0;
|
| 2434 | goto out_unlock;
|
| 2435 | }
|
| 2436 | newowner = argowner;
|
| 2437 | }
|
| 2438 |
|
| 2439 | newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
|
| 2440 |
|
| 2441 | if (!pi_state->owner)
|
| 2442 | newtid |= FUTEX_OWNER_DIED;
|
| 2443 |
|
| 2444 | err = get_futex_value_locked(&uval, uaddr);
|
| 2445 | if (err)
|
| 2446 | goto handle_err;
|
| 2447 |
|
| 2448 | for (;;) {
|
| 2449 | newval = (uval & FUTEX_OWNER_DIED) | newtid;
|
| 2450 |
|
| 2451 | err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
|
| 2452 | if (err)
|
| 2453 | goto handle_err;
|
| 2454 |
|
| 2455 | if (curval == uval)
|
| 2456 | break;
|
| 2457 | uval = curval;
|
| 2458 | }
|
| 2459 |
|
| 2460 | |
| 2461 | * We fixed up user space. Now we need to fix the pi_state
|
| 2462 | * itself.
|
| 2463 |
|
| 2464 | if (pi_state->owner != NULL) {
|
| 2465 | raw_spin_lock(&pi_state->owner->pi_lock);
|
| 2466 | WARN_ON(list_empty(&pi_state->list));
|
| 2467 | list_del_init(&pi_state->list);
|
| 2468 | raw_spin_unlock(&pi_state->owner->pi_lock);
|
| 2469 | }
|
| 2470 |
|
| 2471 | pi_state->owner = newowner;
|
| 2472 |
|
| 2473 | raw_spin_lock(&newowner->pi_lock);
|
| 2474 | WARN_ON(!list_empty(&pi_state->list));
|
| 2475 | list_add(&pi_state->list, &newowner->pi_state_list);
|
| 2476 | raw_spin_unlock(&newowner->pi_lock);
|
| 2477 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
| 2478 |
|
| 2479 | return 0;
|
| 2480 |
|
| 2481 | |
| 2482 | * In order to reschedule or handle a page fault, we need to drop the
|
| 2483 | * locks here. In the case of a fault, this gives the other task
|
| 2484 | * (either the highest priority waiter itself or the task which stole
|
| 2485 | * the rtmutex) the chance to try the fixup of the pi_state. So once we
|
| 2486 | * are back from handling the fault we need to check the pi_state after
|
| 2487 | * reacquiring the locks and before trying to do another fixup. When
|
| 2488 | * the fixup has been done already we simply return.
|
| 2489 | *
|
| 2490 | * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
|
| 2491 | * drop hb->lock since the caller owns the hb -> futex_q relation.
|
| 2492 | * Dropping the pi_mutex->wait_lock requires the state revalidate.
|
| 2493 |
|
| 2494 | handle_err:
|
| 2495 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
| 2496 | spin_unlock(q->lock_ptr);
|
| 2497 |
|
| 2498 | switch (err) {
|
| 2499 | case -EFAULT:
|
| 2500 | ret = fault_in_user_writeable(uaddr);
|
| 2501 | break;
|
| 2502 |
|
| 2503 | case -EAGAIN:
|
| 2504 | cond_resched();
|
| 2505 | ret = 0;
|
| 2506 | break;
|
| 2507 |
|
| 2508 | default:
|
| 2509 | WARN_ON_ONCE(1);
|
| 2510 | ret = err;
|
| 2511 | break;
|
| 2512 | }
|
| 2513 |
|
| 2514 | spin_lock(q->lock_ptr);
|
| 2515 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
|
| 2516 |
|
| 2517 | |
| 2518 | * Check if someone else fixed it for us:
|
| 2519 |
|
| 2520 | if (pi_state->owner != oldowner) {
|
| 2521 | ret = 0;
|
| 2522 | goto out_unlock;
|
| 2523 | }
|
| 2524 |
|
| 2525 | if (ret)
|
| 2526 | goto out_unlock;
|
| 2527 |
|
| 2528 | goto retry;
|
| 2529 |
|
| 2530 | out_unlock:
|
| 2531 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
| 2532 | return ret;
|
| 2533 | }
|
| 2534 |
|
| 2535 | static long futex_wait_restart(struct restart_block *restart);
|
| 2536 |
|
| 2537 | |
| 2538 | * fixup_owner() - Post lock pi_state and corner case management
|
| 2539 | * @uaddr: user address of the futex
|
| 2540 | * @q: futex_q (contains pi_state and access to the rt_mutex)
|
| 2541 | * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
|
| 2542 | *
|
| 2543 | * After attempting to lock an rt_mutex, this function is called to cleanup
|
| 2544 | * the pi_state owner as well as handle race conditions that may allow us to
|
| 2545 | * acquire the lock. Must be called with the hb lock held.
|
| 2546 | *
|
| 2547 | * Return:
|
| 2548 | * - 1 - success, lock taken;
|
| 2549 | * - 0 - success, lock not taken;
|
| 2550 | * - <0 - on error (-EFAULT)
|
| 2551 |
|
| 2552 | static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
|
| 2553 | {
|
| 2554 | int ret = 0;
|
| 2555 |
|
| 2556 | if (locked) {
|
| 2557 | |
| 2558 | * Got the lock. We might not be the anticipated owner if we
|
| 2559 | * did a lock-steal - fix up the PI-state in that case:
|
| 2560 | *
|
| 2561 | * Speculative pi_state->owner read (we don't hold wait_lock);
|
| 2562 | * since we own the lock pi_state->owner == current is the
|
| 2563 | * stable state, anything else needs more attention.
|
| 2564 |
|
| 2565 | if (q->pi_state->owner != current)
|
| 2566 | ret = fixup_pi_state_owner(uaddr, q, current);
|
| 2567 | goto out;
|
| 2568 | }
|
| 2569 |
|
| 2570 | |
| 2571 | * If we didn't get the lock; check if anybody stole it from us. In
|
| 2572 | * that case, we need to fix up the uval to point to them instead of
|
| 2573 | * us, otherwise bad things happen. [10]
|
| 2574 | *
|
| 2575 | * Another speculative read; pi_state->owner == current is unstable
|
| 2576 | * but needs our attention.
|
| 2577 |
|
| 2578 | if (q->pi_state->owner == current) {
|
| 2579 | ret = fixup_pi_state_owner(uaddr, q, NULL);
|
| 2580 | goto out;
|
| 2581 | }
|
| 2582 |
|
| 2583 | |
| 2584 | * Paranoia check. If we did not take the lock, then we should not be
|
| 2585 | * the owner of the rt_mutex.
|
| 2586 |
|
| 2587 | if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) {
|
| 2588 | printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
|
| 2589 | "pi-state %p\n", ret,
|
| 2590 | q->pi_state->pi_mutex.owner,
|
| 2591 | q->pi_state->owner);
|
| 2592 | }
|
| 2593 |
|
| 2594 | out:
|
| 2595 | return ret ? ret : locked;
|
| 2596 | }
|
| 2597 |
|
| 2598 | |
| 2599 | * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
|
| 2600 | * @hb: the futex hash bucket, must be locked by the caller
|
| 2601 | * @q: the futex_q to queue up on
|
| 2602 | * @timeout: the prepared hrtimer_sleeper, or null for no timeout
|
| 2603 |
|
| 2604 | static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
|
| 2605 | struct hrtimer_sleeper *timeout)
|
| 2606 | {
|
| 2607 | |
| 2608 | * The task state is guaranteed to be set before another task can
|
| 2609 | * wake it. set_current_state() is implemented using smp_store_mb() and
|
| 2610 | * queue_me() calls spin_unlock() upon completion, both serializing
|
| 2611 | * access to the hash list and forcing another memory barrier.
|
| 2612 |
|
| 2613 | set_current_state(TASK_INTERRUPTIBLE);
|
| 2614 | queue_me(q, hb);
|
| 2615 |
|
| 2616 |
|
| 2617 | if (timeout)
|
| 2618 | hrtimer_sleeper_start_expires(timeout, HRTIMER_MODE_ABS);
|
| 2619 |
|
| 2620 | |
| 2621 | * If we have been removed from the hash list, then another task
|
| 2622 | * has tried to wake us, and we can skip the call to schedule().
|
| 2623 |
|
| 2624 | if (likely(!plist_node_empty(&q->list))) {
|
| 2625 | |
| 2626 | * If the timer has already expired, current will already be
|
| 2627 | * flagged for rescheduling. Only call schedule if there
|
| 2628 | * is no timeout, or if it has yet to expire.
|
| 2629 |
|
| 2630 | if (!timeout || timeout->task)
|
| 2631 | freezable_schedule();
|
| 2632 | }
|
| 2633 | __set_current_state(TASK_RUNNING);
|
| 2634 | }
|
| 2635 |
|
| 2636 | |
| 2637 | * futex_wait_setup() - Prepare to wait on a futex
|
| 2638 | * @uaddr: the futex userspace address
|
| 2639 | * @val: the expected value
|
| 2640 | * @flags: futex flags (FLAGS_SHARED, etc.)
|
| 2641 | * @q: the associated futex_q
|
| 2642 | * @hb: storage for hash_bucket pointer to be returned to caller
|
| 2643 | *
|
| 2644 | * Setup the futex_q and locate the hash_bucket. Get the futex value and
|
| 2645 | * compare it with the expected value. Handle atomic faults internally.
|
| 2646 | * Return with the hb lock held and a q.key reference on success, and unlocked
|
| 2647 | * with no q.key reference on failure.
|
| 2648 | *
|
| 2649 | * Return:
|
| 2650 | * - 0 - uaddr contains val and hb has been locked;
|
| 2651 | * - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
|
| 2652 |
|
| 2653 | static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
|
| 2654 | struct futex_q *q, struct futex_hash_bucket **hb)
|
| 2655 | {
|
| 2656 | u32 uval;
|
| 2657 | int ret;
|
| 2658 |
|
| 2659 | |
| 2660 | * Access the page AFTER the hash-bucket is locked.
|
| 2661 | * Order is important:
|
| 2662 | *
|
| 2663 | * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
|
| 2664 | * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
|
| 2665 | *
|
| 2666 | * The basic logical guarantee of a futex is that it blocks ONLY
|
| 2667 | * if cond(var) is known to be true at the time of blocking, for
|
| 2668 | * any cond. If we locked the hash-bucket after testing *uaddr, that
|
| 2669 | * would open a race condition where we could block indefinitely with
|
| 2670 | * cond(var) false, which would violate the guarantee.
|
| 2671 | *
|
| 2672 | * On the other hand, we insert q and release the hash-bucket only
|
| 2673 | * after testing *uaddr. This guarantees that futex_wait() will NOT
|
| 2674 | * absorb a wakeup if *uaddr does not match the desired values
|
| 2675 | * while the syscall executes.
|
| 2676 |
|
| 2677 | retry:
|
| 2678 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ);
|
| 2679 | if (unlikely(ret != 0))
|
| 2680 | return ret;
|
| 2681 |
|
| 2682 | retry_private:
|
| 2683 | *hb = queue_lock(q);
|
| 2684 |
|
| 2685 | ret = get_futex_value_locked(&uval, uaddr);
|
| 2686 |
|
| 2687 | if (ret) {
|
| 2688 | queue_unlock(*hb);
|
| 2689 |
|
| 2690 | ret = get_user(uval, uaddr);
|
| 2691 | if (ret)
|
| 2692 | goto out;
|
| 2693 |
|
| 2694 | if (!(flags & FLAGS_SHARED))
|
| 2695 | goto retry_private;
|
| 2696 |
|
| 2697 | put_futex_key(&q->key);
|
| 2698 | goto retry;
|
| 2699 | }
|
| 2700 |
|
| 2701 | if (uval != val) {
|
| 2702 | queue_unlock(*hb);
|
| 2703 | ret = -EWOULDBLOCK;
|
| 2704 | }
|
| 2705 |
|
| 2706 | out:
|
| 2707 | if (ret)
|
| 2708 | put_futex_key(&q->key);
|
| 2709 | return ret;
|
| 2710 | }
|
| 2711 |
|
| 2712 | static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
|
| 2713 | ktime_t *abs_time, u32 bitset)
|
| 2714 | {
|
| 2715 | struct hrtimer_sleeper timeout, *to;
|
| 2716 | struct restart_block *restart;
|
| 2717 | struct futex_hash_bucket *hb;
|
| 2718 | struct futex_q q = futex_q_init;
|
| 2719 | int ret;
|
| 2720 |
|
| 2721 | if (!bitset)
|
| 2722 | return -EINVAL;
|
| 2723 | q.bitset = bitset;
|
| 2724 |
|
| 2725 | to = futex_setup_timer(abs_time, &timeout, flags,
|
| 2726 | current->timer_slack_ns);
|
| 2727 | retry:
|
| 2728 | |
| 2729 | * Prepare to wait on uaddr. On success, holds hb lock and increments
|
| 2730 | * q.key refs.
|
| 2731 |
|
| 2732 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
|
| 2733 | if (ret)
|
| 2734 | goto out;
|
| 2735 |
|
| 2736 |
|
| 2737 | futex_wait_queue_me(hb, &q, to);
|
| 2738 |
|
| 2739 |
|
| 2740 | ret = 0;
|
| 2741 |
|
| 2742 | if (!unqueue_me(&q))
|
| 2743 | goto out;
|
| 2744 | ret = -ETIMEDOUT;
|
| 2745 | if (to && !to->task)
|
| 2746 | goto out;
|
| 2747 |
|
| 2748 | |
| 2749 | * We expect signal_pending(current), but we might be the
|
| 2750 | * victim of a spurious wakeup as well.
|
| 2751 |
|
| 2752 | if (!signal_pending(current))
|
| 2753 | goto retry;
|
| 2754 |
|
| 2755 | ret = -ERESTARTSYS;
|
| 2756 | if (!abs_time)
|
| 2757 | goto out;
|
| 2758 |
|
| 2759 | restart = ¤t->restart_block;
|
| 2760 | restart->fn = futex_wait_restart;
|
| 2761 | restart->futex.uaddr = uaddr;
|
| 2762 | restart->futex.val = val;
|
| 2763 | restart->futex.time = *abs_time;
|
| 2764 | restart->futex.bitset = bitset;
|
| 2765 | restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
|
| 2766 |
|
| 2767 | ret = -ERESTART_RESTARTBLOCK;
|
| 2768 |
|
| 2769 | out:
|
| 2770 | if (to) {
|
| 2771 | hrtimer_cancel(&to->timer);
|
| 2772 | destroy_hrtimer_on_stack(&to->timer);
|
| 2773 | }
|
| 2774 | return ret;
|
| 2775 | }
|
| 2776 |
|
| 2777 |
|
| 2778 | static long futex_wait_restart(struct restart_block *restart)
|
| 2779 | {
|
| 2780 | u32 __user *uaddr = restart->futex.uaddr;
|
| 2781 | ktime_t t, *tp = NULL;
|
| 2782 |
|
| 2783 | if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
|
| 2784 | t = restart->futex.time;
|
| 2785 | tp = &t;
|
| 2786 | }
|
| 2787 | restart->fn = do_no_restart_syscall;
|
| 2788 |
|
| 2789 | return (long)futex_wait(uaddr, restart->futex.flags,
|
| 2790 | restart->futex.val, tp, restart->futex.bitset);
|
| 2791 | }
|
| 2792 |
|
| 2793 |
|
| 2794 | |
| 2795 | * Userspace tried a 0 -> TID atomic transition of the futex value
|
| 2796 | * and failed. The kernel side here does the whole locking operation:
|
| 2797 | * if there are waiters then it will block as a consequence of relying
|
| 2798 | * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
|
| 2799 | * a 0 value of the futex too.).
|
| 2800 | *
|
| 2801 | * Also serves as futex trylock_pi()'ing, and due semantics.
|
| 2802 |
|
| 2803 | static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
|
| 2804 | ktime_t *time, int trylock)
|
| 2805 | {
|
| 2806 | struct hrtimer_sleeper timeout, *to;
|
| 2807 | struct futex_pi_state *pi_state = NULL;
|
| 2808 | struct task_struct *exiting = NULL;
|
| 2809 | struct rt_mutex_waiter rt_waiter;
|
| 2810 | struct futex_hash_bucket *hb;
|
| 2811 | struct futex_q q = futex_q_init;
|
| 2812 | int res, ret;
|
| 2813 |
|
| 2814 | if (!IS_ENABLED(CONFIG_FUTEX_PI))
|
| 2815 | return -ENOSYS;
|
| 2816 |
|
| 2817 | if (refill_pi_state_cache())
|
| 2818 | return -ENOMEM;
|
| 2819 |
|
| 2820 | to = futex_setup_timer(time, &timeout, FLAGS_CLOCKRT, 0);
|
| 2821 |
|
| 2822 | retry:
|
| 2823 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE);
|
| 2824 | if (unlikely(ret != 0))
|
| 2825 | goto out;
|
| 2826 |
|
| 2827 | retry_private:
|
| 2828 | hb = queue_lock(&q);
|
| 2829 |
|
| 2830 | ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current,
|
| 2831 | &exiting, 0);
|
| 2832 | if (unlikely(ret)) {
|
| 2833 | |
| 2834 | * Atomic work succeeded and we got the lock,
|
| 2835 | * or failed. Either way, we do _not_ block.
|
| 2836 |
|
| 2837 | switch (ret) {
|
| 2838 | case 1:
|
| 2839 |
|
| 2840 | ret = 0;
|
| 2841 | goto out_unlock_put_key;
|
| 2842 | case -EFAULT:
|
| 2843 | goto uaddr_faulted;
|
| 2844 | case -EBUSY:
|
| 2845 | case -EAGAIN:
|
| 2846 | |
| 2847 | * Two reasons for this:
|
| 2848 | * - EBUSY: Task is exiting and we just wait for the
|
| 2849 | * exit to complete.
|
| 2850 | * - EAGAIN: The user space value changed.
|
| 2851 |
|
| 2852 | queue_unlock(hb);
|
| 2853 | put_futex_key(&q.key);
|
| 2854 | |
| 2855 | * Handle the case where the owner is in the middle of
|
| 2856 | * exiting. Wait for the exit to complete otherwise
|
| 2857 | * this task might loop forever, aka. live lock.
|
| 2858 |
|
| 2859 | wait_for_owner_exiting(ret, exiting);
|
| 2860 | cond_resched();
|
| 2861 | goto retry;
|
| 2862 | default:
|
| 2863 | goto out_unlock_put_key;
|
| 2864 | }
|
| 2865 | }
|
| 2866 |
|
| 2867 | WARN_ON(!q.pi_state);
|
| 2868 |
|
| 2869 | |
| 2870 | * Only actually queue now that the atomic ops are done:
|
| 2871 |
|
| 2872 | __queue_me(&q, hb);
|
| 2873 |
|
| 2874 | if (trylock) {
|
| 2875 | ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
|
| 2876 |
|
| 2877 | ret = ret ? 0 : -EWOULDBLOCK;
|
| 2878 | goto no_block;
|
| 2879 | }
|
| 2880 |
|
| 2881 | rt_mutex_init_waiter(&rt_waiter);
|
| 2882 |
|
| 2883 | |
| 2884 | * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
|
| 2885 | * hold it while doing rt_mutex_start_proxy(), because then it will
|
| 2886 | * include hb->lock in the blocking chain, even through we'll not in
|
| 2887 | * fact hold it while blocking. This will lead it to report -EDEADLK
|
| 2888 | * and BUG when futex_unlock_pi() interleaves with this.
|
| 2889 | *
|
| 2890 | * Therefore acquire wait_lock while holding hb->lock, but drop the
|
| 2891 | * latter before calling __rt_mutex_start_proxy_lock(). This
|
| 2892 | * interleaves with futex_unlock_pi() -- which does a similar lock
|
| 2893 | * handoff -- such that the latter can observe the futex_q::pi_state
|
| 2894 | * before __rt_mutex_start_proxy_lock() is done.
|
| 2895 |
|
| 2896 | raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
|
| 2897 | spin_unlock(q.lock_ptr);
|
| 2898 | |
| 2899 | * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
|
| 2900 | * such that futex_unlock_pi() is guaranteed to observe the waiter when
|
| 2901 | * it sees the futex_q::pi_state.
|
| 2902 |
|
| 2903 | ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
|
| 2904 | raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
|
| 2905 |
|
| 2906 | if (ret) {
|
| 2907 | if (ret == 1)
|
| 2908 | ret = 0;
|
| 2909 | goto cleanup;
|
| 2910 | }
|
| 2911 |
|
| 2912 | if (unlikely(to))
|
| 2913 | hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS);
|
| 2914 |
|
| 2915 | ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
|
| 2916 |
|
| 2917 | cleanup:
|
| 2918 | spin_lock(q.lock_ptr);
|
| 2919 | |
| 2920 | * If we failed to acquire the lock (deadlock/signal/timeout), we must
|
| 2921 | * first acquire the hb->lock before removing the lock from the
|
| 2922 | * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
|
| 2923 | * lists consistent.
|
| 2924 | *
|
| 2925 | * In particular; it is important that futex_unlock_pi() can not
|
| 2926 | * observe this inconsistency.
|
| 2927 |
|
| 2928 | if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
|
| 2929 | ret = 0;
|
| 2930 |
|
| 2931 | no_block:
|
| 2932 | |
| 2933 | * Fixup the pi_state owner and possibly acquire the lock if we
|
| 2934 | * haven't already.
|
| 2935 |
|
| 2936 | res = fixup_owner(uaddr, &q, !ret);
|
| 2937 | |
| 2938 | * If fixup_owner() returned an error, proprogate that. If it acquired
|
| 2939 | * the lock, clear our -ETIMEDOUT or -EINTR.
|
| 2940 |
|
| 2941 | if (res)
|
| 2942 | ret = (res < 0) ? res : 0;
|
| 2943 |
|
| 2944 | |
| 2945 | * If fixup_owner() faulted and was unable to handle the fault, unlock
|
| 2946 | * it and return the fault to userspace.
|
| 2947 |
|
| 2948 | if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) {
|
| 2949 | pi_state = q.pi_state;
|
| 2950 | get_pi_state(pi_state);
|
| 2951 | }
|
| 2952 |
|
| 2953 |
|
| 2954 | unqueue_me_pi(&q);
|
| 2955 |
|
| 2956 | if (pi_state) {
|
| 2957 | rt_mutex_futex_unlock(&pi_state->pi_mutex);
|
| 2958 | put_pi_state(pi_state);
|
| 2959 | }
|
| 2960 |
|
| 2961 | goto out_put_key;
|
| 2962 |
|
| 2963 | out_unlock_put_key:
|
| 2964 | queue_unlock(hb);
|
| 2965 |
|
| 2966 | out_put_key:
|
| 2967 | put_futex_key(&q.key);
|
| 2968 | out:
|
| 2969 | if (to) {
|
| 2970 | hrtimer_cancel(&to->timer);
|
| 2971 | destroy_hrtimer_on_stack(&to->timer);
|
| 2972 | }
|
| 2973 | return ret != -EINTR ? ret : -ERESTARTNOINTR;
|
| 2974 |
|
| 2975 | uaddr_faulted:
|
| 2976 | queue_unlock(hb);
|
| 2977 |
|
| 2978 | ret = fault_in_user_writeable(uaddr);
|
| 2979 | if (ret)
|
| 2980 | goto out_put_key;
|
| 2981 |
|
| 2982 | if (!(flags & FLAGS_SHARED))
|
| 2983 | goto retry_private;
|
| 2984 |
|
| 2985 | put_futex_key(&q.key);
|
| 2986 | goto retry;
|
| 2987 | }
|
| 2988 |
|
| 2989 | |
| 2990 | * Userspace attempted a TID -> 0 atomic transition, and failed.
|
| 2991 | * This is the in-kernel slowpath: we look up the PI state (if any),
|
| 2992 | * and do the rt-mutex unlock.
|
| 2993 |
|
| 2994 | static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
|
| 2995 | {
|
| 2996 | u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
|
| 2997 | union futex_key key = FUTEX_KEY_INIT;
|
| 2998 | struct futex_hash_bucket *hb;
|
| 2999 | struct futex_q *top_waiter;
|
| 3000 | int ret;
|
| 3001 |
|
| 3002 | if (!IS_ENABLED(CONFIG_FUTEX_PI))
|
| 3003 | return -ENOSYS;
|
| 3004 |
|
| 3005 | retry:
|
| 3006 | if (get_user(uval, uaddr))
|
| 3007 | return -EFAULT;
|
| 3008 | |
| 3009 | * We release only a lock we actually own:
|
| 3010 |
|
| 3011 | if ((uval & FUTEX_TID_MASK) != vpid)
|
| 3012 | return -EPERM;
|
| 3013 |
|
| 3014 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE);
|
| 3015 | if (ret)
|
| 3016 | return ret;
|
| 3017 |
|
| 3018 | hb = hash_futex(&key);
|
| 3019 | spin_lock(&hb->lock);
|
| 3020 |
|
| 3021 | |
| 3022 | * Check waiters first. We do not trust user space values at
|
| 3023 | * all and we at least want to know if user space fiddled
|
| 3024 | * with the futex value instead of blindly unlocking.
|
| 3025 |
|
| 3026 | top_waiter = futex_top_waiter(hb, &key);
|
| 3027 | if (top_waiter) {
|
| 3028 | struct futex_pi_state *pi_state = top_waiter->pi_state;
|
| 3029 |
|
| 3030 | ret = -EINVAL;
|
| 3031 | if (!pi_state)
|
| 3032 | goto out_unlock;
|
| 3033 |
|
| 3034 | |
| 3035 | * If current does not own the pi_state then the futex is
|
| 3036 | * inconsistent and user space fiddled with the futex value.
|
| 3037 |
|
| 3038 | if (pi_state->owner != current)
|
| 3039 | goto out_unlock;
|
| 3040 |
|
| 3041 | get_pi_state(pi_state);
|
| 3042 | |
| 3043 | * By taking wait_lock while still holding hb->lock, we ensure
|
| 3044 | * there is no point where we hold neither; and therefore
|
| 3045 | * wake_futex_pi() must observe a state consistent with what we
|
| 3046 | * observed.
|
| 3047 | *
|
| 3048 | * In particular; this forces __rt_mutex_start_proxy() to
|
| 3049 | * complete such that we're guaranteed to observe the
|
| 3050 | * rt_waiter. Also see the WARN in wake_futex_pi().
|
| 3051 |
|
| 3052 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
|
| 3053 | spin_unlock(&hb->lock);
|
| 3054 |
|
| 3055 |
|
| 3056 | ret = wake_futex_pi(uaddr, uval, pi_state);
|
| 3057 |
|
| 3058 | put_pi_state(pi_state);
|
| 3059 |
|
| 3060 | |
| 3061 | * Success, we're done! No tricky corner cases.
|
| 3062 |
|
| 3063 | if (!ret)
|
| 3064 | goto out_putkey;
|
| 3065 | |
| 3066 | * The atomic access to the futex value generated a
|
| 3067 | * pagefault, so retry the user-access and the wakeup:
|
| 3068 |
|
| 3069 | if (ret == -EFAULT)
|
| 3070 | goto pi_faulted;
|
| 3071 | |
| 3072 | * A unconditional UNLOCK_PI op raced against a waiter
|
| 3073 | * setting the FUTEX_WAITERS bit. Try again.
|
| 3074 |
|
| 3075 | if (ret == -EAGAIN)
|
| 3076 | goto pi_retry;
|
| 3077 | |
| 3078 | * wake_futex_pi has detected invalid state. Tell user
|
| 3079 | * space.
|
| 3080 |
|
| 3081 | goto out_putkey;
|
| 3082 | }
|
| 3083 |
|
| 3084 | |
| 3085 | * We have no kernel internal state, i.e. no waiters in the
|
| 3086 | * kernel. Waiters which are about to queue themselves are stuck
|
| 3087 | * on hb->lock. So we can safely ignore them. We do neither
|
| 3088 | * preserve the WAITERS bit not the OWNER_DIED one. We are the
|
| 3089 | * owner.
|
| 3090 |
|
| 3091 | if ((ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))) {
|
| 3092 | spin_unlock(&hb->lock);
|
| 3093 | switch (ret) {
|
| 3094 | case -EFAULT:
|
| 3095 | goto pi_faulted;
|
| 3096 |
|
| 3097 | case -EAGAIN:
|
| 3098 | goto pi_retry;
|
| 3099 |
|
| 3100 | default:
|
| 3101 | WARN_ON_ONCE(1);
|
| 3102 | goto out_putkey;
|
| 3103 | }
|
| 3104 | }
|
| 3105 |
|
| 3106 | |
| 3107 | * If uval has changed, let user space handle it.
|
| 3108 |
|
| 3109 | ret = (curval == uval) ? 0 : -EAGAIN;
|
| 3110 |
|
| 3111 | out_unlock:
|
| 3112 | spin_unlock(&hb->lock);
|
| 3113 | out_putkey:
|
| 3114 | put_futex_key(&key);
|
| 3115 | return ret;
|
| 3116 |
|
| 3117 | pi_retry:
|
| 3118 | put_futex_key(&key);
|
| 3119 | cond_resched();
|
| 3120 | goto retry;
|
| 3121 |
|
| 3122 | pi_faulted:
|
| 3123 | put_futex_key(&key);
|
| 3124 |
|
| 3125 | ret = fault_in_user_writeable(uaddr);
|
| 3126 | if (!ret)
|
| 3127 | goto retry;
|
| 3128 |
|
| 3129 | return ret;
|
| 3130 | }
|
| 3131 |
|
| 3132 | |
| 3133 | * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
|
| 3134 | * @hb: the hash_bucket futex_q was original enqueued on
|
| 3135 | * @q: the futex_q woken while waiting to be requeued
|
| 3136 | * @key2: the futex_key of the requeue target futex
|
| 3137 | * @timeout: the timeout associated with the wait (NULL if none)
|
| 3138 | *
|
| 3139 | * Detect if the task was woken on the initial futex as opposed to the requeue
|
| 3140 | * target futex. If so, determine if it was a timeout or a signal that caused
|
| 3141 | * the wakeup and return the appropriate error code to the caller. Must be
|
| 3142 | * called with the hb lock held.
|
| 3143 | *
|
| 3144 | * Return:
|
| 3145 | * - 0 = no early wakeup detected;
|
| 3146 | * - <0 = -ETIMEDOUT or -ERESTARTNOINTR
|
| 3147 |
|
| 3148 | static inline
|
| 3149 | int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
|
| 3150 | struct futex_q *q, union futex_key *key2,
|
| 3151 | struct hrtimer_sleeper *timeout)
|
| 3152 | {
|
| 3153 | int ret = 0;
|
| 3154 |
|
| 3155 | |
| 3156 | * With the hb lock held, we avoid races while we process the wakeup.
|
| 3157 | * We only need to hold hb (and not hb2) to ensure atomicity as the
|
| 3158 | * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
|
| 3159 | * It can't be requeued from uaddr2 to something else since we don't
|
| 3160 | * support a PI aware source futex for requeue.
|
| 3161 |
|
| 3162 | if (!match_futex(&q->key, key2)) {
|
| 3163 | WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
|
| 3164 | |
| 3165 | * We were woken prior to requeue by a timeout or a signal.
|
| 3166 | * Unqueue the futex_q and determine which it was.
|
| 3167 |
|
| 3168 | plist_del(&q->list, &hb->chain);
|
| 3169 | hb_waiters_dec(hb);
|
| 3170 |
|
| 3171 |
|
| 3172 | ret = -EWOULDBLOCK;
|
| 3173 | if (timeout && !timeout->task)
|
| 3174 | ret = -ETIMEDOUT;
|
| 3175 | else if (signal_pending(current))
|
| 3176 | ret = -ERESTARTNOINTR;
|
| 3177 | }
|
| 3178 | return ret;
|
| 3179 | }
|
| 3180 |
|
| 3181 | |
| 3182 | * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
|
| 3183 | * @uaddr: the futex we initially wait on (non-pi)
|
| 3184 | * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
|
| 3185 | * the same type, no requeueing from private to shared, etc.
|
| 3186 | * @val: the expected value of uaddr
|
| 3187 | * @abs_time: absolute timeout
|
| 3188 | * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
|
| 3189 | * @uaddr2: the pi futex we will take prior to returning to user-space
|
| 3190 | *
|
| 3191 | * The caller will wait on uaddr and will be requeued by futex_requeue() to
|
| 3192 | * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
|
| 3193 | * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
|
| 3194 | * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
|
| 3195 | * without one, the pi logic would not know which task to boost/deboost, if
|
| 3196 | * there was a need to.
|
| 3197 | *
|
| 3198 | * We call schedule in futex_wait_queue_me() when we enqueue and return there
|
| 3199 | * via the following--
|
| 3200 | * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
|
| 3201 | * 2) wakeup on uaddr2 after a requeue
|
| 3202 | * 3) signal
|
| 3203 | * 4) timeout
|
| 3204 | *
|
| 3205 | * If 3, cleanup and return -ERESTARTNOINTR.
|
| 3206 | *
|
| 3207 | * If 2, we may then block on trying to take the rt_mutex and return via:
|
| 3208 | * 5) successful lock
|
| 3209 | * 6) signal
|
| 3210 | * 7) timeout
|
| 3211 | * 8) other lock acquisition failure
|
| 3212 | *
|
| 3213 | * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
|
| 3214 | *
|
| 3215 | * If 4 or 7, we cleanup and return with -ETIMEDOUT.
|
| 3216 | *
|
| 3217 | * Return:
|
| 3218 | * - 0 - On success;
|
| 3219 | * - <0 - On error
|
| 3220 |
|
| 3221 | static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
|
| 3222 | u32 val, ktime_t *abs_time, u32 bitset,
|
| 3223 | u32 __user *uaddr2)
|
| 3224 | {
|
| 3225 | struct hrtimer_sleeper timeout, *to;
|
| 3226 | struct futex_pi_state *pi_state = NULL;
|
| 3227 | struct rt_mutex_waiter rt_waiter;
|
| 3228 | struct futex_hash_bucket *hb;
|
| 3229 | union futex_key key2 = FUTEX_KEY_INIT;
|
| 3230 | struct futex_q q = futex_q_init;
|
| 3231 | int res, ret;
|
| 3232 |
|
| 3233 | if (!IS_ENABLED(CONFIG_FUTEX_PI))
|
| 3234 | return -ENOSYS;
|
| 3235 |
|
| 3236 | if (uaddr == uaddr2)
|
| 3237 | return -EINVAL;
|
| 3238 |
|
| 3239 | if (!bitset)
|
| 3240 | return -EINVAL;
|
| 3241 |
|
| 3242 | to = futex_setup_timer(abs_time, &timeout, flags,
|
| 3243 | current->timer_slack_ns);
|
| 3244 |
|
| 3245 | |
| 3246 | * The waiter is allocated on our stack, manipulated by the requeue
|
| 3247 | * code while we sleep on uaddr.
|
| 3248 |
|
| 3249 | rt_mutex_init_waiter(&rt_waiter);
|
| 3250 |
|
| 3251 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
|
| 3252 | if (unlikely(ret != 0))
|
| 3253 | goto out;
|
| 3254 |
|
| 3255 | q.bitset = bitset;
|
| 3256 | q.rt_waiter = &rt_waiter;
|
| 3257 | q.requeue_pi_key = &key2;
|
| 3258 |
|
| 3259 | |
| 3260 | * Prepare to wait on uaddr. On success, increments q.key (key1) ref
|
| 3261 | * count.
|
| 3262 |
|
| 3263 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
|
| 3264 | if (ret)
|
| 3265 | goto out_key2;
|
| 3266 |
|
| 3267 | |
| 3268 | * The check above which compares uaddrs is not sufficient for
|
| 3269 | * shared futexes. We need to compare the keys:
|
| 3270 |
|
| 3271 | if (match_futex(&q.key, &key2)) {
|
| 3272 | queue_unlock(hb);
|
| 3273 | ret = -EINVAL;
|
| 3274 | goto out_put_keys;
|
| 3275 | }
|
| 3276 |
|
| 3277 |
|
| 3278 | futex_wait_queue_me(hb, &q, to);
|
| 3279 |
|
| 3280 | spin_lock(&hb->lock);
|
| 3281 | ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
|
| 3282 | spin_unlock(&hb->lock);
|
| 3283 | if (ret)
|
| 3284 | goto out_put_keys;
|
| 3285 |
|
| 3286 | |
| 3287 | * In order for us to be here, we know our q.key == key2, and since
|
| 3288 | * we took the hb->lock above, we also know that futex_requeue() has
|
| 3289 | * completed and we no longer have to concern ourselves with a wakeup
|
| 3290 | * race with the atomic proxy lock acquisition by the requeue code. The
|
| 3291 | * futex_requeue dropped our key1 reference and incremented our key2
|
| 3292 | * reference count.
|
| 3293 |
|
| 3294 |
|
| 3295 |
|
| 3296 | if (!q.rt_waiter) {
|
| 3297 | |
| 3298 | * Got the lock. We might not be the anticipated owner if we
|
| 3299 | * did a lock-steal - fix up the PI-state in that case.
|
| 3300 |
|
| 3301 | if (q.pi_state && (q.pi_state->owner != current)) {
|
| 3302 | spin_lock(q.lock_ptr);
|
| 3303 | ret = fixup_pi_state_owner(uaddr2, &q, current);
|
| 3304 | if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
|
| 3305 | pi_state = q.pi_state;
|
| 3306 | get_pi_state(pi_state);
|
| 3307 | }
|
| 3308 | |
| 3309 | * Drop the reference to the pi state which
|
| 3310 | * the requeue_pi() code acquired for us.
|
| 3311 |
|
| 3312 | put_pi_state(q.pi_state);
|
| 3313 | spin_unlock(q.lock_ptr);
|
| 3314 | }
|
| 3315 | } else {
|
| 3316 | struct rt_mutex *pi_mutex;
|
| 3317 |
|
| 3318 | |
| 3319 | * We have been woken up by futex_unlock_pi(), a timeout, or a
|
| 3320 | * signal. futex_unlock_pi() will not destroy the lock_ptr nor
|
| 3321 | * the pi_state.
|
| 3322 |
|
| 3323 | WARN_ON(!q.pi_state);
|
| 3324 | pi_mutex = &q.pi_state->pi_mutex;
|
| 3325 | ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
|
| 3326 |
|
| 3327 | spin_lock(q.lock_ptr);
|
| 3328 | if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
|
| 3329 | ret = 0;
|
| 3330 |
|
| 3331 | debug_rt_mutex_free_waiter(&rt_waiter);
|
| 3332 | |
| 3333 | * Fixup the pi_state owner and possibly acquire the lock if we
|
| 3334 | * haven't already.
|
| 3335 |
|
| 3336 | res = fixup_owner(uaddr2, &q, !ret);
|
| 3337 | |
| 3338 | * If fixup_owner() returned an error, proprogate that. If it
|
| 3339 | * acquired the lock, clear -ETIMEDOUT or -EINTR.
|
| 3340 |
|
| 3341 | if (res)
|
| 3342 | ret = (res < 0) ? res : 0;
|
| 3343 |
|
| 3344 | |
| 3345 | * If fixup_pi_state_owner() faulted and was unable to handle
|
| 3346 | * the fault, unlock the rt_mutex and return the fault to
|
| 3347 | * userspace.
|
| 3348 |
|
| 3349 | if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
|
| 3350 | pi_state = q.pi_state;
|
| 3351 | get_pi_state(pi_state);
|
| 3352 | }
|
| 3353 |
|
| 3354 |
|
| 3355 | unqueue_me_pi(&q);
|
| 3356 | }
|
| 3357 |
|
| 3358 | if (pi_state) {
|
| 3359 | rt_mutex_futex_unlock(&pi_state->pi_mutex);
|
| 3360 | put_pi_state(pi_state);
|
| 3361 | }
|
| 3362 |
|
| 3363 | if (ret == -EINTR) {
|
| 3364 | |
| 3365 | * We've already been requeued, but cannot restart by calling
|
| 3366 | * futex_lock_pi() directly. We could restart this syscall, but
|
| 3367 | * it would detect that the user space "val" changed and return
|
| 3368 | * -EWOULDBLOCK. Save the overhead of the restart and return
|
| 3369 | * -EWOULDBLOCK directly.
|
| 3370 |
|
| 3371 | ret = -EWOULDBLOCK;
|
| 3372 | }
|
| 3373 |
|
| 3374 | out_put_keys:
|
| 3375 | put_futex_key(&q.key);
|
| 3376 | out_key2:
|
| 3377 | put_futex_key(&key2);
|
| 3378 |
|
| 3379 | out:
|
| 3380 | if (to) {
|
| 3381 | hrtimer_cancel(&to->timer);
|
| 3382 | destroy_hrtimer_on_stack(&to->timer);
|
| 3383 | }
|
| 3384 | return ret;
|
| 3385 | }
|
| 3386 |
|
| 3387 | |
| 3388 | * Support for robust futexes: the kernel cleans up held futexes at
|
| 3389 | * thread exit time.
|
| 3390 | *
|
| 3391 | * Implementation: user-space maintains a per-thread list of locks it
|
| 3392 | * is holding. Upon do_exit(), the kernel carefully walks this list,
|
| 3393 | * and marks all locks that are owned by this thread with the
|
| 3394 | * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
|
| 3395 | * always manipulated with the lock held, so the list is private and
|
| 3396 | * per-thread. Userspace also maintains a per-thread 'list_op_pending'
|
| 3397 | * field, to allow the kernel to clean up if the thread dies after
|
| 3398 | * acquiring the lock, but just before it could have added itself to
|
| 3399 | * the list. There can only be one such pending lock.
|
| 3400 |
|
| 3401 |
|
| 3402 | |
| 3403 | * sys_set_robust_list() - Set the robust-futex list head of a task
|
| 3404 | * @head: pointer to the list-head
|
| 3405 | * @len: length of the list-head, as userspace expects
|
| 3406 |
|
| 3407 | SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
|
| 3408 | size_t, len)
|
| 3409 | {
|
| 3410 | if (!futex_cmpxchg_enabled)
|
| 3411 | return -ENOSYS;
|
| 3412 | |
| 3413 | * The kernel knows only one size for now:
|
| 3414 |
|
| 3415 | if (unlikely(len != sizeof(*head)))
|
| 3416 | return -EINVAL;
|
| 3417 |
|
| 3418 | current->robust_list = head;
|
| 3419 |
|
| 3420 | return 0;
|
| 3421 | }
|
| 3422 |
|
| 3423 | |
| 3424 | * sys_get_robust_list() - Get the robust-futex list head of a task
|
| 3425 | * @pid: pid of the process [zero for current task]
|
| 3426 | * @head_ptr: pointer to a list-head pointer, the kernel fills it in
|
| 3427 | * @len_ptr: pointer to a length field, the kernel fills in the header size
|
| 3428 |
|
| 3429 | SYSCALL_DEFINE3(get_robust_list, int, pid,
|
| 3430 | struct robust_list_head __user * __user *, head_ptr,
|
| 3431 | size_t __user *, len_ptr)
|
| 3432 | {
|
| 3433 | struct robust_list_head __user *head;
|
| 3434 | unsigned long ret;
|
| 3435 | struct task_struct *p;
|
| 3436 |
|
| 3437 | if (!futex_cmpxchg_enabled)
|
| 3438 | return -ENOSYS;
|
| 3439 |
|
| 3440 | rcu_read_lock();
|
| 3441 |
|
| 3442 | ret = -ESRCH;
|
| 3443 | if (!pid)
|
| 3444 | p = current;
|
| 3445 | else {
|
| 3446 | p = find_task_by_vpid(pid);
|
| 3447 | if (!p)
|
| 3448 | goto err_unlock;
|
| 3449 | }
|
| 3450 |
|
| 3451 | ret = -EPERM;
|
| 3452 | if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
|
| 3453 | goto err_unlock;
|
| 3454 |
|
| 3455 | head = p->robust_list;
|
| 3456 | rcu_read_unlock();
|
| 3457 |
|
| 3458 | if (put_user(sizeof(*head), len_ptr))
|
| 3459 | return -EFAULT;
|
| 3460 | return put_user(head, head_ptr);
|
| 3461 |
|
| 3462 | err_unlock:
|
| 3463 | rcu_read_unlock();
|
| 3464 |
|
| 3465 | return ret;
|
| 3466 | }
|
| 3467 |
|
| 3468 |
|
| 3469 | #define HANDLE_DEATH_PENDING true
|
| 3470 | #define HANDLE_DEATH_LIST false
|
| 3471 |
|
| 3472 | |
| 3473 | * Process a futex-list entry, check whether it's owned by the
|
| 3474 | * dying task, and do notification if so:
|
| 3475 |
|
| 3476 | static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
|
| 3477 | bool pi, bool pending_op)
|
| 3478 | {
|
| 3479 | u32 uval, uninitialized_var(nval), mval;
|
| 3480 | int err;
|
| 3481 |
|
| 3482 |
|
| 3483 | if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0)
|
| 3484 | return -1;
|
| 3485 |
|
| 3486 | retry:
|
| 3487 | if (get_user(uval, uaddr))
|
| 3488 | return -1;
|
| 3489 |
|
| 3490 | |
| 3491 | * Special case for regular (non PI) futexes. The unlock path in
|
| 3492 | * user space has two race scenarios:
|
| 3493 | *
|
| 3494 | * 1. The unlock path releases the user space futex value and
|
| 3495 | * before it can execute the futex() syscall to wake up
|
| 3496 | * waiters it is killed.
|
| 3497 | *
|
| 3498 | * 2. A woken up waiter is killed before it can acquire the
|
| 3499 | * futex in user space.
|
| 3500 | *
|
| 3501 | * In both cases the TID validation below prevents a wakeup of
|
| 3502 | * potential waiters which can cause these waiters to block
|
| 3503 | * forever.
|
| 3504 | *
|
| 3505 | * In both cases the following conditions are met:
|
| 3506 | *
|
| 3507 | * 1) task->robust_list->list_op_pending != NULL
|
| 3508 | * @pending_op == true
|
| 3509 | * 2) User space futex value == 0
|
| 3510 | * 3) Regular futex: @pi == false
|
| 3511 | *
|
| 3512 | * If these conditions are met, it is safe to attempt waking up a
|
| 3513 | * potential waiter without touching the user space futex value and
|
| 3514 | * trying to set the OWNER_DIED bit. The user space futex value is
|
| 3515 | * uncontended and the rest of the user space mutex state is
|
| 3516 | * consistent, so a woken waiter will just take over the
|
| 3517 | * uncontended futex. Setting the OWNER_DIED bit would create
|
| 3518 | * inconsistent state and malfunction of the user space owner died
|
| 3519 | * handling.
|
| 3520 |
|
| 3521 | if (pending_op && !pi && !uval) {
|
| 3522 | futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
|
| 3523 | return 0;
|
| 3524 | }
|
| 3525 |
|
| 3526 | if ((uval & FUTEX_TID_MASK) != task_pid_vnr(curr))
|
| 3527 | return 0;
|
| 3528 |
|
| 3529 | |
| 3530 | * Ok, this dying thread is truly holding a futex
|
| 3531 | * of interest. Set the OWNER_DIED bit atomically
|
| 3532 | * via cmpxchg, and if the value had FUTEX_WAITERS
|
| 3533 | * set, wake up a waiter (if any). (We have to do a
|
| 3534 | * futex_wake() even if OWNER_DIED is already set -
|
| 3535 | * to handle the rare but possible case of recursive
|
| 3536 | * thread-death.) The rest of the cleanup is done in
|
| 3537 | * userspace.
|
| 3538 |
|
| 3539 | mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
|
| 3540 |
|
| 3541 | |
| 3542 | * We are not holding a lock here, but we want to have
|
| 3543 | * the pagefault_disable/enable() protection because
|
| 3544 | * we want to handle the fault gracefully. If the
|
| 3545 | * access fails we try to fault in the futex with R/W
|
| 3546 | * verification via get_user_pages. get_user() above
|
| 3547 | * does not guarantee R/W access. If that fails we
|
| 3548 | * give up and leave the futex locked.
|
| 3549 |
|
| 3550 | if ((err = cmpxchg_futex_value_locked(&nval, uaddr, uval, mval))) {
|
| 3551 | switch (err) {
|
| 3552 | case -EFAULT:
|
| 3553 | if (fault_in_user_writeable(uaddr))
|
| 3554 | return -1;
|
| 3555 | goto retry;
|
| 3556 |
|
| 3557 | case -EAGAIN:
|
| 3558 | cond_resched();
|
| 3559 | goto retry;
|
| 3560 |
|
| 3561 | default:
|
| 3562 | WARN_ON_ONCE(1);
|
| 3563 | return err;
|
| 3564 | }
|
| 3565 | }
|
| 3566 |
|
| 3567 | if (nval != uval)
|
| 3568 | goto retry;
|
| 3569 |
|
| 3570 | |
| 3571 | * Wake robust non-PI futexes here. The wakeup of
|
| 3572 | * PI futexes happens in exit_pi_state():
|
| 3573 |
|
| 3574 | if (!pi && (uval & FUTEX_WAITERS))
|
| 3575 | futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
|
| 3576 |
|
| 3577 | return 0;
|
| 3578 | }
|
| 3579 |
|
| 3580 | |
| 3581 | * Fetch a robust-list pointer. Bit 0 signals PI futexes:
|
| 3582 |
|
| 3583 | static inline int fetch_robust_entry(struct robust_list __user **entry,
|
| 3584 | struct robust_list __user * __user *head,
|
| 3585 | unsigned int *pi)
|
| 3586 | {
|
| 3587 | unsigned long uentry;
|
| 3588 |
|
| 3589 | if (get_user(uentry, (unsigned long __user *)head))
|
| 3590 | return -EFAULT;
|
| 3591 |
|
| 3592 | *entry = (void __user *)(uentry & ~1UL);
|
| 3593 | *pi = uentry & 1;
|
| 3594 |
|
| 3595 | return 0;
|
| 3596 | }
|
| 3597 |
|
| 3598 | |
| 3599 | * Walk curr->robust_list (very carefully, it's a userspace list!)
|
| 3600 | * and mark any locks found there dead, and notify any waiters.
|
| 3601 | *
|
| 3602 | * We silently return on any sign of list-walking problem.
|
| 3603 |
|
| 3604 | static void exit_robust_list(struct task_struct *curr)
|
| 3605 | {
|
| 3606 | struct robust_list_head __user *head = curr->robust_list;
|
| 3607 | struct robust_list __user *entry, *next_entry, *pending;
|
| 3608 | unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
|
| 3609 | unsigned int uninitialized_var(next_pi);
|
| 3610 | unsigned long futex_offset;
|
| 3611 | int rc;
|
| 3612 |
|
| 3613 | if (!futex_cmpxchg_enabled)
|
| 3614 | return;
|
| 3615 |
|
| 3616 | |
| 3617 | * Fetch the list head (which was registered earlier, via
|
| 3618 | * sys_set_robust_list()):
|
| 3619 |
|
| 3620 | if (fetch_robust_entry(&entry, &head->list.next, &pi))
|
| 3621 | return;
|
| 3622 | |
| 3623 | * Fetch the relative futex offset:
|
| 3624 |
|
| 3625 | if (get_user(futex_offset, &head->futex_offset))
|
| 3626 | return;
|
| 3627 | |
| 3628 | * Fetch any possibly pending lock-add first, and handle it
|
| 3629 | * if it exists:
|
| 3630 |
|
| 3631 | if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
|
| 3632 | return;
|
| 3633 |
|
| 3634 | next_entry = NULL;
|
| 3635 | while (entry != &head->list) {
|
| 3636 | |
| 3637 | * Fetch the next entry in the list before calling
|
| 3638 | * handle_futex_death:
|
| 3639 |
|
| 3640 | rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
|
| 3641 | |
| 3642 | * A pending lock might already be on the list, so
|
| 3643 | * don't process it twice:
|
| 3644 |
|
| 3645 | if (entry != pending) {
|
| 3646 | if (handle_futex_death((void __user *)entry + futex_offset,
|
| 3647 | curr, pi, HANDLE_DEATH_LIST))
|
| 3648 | return;
|
| 3649 | }
|
| 3650 | if (rc)
|
| 3651 | return;
|
| 3652 | entry = next_entry;
|
| 3653 | pi = next_pi;
|
| 3654 | |
| 3655 | * Avoid excessively long or circular lists:
|
| 3656 |
|
| 3657 | if (!--limit)
|
| 3658 | break;
|
| 3659 |
|
| 3660 | cond_resched();
|
| 3661 | }
|
| 3662 |
|
| 3663 | if (pending) {
|
| 3664 | handle_futex_death((void __user *)pending + futex_offset,
|
| 3665 | curr, pip, HANDLE_DEATH_PENDING);
|
| 3666 | }
|
| 3667 | }
|
| 3668 |
|
| 3669 | static void futex_cleanup(struct task_struct *tsk)
|
| 3670 | {
|
| 3671 | if (unlikely(tsk->robust_list)) {
|
| 3672 | exit_robust_list(tsk);
|
| 3673 | tsk->robust_list = NULL;
|
| 3674 | }
|
| 3675 |
|
| 3676 | #ifdef CONFIG_COMPAT
|
| 3677 | if (unlikely(tsk->compat_robust_list)) {
|
| 3678 | compat_exit_robust_list(tsk);
|
| 3679 | tsk->compat_robust_list = NULL;
|
| 3680 | }
|
| 3681 | #endif
|
| 3682 |
|
| 3683 | if (unlikely(!list_empty(&tsk->pi_state_list)))
|
| 3684 | exit_pi_state_list(tsk);
|
| 3685 | }
|
| 3686 |
|
| 3687 | |
| 3688 | * futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD
|
| 3689 | * @tsk: task to set the state on
|
| 3690 | *
|
| 3691 | * Set the futex exit state of the task lockless. The futex waiter code
|
| 3692 | * observes that state when a task is exiting and loops until the task has
|
| 3693 | * actually finished the futex cleanup. The worst case for this is that the
|
| 3694 | * waiter runs through the wait loop until the state becomes visible.
|
| 3695 | *
|
| 3696 | * This is called from the recursive fault handling path in do_exit().
|
| 3697 | *
|
| 3698 | * This is best effort. Either the futex exit code has run already or
|
| 3699 | * not. If the OWNER_DIED bit has been set on the futex then the waiter can
|
| 3700 | * take it over. If not, the problem is pushed back to user space. If the
|
| 3701 | * futex exit code did not run yet, then an already queued waiter might
|
| 3702 | * block forever, but there is nothing which can be done about that.
|
| 3703 |
|
| 3704 | void futex_exit_recursive(struct task_struct *tsk)
|
| 3705 | {
|
| 3706 |
|
| 3707 | if (tsk->futex_state == FUTEX_STATE_EXITING)
|
| 3708 | mutex_unlock(&tsk->futex_exit_mutex);
|
| 3709 | tsk->futex_state = FUTEX_STATE_DEAD;
|
| 3710 | }
|
| 3711 |
|
| 3712 | static void futex_cleanup_begin(struct task_struct *tsk)
|
| 3713 | {
|
| 3714 | |
| 3715 | * Prevent various race issues against a concurrent incoming waiter
|
| 3716 | * including live locks by forcing the waiter to block on
|
| 3717 | * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in
|
| 3718 | * attach_to_pi_owner().
|
| 3719 |
|
| 3720 | mutex_lock(&tsk->futex_exit_mutex);
|
| 3721 |
|
| 3722 | |
| 3723 | * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
|
| 3724 | *
|
| 3725 | * This ensures that all subsequent checks of tsk->futex_state in
|
| 3726 | * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
|
| 3727 | * tsk->pi_lock held.
|
| 3728 | *
|
| 3729 | * It guarantees also that a pi_state which was queued right before
|
| 3730 | * the state change under tsk->pi_lock by a concurrent waiter must
|
| 3731 | * be observed in exit_pi_state_list().
|
| 3732 |
|
| 3733 | raw_spin_lock_irq(&tsk->pi_lock);
|
| 3734 | tsk->futex_state = FUTEX_STATE_EXITING;
|
| 3735 | raw_spin_unlock_irq(&tsk->pi_lock);
|
| 3736 | }
|
| 3737 |
|
| 3738 | static void futex_cleanup_end(struct task_struct *tsk, int state)
|
| 3739 | {
|
| 3740 | |
| 3741 | * Lockless store. The only side effect is that an observer might
|
| 3742 | * take another loop until it becomes visible.
|
| 3743 |
|
| 3744 | tsk->futex_state = state;
|
| 3745 | |
| 3746 | * Drop the exit protection. This unblocks waiters which observed
|
| 3747 | * FUTEX_STATE_EXITING to reevaluate the state.
|
| 3748 |
|
| 3749 | mutex_unlock(&tsk->futex_exit_mutex);
|
| 3750 | }
|
| 3751 |
|
| 3752 | void futex_exec_release(struct task_struct *tsk)
|
| 3753 | {
|
| 3754 | |
| 3755 | * The state handling is done for consistency, but in the case of
|
| 3756 | * exec() there is no way to prevent futher damage as the PID stays
|
| 3757 | * the same. But for the unlikely and arguably buggy case that a
|
| 3758 | * futex is held on exec(), this provides at least as much state
|
| 3759 | * consistency protection which is possible.
|
| 3760 |
|
| 3761 | futex_cleanup_begin(tsk);
|
| 3762 | futex_cleanup(tsk);
|
| 3763 | |
| 3764 | * Reset the state to FUTEX_STATE_OK. The task is alive and about
|
| 3765 | * exec a new binary.
|
| 3766 |
|
| 3767 | futex_cleanup_end(tsk, FUTEX_STATE_OK);
|
| 3768 | }
|
| 3769 |
|
| 3770 | void futex_exit_release(struct task_struct *tsk)
|
| 3771 | {
|
| 3772 | futex_cleanup_begin(tsk);
|
| 3773 | futex_cleanup(tsk);
|
| 3774 | futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
|
| 3775 | }
|
| 3776 |
|
| 3777 | long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
|
| 3778 | u32 __user *uaddr2, u32 val2, u32 val3)
|
| 3779 | {
|
| 3780 | int cmd = op & FUTEX_CMD_MASK;
|
| 3781 | unsigned int flags = 0;
|
| 3782 |
|
| 3783 | if (!(op & FUTEX_PRIVATE_FLAG))
|
| 3784 | flags |= FLAGS_SHARED;
|
| 3785 |
|
| 3786 | if (op & FUTEX_CLOCK_REALTIME) {
|
| 3787 | flags |= FLAGS_CLOCKRT;
|
| 3788 | if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \
|
| 3789 | cmd != FUTEX_WAIT_REQUEUE_PI)
|
| 3790 | return -ENOSYS;
|
| 3791 | }
|
| 3792 |
|
| 3793 | switch (cmd) {
|
| 3794 | case FUTEX_LOCK_PI:
|
| 3795 | case FUTEX_UNLOCK_PI:
|
| 3796 | case FUTEX_TRYLOCK_PI:
|
| 3797 | case FUTEX_WAIT_REQUEUE_PI:
|
| 3798 | case FUTEX_CMP_REQUEUE_PI:
|
| 3799 | if (!futex_cmpxchg_enabled)
|
| 3800 | return -ENOSYS;
|
| 3801 | }
|
| 3802 |
|
| 3803 | switch (cmd) {
|
| 3804 | case FUTEX_WAIT:
|
| 3805 | val3 = FUTEX_BITSET_MATCH_ANY;
|
| 3806 |
|
| 3807 | case FUTEX_WAIT_BITSET:
|
| 3808 | return futex_wait(uaddr, flags, val, timeout, val3);
|
| 3809 | case FUTEX_WAKE:
|
| 3810 | val3 = FUTEX_BITSET_MATCH_ANY;
|
| 3811 |
|
| 3812 | case FUTEX_WAKE_BITSET:
|
| 3813 | return futex_wake(uaddr, flags, val, val3);
|
| 3814 | case FUTEX_REQUEUE:
|
| 3815 | return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
|
| 3816 | case FUTEX_CMP_REQUEUE:
|
| 3817 | return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
|
| 3818 | case FUTEX_WAKE_OP:
|
| 3819 | return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
|
| 3820 | case FUTEX_LOCK_PI:
|
| 3821 | return futex_lock_pi(uaddr, flags, timeout, 0);
|
| 3822 | case FUTEX_UNLOCK_PI:
|
| 3823 | return futex_unlock_pi(uaddr, flags);
|
| 3824 | case FUTEX_TRYLOCK_PI:
|
| 3825 | return futex_lock_pi(uaddr, flags, NULL, 1);
|
| 3826 | case FUTEX_WAIT_REQUEUE_PI:
|
| 3827 | val3 = FUTEX_BITSET_MATCH_ANY;
|
| 3828 | return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
|
| 3829 | uaddr2);
|
| 3830 | case FUTEX_CMP_REQUEUE_PI:
|
| 3831 | return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
|
| 3832 | }
|
| 3833 | return -ENOSYS;
|
| 3834 | }
|
| 3835 |
|
| 3836 |
|
| 3837 | SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
|
| 3838 | struct __kernel_timespec __user *, utime, u32 __user *, uaddr2,
|
| 3839 | u32, val3)
|
| 3840 | {
|
| 3841 | struct timespec64 ts;
|
| 3842 | ktime_t t, *tp = NULL;
|
| 3843 | u32 val2 = 0;
|
| 3844 | int cmd = op & FUTEX_CMD_MASK;
|
| 3845 |
|
| 3846 | if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
|
| 3847 | cmd == FUTEX_WAIT_BITSET ||
|
| 3848 | cmd == FUTEX_WAIT_REQUEUE_PI)) {
|
| 3849 | if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
|
| 3850 | return -EFAULT;
|
| 3851 | if (get_timespec64(&ts, utime))
|
| 3852 | return -EFAULT;
|
| 3853 | if (!timespec64_valid(&ts))
|
| 3854 | return -EINVAL;
|
| 3855 |
|
| 3856 | t = timespec64_to_ktime(ts);
|
| 3857 | if (cmd == FUTEX_WAIT)
|
| 3858 | t = ktime_add_safe(ktime_get(), t);
|
| 3859 | tp = &t;
|
| 3860 | }
|
| 3861 | |
| 3862 | * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
|
| 3863 | * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
|
| 3864 |
|
| 3865 | if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
|
| 3866 | cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
|
| 3867 | val2 = (u32) (unsigned long) utime;
|
| 3868 |
|
| 3869 | return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
|
| 3870 | }
|
| 3871 |
|
| 3872 | #ifdef CONFIG_COMPAT
|
| 3873 | |
| 3874 | * Fetch a robust-list pointer. Bit 0 signals PI futexes:
|
| 3875 |
|
| 3876 | static inline int
|
| 3877 | compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
|
| 3878 | compat_uptr_t __user *head, unsigned int *pi)
|
| 3879 | {
|
| 3880 | if (get_user(*uentry, head))
|
| 3881 | return -EFAULT;
|
| 3882 |
|
| 3883 | *entry = compat_ptr((*uentry) & ~1);
|
| 3884 | *pi = (unsigned int)(*uentry) & 1;
|
| 3885 |
|
| 3886 | return 0;
|
| 3887 | }
|
| 3888 |
|
| 3889 | static void __user *futex_uaddr(struct robust_list __user *entry,
|
| 3890 | compat_long_t futex_offset)
|
| 3891 | {
|
| 3892 | compat_uptr_t base = ptr_to_compat(entry);
|
| 3893 | void __user *uaddr = compat_ptr(base + futex_offset);
|
| 3894 |
|
| 3895 | return uaddr;
|
| 3896 | }
|
| 3897 |
|
| 3898 | |
| 3899 | * Walk curr->robust_list (very carefully, it's a userspace list!)
|
| 3900 | * and mark any locks found there dead, and notify any waiters.
|
| 3901 | *
|
| 3902 | * We silently return on any sign of list-walking problem.
|
| 3903 |
|
| 3904 | static void compat_exit_robust_list(struct task_struct *curr)
|
| 3905 | {
|
| 3906 | struct compat_robust_list_head __user *head = curr->compat_robust_list;
|
| 3907 | struct robust_list __user *entry, *next_entry, *pending;
|
| 3908 | unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
|
| 3909 | unsigned int uninitialized_var(next_pi);
|
| 3910 | compat_uptr_t uentry, next_uentry, upending;
|
| 3911 | compat_long_t futex_offset;
|
| 3912 | int rc;
|
| 3913 |
|
| 3914 | if (!futex_cmpxchg_enabled)
|
| 3915 | return;
|
| 3916 |
|
| 3917 | |
| 3918 | * Fetch the list head (which was registered earlier, via
|
| 3919 | * sys_set_robust_list()):
|
| 3920 |
|
| 3921 | if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
|
| 3922 | return;
|
| 3923 | |
| 3924 | * Fetch the relative futex offset:
|
| 3925 |
|
| 3926 | if (get_user(futex_offset, &head->futex_offset))
|
| 3927 | return;
|
| 3928 | |
| 3929 | * Fetch any possibly pending lock-add first, and handle it
|
| 3930 | * if it exists:
|
| 3931 |
|
| 3932 | if (compat_fetch_robust_entry(&upending, &pending,
|
| 3933 | &head->list_op_pending, &pip))
|
| 3934 | return;
|
| 3935 |
|
| 3936 | next_entry = NULL;
|
| 3937 | while (entry != (struct robust_list __user *) &head->list) {
|
| 3938 | |
| 3939 | * Fetch the next entry in the list before calling
|
| 3940 | * handle_futex_death:
|
| 3941 |
|
| 3942 | rc = compat_fetch_robust_entry(&next_uentry, &next_entry,
|
| 3943 | (compat_uptr_t __user *)&entry->next, &next_pi);
|
| 3944 | |
| 3945 | * A pending lock might already be on the list, so
|
| 3946 | * dont process it twice:
|
| 3947 |
|
| 3948 | if (entry != pending) {
|
| 3949 | void __user *uaddr = futex_uaddr(entry, futex_offset);
|
| 3950 |
|
| 3951 | if (handle_futex_death(uaddr, curr, pi,
|
| 3952 | HANDLE_DEATH_LIST))
|
| 3953 | return;
|
| 3954 | }
|
| 3955 | if (rc)
|
| 3956 | return;
|
| 3957 | uentry = next_uentry;
|
| 3958 | entry = next_entry;
|
| 3959 | pi = next_pi;
|
| 3960 | |
| 3961 | * Avoid excessively long or circular lists:
|
| 3962 |
|
| 3963 | if (!--limit)
|
| 3964 | break;
|
| 3965 |
|
| 3966 | cond_resched();
|
| 3967 | }
|
| 3968 | if (pending) {
|
| 3969 | void __user *uaddr = futex_uaddr(pending, futex_offset);
|
| 3970 |
|
| 3971 | handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING);
|
| 3972 | }
|
| 3973 | }
|
| 3974 |
|
| 3975 | COMPAT_SYSCALL_DEFINE2(set_robust_list,
|
| 3976 | struct compat_robust_list_head __user *, head,
|
| 3977 | compat_size_t, len)
|
| 3978 | {
|
| 3979 | if (!futex_cmpxchg_enabled)
|
| 3980 | return -ENOSYS;
|
| 3981 |
|
| 3982 | if (unlikely(len != sizeof(*head)))
|
| 3983 | return -EINVAL;
|
| 3984 |
|
| 3985 | current->compat_robust_list = head;
|
| 3986 |
|
| 3987 | return 0;
|
| 3988 | }
|
| 3989 |
|
| 3990 | COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
|
| 3991 | compat_uptr_t __user *, head_ptr,
|
| 3992 | compat_size_t __user *, len_ptr)
|
| 3993 | {
|
| 3994 | struct compat_robust_list_head __user *head;
|
| 3995 | unsigned long ret;
|
| 3996 | struct task_struct *p;
|
| 3997 |
|
| 3998 | if (!futex_cmpxchg_enabled)
|
| 3999 | return -ENOSYS;
|
| 4000 |
|
| 4001 | rcu_read_lock();
|
| 4002 |
|
| 4003 | ret = -ESRCH;
|
| 4004 | if (!pid)
|
| 4005 | p = current;
|
| 4006 | else {
|
| 4007 | p = find_task_by_vpid(pid);
|
| 4008 | if (!p)
|
| 4009 | goto err_unlock;
|
| 4010 | }
|
| 4011 |
|
| 4012 | ret = -EPERM;
|
| 4013 | if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
|
| 4014 | goto err_unlock;
|
| 4015 |
|
| 4016 | head = p->compat_robust_list;
|
| 4017 | rcu_read_unlock();
|
| 4018 |
|
| 4019 | if (put_user(sizeof(*head), len_ptr))
|
| 4020 | return -EFAULT;
|
| 4021 | return put_user(ptr_to_compat(head), head_ptr);
|
| 4022 |
|
| 4023 | err_unlock:
|
| 4024 | rcu_read_unlock();
|
| 4025 |
|
| 4026 | return ret;
|
| 4027 | }
|
| 4028 | #endif
|
| 4029 |
|
| 4030 | #ifdef CONFIG_COMPAT_32BIT_TIME
|
| 4031 | SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
|
| 4032 | struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
|
| 4033 | u32, val3)
|
| 4034 | {
|
| 4035 | struct timespec64 ts;
|
| 4036 | ktime_t t, *tp = NULL;
|
| 4037 | int val2 = 0;
|
| 4038 | int cmd = op & FUTEX_CMD_MASK;
|
| 4039 |
|
| 4040 | if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
|
| 4041 | cmd == FUTEX_WAIT_BITSET ||
|
| 4042 | cmd == FUTEX_WAIT_REQUEUE_PI)) {
|
| 4043 | if (get_old_timespec32(&ts, utime))
|
| 4044 | return -EFAULT;
|
| 4045 | if (!timespec64_valid(&ts))
|
| 4046 | return -EINVAL;
|
| 4047 |
|
| 4048 | t = timespec64_to_ktime(ts);
|
| 4049 | if (cmd == FUTEX_WAIT)
|
| 4050 | t = ktime_add_safe(ktime_get(), t);
|
| 4051 | tp = &t;
|
| 4052 | }
|
| 4053 | if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
|
| 4054 | cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
|
| 4055 | val2 = (int) (unsigned long) utime;
|
| 4056 |
|
| 4057 | return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
|
| 4058 | }
|
| 4059 | #endif
|
| 4060 |
|
| 4061 | static void __init futex_detect_cmpxchg(void)
|
| 4062 | {
|
| 4063 | #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
|
| 4064 | u32 curval;
|
| 4065 |
|
| 4066 | |
| 4067 | * This will fail and we want it. Some arch implementations do
|
| 4068 | * runtime detection of the futex_atomic_cmpxchg_inatomic()
|
| 4069 | * functionality. We want to know that before we call in any
|
| 4070 | * of the complex code paths. Also we want to prevent
|
| 4071 | * registration of robust lists in that case. NULL is
|
| 4072 | * guaranteed to fault and we get -EFAULT on functional
|
| 4073 | * implementation, the non-functional ones will return
|
| 4074 | * -ENOSYS.
|
| 4075 |
|
| 4076 | if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
|
| 4077 | futex_cmpxchg_enabled = 1;
|
| 4078 | #endif
|
| 4079 | }
|
| 4080 |
|
| 4081 | static int __init futex_init(void)
|
| 4082 | {
|
| 4083 | unsigned int futex_shift;
|
| 4084 | unsigned long i;
|
| 4085 |
|
| 4086 | #if CONFIG_BASE_SMALL
|
| 4087 | futex_hashsize = 16;
|
| 4088 | #else
|
| 4089 | futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
|
| 4090 | #endif
|
| 4091 |
|
| 4092 | futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
|
| 4093 | futex_hashsize, 0,
|
| 4094 | futex_hashsize < 256 ? HASH_SMALL : 0,
|
| 4095 | &futex_shift, NULL,
|
| 4096 | futex_hashsize, futex_hashsize);
|
| 4097 | futex_hashsize = 1UL << futex_shift;
|
| 4098 |
|
| 4099 | futex_detect_cmpxchg();
|
| 4100 |
|
| 4101 | for (i = 0; i < futex_hashsize; i++) {
|
| 4102 | atomic_set(&futex_queues[i].waiters, 0);
|
| 4103 | plist_head_init(&futex_queues[i].chain);
|
| 4104 | spin_lock_init(&futex_queues[i].lock);
|
| 4105 | }
|
| 4106 |
|
| 4107 | return 0;
|
| 4108 | }
|
| 4109 | core_initcall(futex_init);
|