| 1 | |
| 2 | * Fast Userspace Mutexes (which I call "Futexes!").
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| 3 | * (C) Rusty Russell, IBM 2002
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| 4 | *
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| 5 | * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
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| 6 | * (C) Copyright 2003 Red Hat Inc, All Rights Reserved
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| 7 | *
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| 8 | * Removed page pinning, fix privately mapped COW pages and other cleanups
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| 9 | * (C) Copyright 2003, 2004 Jamie Lokier
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| 10 | *
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| 11 | * Robust futex support started by Ingo Molnar
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| 12 | * (C) Copyright 2006 Red Hat Inc, All Rights Reserved
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| 13 | * Thanks to Thomas Gleixner for suggestions, analysis and fixes.
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| 14 | *
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| 15 | * PI-futex support started by Ingo Molnar and Thomas Gleixner
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| 16 | * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <[email protected]>
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| 17 | * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <[email protected]>
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| 18 | *
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| 19 | * PRIVATE futexes by Eric Dumazet
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| 20 | * Copyright (C) 2007 Eric Dumazet <[email protected]>
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| 21 | *
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| 22 | * Requeue-PI support by Darren Hart <[email protected]>
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| 23 | * Copyright (C) IBM Corporation, 2009
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| 24 | * Thanks to Thomas Gleixner for conceptual design and careful reviews.
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| 25 | *
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| 26 | * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
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| 27 | * enough at me, Linus for the original (flawed) idea, Matthew
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| 28 | * Kirkwood for proof-of-concept implementation.
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| 29 | *
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| 30 | * "The futexes are also cursed."
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| 31 | * "But they come in a choice of three flavours!"
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| 32 | *
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| 33 | * This program is free software; you can redistribute it and/or modify
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| 34 | * it under the terms of the GNU General Public License as published by
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| 35 | * the Free Software Foundation; either version 2 of the License, or
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| 36 | * (at your option) any later version.
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| 37 | *
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| 38 | * This program is distributed in the hope that it will be useful,
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| 39 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 40 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 41 | * GNU General Public License for more details.
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| 42 | *
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| 43 | * You should have received a copy of the GNU General Public License
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| 44 | * along with this program; if not, write to the Free Software
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| 45 | * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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| 46 |
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| 47 | #include <linux/slab.h>
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| 48 | #include <linux/poll.h>
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| 49 | #include <linux/fs.h>
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| 50 | #include <linux/file.h>
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| 51 | #include <linux/jhash.h>
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| 52 | #include <linux/init.h>
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| 53 | #include <linux/futex.h>
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| 54 | #include <linux/mount.h>
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| 55 | #include <linux/pagemap.h>
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| 56 | #include <linux/syscalls.h>
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| 57 | #include <linux/signal.h>
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| 58 | #include <linux/export.h>
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| 59 | #include <linux/magic.h>
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| 60 | #include <linux/pid.h>
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| 61 | #include <linux/nsproxy.h>
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| 62 | #include <linux/ptrace.h>
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| 63 | #include <linux/sched/rt.h>
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| 64 | #include <linux/sched/wake_q.h>
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| 65 | #include <linux/sched/mm.h>
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| 66 | #include <linux/hugetlb.h>
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| 67 | #include <linux/freezer.h>
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| 68 | #include <linux/bootmem.h>
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| 69 | #include <linux/fault-inject.h>
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| 70 |
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| 71 | #include <asm/futex.h>
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| 72 |
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| 73 | #include "locking/rtmutex_common.h"
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| 74 |
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| 75 | |
| 76 | * READ this before attempting to hack on futexes!
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| 77 | *
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| 78 | * Basic futex operation and ordering guarantees
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| 79 | * =============================================
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| 80 | *
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| 81 | * The waiter reads the futex value in user space and calls
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| 82 | * futex_wait(). This function computes the hash bucket and acquires
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| 83 | * the hash bucket lock. After that it reads the futex user space value
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| 84 | * again and verifies that the data has not changed. If it has not changed
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| 85 | * it enqueues itself into the hash bucket, releases the hash bucket lock
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| 86 | * and schedules.
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| 87 | *
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| 88 | * The waker side modifies the user space value of the futex and calls
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| 89 | * futex_wake(). This function computes the hash bucket and acquires the
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| 90 | * hash bucket lock. Then it looks for waiters on that futex in the hash
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| 91 | * bucket and wakes them.
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| 92 | *
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| 93 | * In futex wake up scenarios where no tasks are blocked on a futex, taking
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| 94 | * the hb spinlock can be avoided and simply return. In order for this
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| 95 | * optimization to work, ordering guarantees must exist so that the waiter
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| 96 | * being added to the list is acknowledged when the list is concurrently being
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| 97 | * checked by the waker, avoiding scenarios like the following:
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| 98 | *
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| 99 | * CPU 0 CPU 1
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| 100 | * val = *futex;
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| 101 | * sys_futex(WAIT, futex, val);
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| 102 | * futex_wait(futex, val);
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| 103 | * uval = *futex;
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| 104 | * *futex = newval;
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| 105 | * sys_futex(WAKE, futex);
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| 106 | * futex_wake(futex);
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| 107 | * if (queue_empty())
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| 108 | * return;
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| 109 | * if (uval == val)
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| 110 | * lock(hash_bucket(futex));
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| 111 | * queue();
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| 112 | * unlock(hash_bucket(futex));
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| 113 | * schedule();
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| 114 | *
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| 115 | * This would cause the waiter on CPU 0 to wait forever because it
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| 116 | * missed the transition of the user space value from val to newval
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| 117 | * and the waker did not find the waiter in the hash bucket queue.
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| 118 | *
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| 119 | * The correct serialization ensures that a waiter either observes
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| 120 | * the changed user space value before blocking or is woken by a
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| 121 | * concurrent waker:
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| 122 | *
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| 123 | * CPU 0 CPU 1
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| 124 | * val = *futex;
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| 125 | * sys_futex(WAIT, futex, val);
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| 126 | * futex_wait(futex, val);
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| 127 | *
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| 128 | * waiters++; (a)
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| 129 | * smp_mb(); (A) <-- paired with -.
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| 130 | * |
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| 131 | * lock(hash_bucket(futex)); |
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| 132 | * |
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| 133 | * uval = *futex; |
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| 134 | * | *futex = newval;
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| 135 | * | sys_futex(WAKE, futex);
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| 136 | * | futex_wake(futex);
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| 137 | * |
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| 138 | * `--------> smp_mb(); (B)
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| 139 | * if (uval == val)
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| 140 | * queue();
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| 141 | * unlock(hash_bucket(futex));
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| 142 | * schedule(); if (waiters)
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| 143 | * lock(hash_bucket(futex));
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| 144 | * else wake_waiters(futex);
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| 145 | * waiters--; (b) unlock(hash_bucket(futex));
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| 146 | *
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| 147 | * Where (A) orders the waiters increment and the futex value read through
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| 148 | * atomic operations (see hb_waiters_inc) and where (B) orders the write
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| 149 | * to futex and the waiters read -- this is done by the barriers for both
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| 150 | * shared and private futexes in get_futex_key_refs().
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| 151 | *
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| 152 | * This yields the following case (where X:=waiters, Y:=futex):
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| 153 | *
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| 154 | * X = Y = 0
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| 155 | *
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| 156 | * w[X]=1 w[Y]=1
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| 157 | * MB MB
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| 158 | * r[Y]=y r[X]=x
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| 159 | *
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| 160 | * Which guarantees that x==0 && y==0 is impossible; which translates back into
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| 161 | * the guarantee that we cannot both miss the futex variable change and the
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| 162 | * enqueue.
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| 163 | *
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| 164 | * Note that a new waiter is accounted for in (a) even when it is possible that
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| 165 | * the wait call can return error, in which case we backtrack from it in (b).
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| 166 | * Refer to the comment in queue_lock().
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| 167 | *
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| 168 | * Similarly, in order to account for waiters being requeued on another
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| 169 | * address we always increment the waiters for the destination bucket before
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| 170 | * acquiring the lock. It then decrements them again after releasing it -
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| 171 | * the code that actually moves the futex(es) between hash buckets (requeue_futex)
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| 172 | * will do the additional required waiter count housekeeping. This is done for
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| 173 | * double_lock_hb() and double_unlock_hb(), respectively.
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| 174 |
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| 175 |
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| 176 | #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
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| 177 | int __read_mostly futex_cmpxchg_enabled;
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| 178 | #endif
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| 179 |
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| 180 | |
| 181 | * Futex flags used to encode options to functions and preserve them across
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| 182 | * restarts.
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| 183 |
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| 184 | #ifdef CONFIG_MMU
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| 185 | # define FLAGS_SHARED 0x01
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| 186 | #else
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| 187 | |
| 188 | * NOMMU does not have per process address space. Let the compiler optimize
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| 189 | * code away.
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| 190 |
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| 191 | # define FLAGS_SHARED 0x00
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| 192 | #endif
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| 193 | #define FLAGS_CLOCKRT 0x02
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| 194 | #define FLAGS_HAS_TIMEOUT 0x04
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| 195 |
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| 196 | |
| 197 | * Priority Inheritance state:
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| 198 |
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| 199 | struct futex_pi_state {
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| 200 | |
| 201 | * list of 'owned' pi_state instances - these have to be
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| 202 | * cleaned up in do_exit() if the task exits prematurely:
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| 203 |
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| 204 | struct list_head list;
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| 205 |
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| 206 | |
| 207 | * The PI object:
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| 208 |
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| 209 | struct rt_mutex pi_mutex;
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| 210 |
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| 211 | struct task_struct *owner;
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| 212 | atomic_t refcount;
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| 213 |
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| 214 | union futex_key key;
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| 215 | } __randomize_layout;
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| 216 |
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| 217 | |
| 218 | * struct futex_q - The hashed futex queue entry, one per waiting task
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| 219 | * @list: priority-sorted list of tasks waiting on this futex
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| 220 | * @task: the task waiting on the futex
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| 221 | * @lock_ptr: the hash bucket lock
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| 222 | * @key: the key the futex is hashed on
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| 223 | * @pi_state: optional priority inheritance state
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| 224 | * @rt_waiter: rt_waiter storage for use with requeue_pi
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| 225 | * @requeue_pi_key: the requeue_pi target futex key
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| 226 | * @bitset: bitset for the optional bitmasked wakeup
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| 227 | *
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| 228 | * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so
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| 229 | * we can wake only the relevant ones (hashed queues may be shared).
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| 230 | *
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| 231 | * A futex_q has a woken state, just like tasks have TASK_RUNNING.
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| 232 | * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
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| 233 | * The order of wakeup is always to make the first condition true, then
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| 234 | * the second.
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| 235 | *
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| 236 | * PI futexes are typically woken before they are removed from the hash list via
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| 237 | * the rt_mutex code. See unqueue_me_pi().
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| 238 |
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| 239 | struct futex_q {
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| 240 | struct plist_node list;
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| 241 |
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| 242 | struct task_struct *task;
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| 243 | spinlock_t *lock_ptr;
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| 244 | union futex_key key;
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| 245 | struct futex_pi_state *pi_state;
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| 246 | struct rt_mutex_waiter *rt_waiter;
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| 247 | union futex_key *requeue_pi_key;
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| 248 | u32 bitset;
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| 249 | } __randomize_layout;
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| 250 |
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| 251 | static const struct futex_q futex_q_init = {
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| 252 |
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| 253 | .key = FUTEX_KEY_INIT,
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| 254 | .bitset = FUTEX_BITSET_MATCH_ANY
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| 255 | };
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| 256 |
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| 257 | |
| 258 | * Hash buckets are shared by all the futex_keys that hash to the same
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| 259 | * location. Each key may have multiple futex_q structures, one for each task
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| 260 | * waiting on a futex.
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| 261 |
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| 262 | struct futex_hash_bucket {
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| 263 | atomic_t waiters;
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| 264 | spinlock_t lock;
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| 265 | struct plist_head chain;
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| 266 | } ____cacheline_aligned_in_smp;
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| 267 |
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| 268 | |
| 269 | * The base of the bucket array and its size are always used together
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| 270 | * (after initialization only in hash_futex()), so ensure that they
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| 271 | * reside in the same cacheline.
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| 272 |
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| 273 | static struct {
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| 274 | struct futex_hash_bucket *queues;
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| 275 | unsigned long hashsize;
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| 276 | } __futex_data __read_mostly __aligned(2*sizeof(long));
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| 277 | #define futex_queues (__futex_data.queues)
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| 278 | #define futex_hashsize (__futex_data.hashsize)
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| 279 |
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| 280 |
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| 281 | |
| 282 | * Fault injections for futexes.
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| 283 |
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| 284 | #ifdef CONFIG_FAIL_FUTEX
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| 285 |
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| 286 | static struct {
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| 287 | struct fault_attr attr;
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| 288 |
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| 289 | bool ignore_private;
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| 290 | } fail_futex = {
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| 291 | .attr = FAULT_ATTR_INITIALIZER,
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| 292 | .ignore_private = false,
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| 293 | };
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| 294 |
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| 295 | static int __init setup_fail_futex(char *str)
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| 296 | {
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| 297 | return setup_fault_attr(&fail_futex.attr, str);
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| 298 | }
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| 299 | __setup("fail_futex=", setup_fail_futex);
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| 300 |
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| 301 | static bool should_fail_futex(bool fshared)
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| 302 | {
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| 303 | if (fail_futex.ignore_private && !fshared)
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| 304 | return false;
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| 305 |
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| 306 | return should_fail(&fail_futex.attr, 1);
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| 307 | }
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| 308 |
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| 309 | #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
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| 310 |
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| 311 | static int __init fail_futex_debugfs(void)
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| 312 | {
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| 313 | umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
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| 314 | struct dentry *dir;
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| 315 |
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| 316 | dir = fault_create_debugfs_attr("fail_futex", NULL,
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| 317 | &fail_futex.attr);
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| 318 | if (IS_ERR(dir))
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| 319 | return PTR_ERR(dir);
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| 320 |
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| 321 | if (!debugfs_create_bool("ignore-private", mode, dir,
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| 322 | &fail_futex.ignore_private)) {
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| 323 | debugfs_remove_recursive(dir);
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| 324 | return -ENOMEM;
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| 325 | }
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| 326 |
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| 327 | return 0;
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| 328 | }
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| 329 |
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| 330 | late_initcall(fail_futex_debugfs);
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| 331 |
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| 332 | #endif
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| 333 |
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| 334 | #else
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| 335 | static inline bool should_fail_futex(bool fshared)
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| 336 | {
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| 337 | return false;
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| 338 | }
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| 339 | #endif
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| 340 |
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| 341 | static inline void futex_get_mm(union futex_key *key)
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| 342 | {
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| 343 | mmgrab(key->private.mm);
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| 344 | |
| 345 | * Ensure futex_get_mm() implies a full barrier such that
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| 346 | * get_futex_key() implies a full barrier. This is relied upon
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| 347 | * as smp_mb(); (B), see the ordering comment above.
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| 348 |
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| 349 | smp_mb__after_atomic();
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| 350 | }
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| 351 |
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| 352 | |
| 353 | * Reflects a new waiter being added to the waitqueue.
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| 354 |
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| 355 | static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
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| 356 | {
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| 357 | #ifdef CONFIG_SMP
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| 358 | atomic_inc(&hb->waiters);
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| 359 | |
| 360 | * Full barrier (A), see the ordering comment above.
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| 361 |
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| 362 | smp_mb__after_atomic();
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| 363 | #endif
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| 364 | }
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| 365 |
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| 366 | |
| 367 | * Reflects a waiter being removed from the waitqueue by wakeup
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| 368 | * paths.
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| 369 |
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| 370 | static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
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| 371 | {
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| 372 | #ifdef CONFIG_SMP
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| 373 | atomic_dec(&hb->waiters);
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| 374 | #endif
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| 375 | }
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| 376 |
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| 377 | static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
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| 378 | {
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| 379 | #ifdef CONFIG_SMP
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| 380 | return atomic_read(&hb->waiters);
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| 381 | #else
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| 382 | return 1;
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| 383 | #endif
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| 384 | }
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| 385 |
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| 386 | |
| 387 | * hash_futex - Return the hash bucket in the global hash
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| 388 | * @key: Pointer to the futex key for which the hash is calculated
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| 389 | *
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| 390 | * We hash on the keys returned from get_futex_key (see below) and return the
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| 391 | * corresponding hash bucket in the global hash.
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| 392 |
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| 393 | static struct futex_hash_bucket *hash_futex(union futex_key *key)
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| 394 | {
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| 395 | u32 hash = jhash2((u32*)&key->both.word,
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| 396 | (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
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| 397 | key->both.offset);
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| 398 | return &futex_queues[hash & (futex_hashsize - 1)];
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| 399 | }
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| 400 |
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| 401 |
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| 402 | |
| 403 | * match_futex - Check whether two futex keys are equal
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| 404 | * @key1: Pointer to key1
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| 405 | * @key2: Pointer to key2
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| 406 | *
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| 407 | * Return 1 if two futex_keys are equal, 0 otherwise.
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| 408 |
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| 409 | static inline int match_futex(union futex_key *key1, union futex_key *key2)
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| 410 | {
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| 411 | return (key1 && key2
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| 412 | && key1->both.word == key2->both.word
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| 413 | && key1->both.ptr == key2->both.ptr
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| 414 | && key1->both.offset == key2->both.offset);
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| 415 | }
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| 416 |
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| 417 | |
| 418 | * Take a reference to the resource addressed by a key.
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| 419 | * Can be called while holding spinlocks.
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| 420 | *
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| 421 |
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| 422 | static void get_futex_key_refs(union futex_key *key)
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| 423 | {
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| 424 | if (!key->both.ptr)
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| 425 | return;
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| 426 |
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| 427 | |
| 428 | * On MMU less systems futexes are always "private" as there is no per
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| 429 | * process address space. We need the smp wmb nevertheless - yes,
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| 430 | * arch/blackfin has MMU less SMP ...
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| 431 |
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| 432 | if (!IS_ENABLED(CONFIG_MMU)) {
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| 433 | smp_mb();
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| 434 | return;
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| 435 | }
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| 436 |
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| 437 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
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| 438 | case FUT_OFF_INODE:
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| 439 | ihold(key->shared.inode);
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| 440 | break;
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| 441 | case FUT_OFF_MMSHARED:
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| 442 | futex_get_mm(key);
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| 443 | break;
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| 444 | default:
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| 445 | |
| 446 | * Private futexes do not hold reference on an inode or
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| 447 | * mm, therefore the only purpose of calling get_futex_key_refs
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| 448 | * is because we need the barrier for the lockless waiter check.
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| 449 |
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| 450 | smp_mb();
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| 451 | }
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| 452 | }
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| 453 |
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| 454 | |
| 455 | * Drop a reference to the resource addressed by a key.
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| 456 | * The hash bucket spinlock must not be held. This is
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| 457 | * a no-op for private futexes, see comment in the get
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| 458 | * counterpart.
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| 459 |
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| 460 | static void drop_futex_key_refs(union futex_key *key)
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| 461 | {
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| 462 | if (!key->both.ptr) {
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| 463 |
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| 464 | WARN_ON_ONCE(1);
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| 465 | return;
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| 466 | }
|
| 467 |
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| 468 | if (!IS_ENABLED(CONFIG_MMU))
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| 469 | return;
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| 470 |
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| 471 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
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| 472 | case FUT_OFF_INODE:
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| 473 | iput(key->shared.inode);
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| 474 | break;
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| 475 | case FUT_OFF_MMSHARED:
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| 476 | mmdrop(key->private.mm);
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| 477 | break;
|
| 478 | }
|
| 479 | }
|
| 480 |
|
| 481 | |
| 482 | * get_futex_key() - Get parameters which are the keys for a futex
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| 483 | * @uaddr: virtual address of the futex
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| 484 | * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
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| 485 | * @key: address where result is stored.
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| 486 | * @rw: mapping needs to be read/write (values: VERIFY_READ,
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| 487 | * VERIFY_WRITE)
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| 488 | *
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| 489 | * Return: a negative error code or 0
|
| 490 | *
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| 491 | * The key words are stored in @key on success.
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| 492 | *
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| 493 | * For shared mappings, it's (page->index, file_inode(vma->vm_file),
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| 494 | * offset_within_page). For private mappings, it's (uaddr, current->mm).
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| 495 | * We can usually work out the index without swapping in the page.
|
| 496 | *
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| 497 | * lock_page() might sleep, the caller should not hold a spinlock.
|
| 498 |
|
| 499 | static int
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| 500 | get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
|
| 501 | {
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| 502 | unsigned long address = (unsigned long)uaddr;
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| 503 | struct mm_struct *mm = current->mm;
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| 504 | struct page *page, *tail;
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| 505 | struct address_space *mapping;
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| 506 | int err, ro = 0;
|
| 507 |
|
| 508 | |
| 509 | * The futex address must be "naturally" aligned.
|
| 510 |
|
| 511 | key->both.offset = address % PAGE_SIZE;
|
| 512 | if (unlikely((address % sizeof(u32)) != 0))
|
| 513 | return -EINVAL;
|
| 514 | address -= key->both.offset;
|
| 515 |
|
| 516 | if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
|
| 517 | return -EFAULT;
|
| 518 |
|
| 519 | if (unlikely(should_fail_futex(fshared)))
|
| 520 | return -EFAULT;
|
| 521 |
|
| 522 | |
| 523 | * PROCESS_PRIVATE futexes are fast.
|
| 524 | * As the mm cannot disappear under us and the 'key' only needs
|
| 525 | * virtual address, we dont even have to find the underlying vma.
|
| 526 | * Note : We do have to check 'uaddr' is a valid user address,
|
| 527 | * but access_ok() should be faster than find_vma()
|
| 528 |
|
| 529 | if (!fshared) {
|
| 530 | key->private.mm = mm;
|
| 531 | key->private.address = address;
|
| 532 | get_futex_key_refs(key);
|
| 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, 1, &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 == VERIFY_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 | get_futex_key_refs(key);
|
| 636 |
|
| 637 | } else {
|
| 638 | struct inode *inode;
|
| 639 |
|
| 640 | |
| 641 | * The associated futex object in this case is the inode and
|
| 642 | * the page->mapping must be traversed. Ordinarily this should
|
| 643 | * be stabilised under page lock but it's not strictly
|
| 644 | * necessary in this case as we just want to pin the inode, not
|
| 645 | * update the radix tree or anything like that.
|
| 646 | *
|
| 647 | * The RCU read lock is taken as the inode is finally freed
|
| 648 | * under RCU. If the mapping still matches expectations then the
|
| 649 | * mapping->host can be safely accessed as being a valid inode.
|
| 650 |
|
| 651 | rcu_read_lock();
|
| 652 |
|
| 653 | if (READ_ONCE(page->mapping) != mapping) {
|
| 654 | rcu_read_unlock();
|
| 655 | put_page(page);
|
| 656 |
|
| 657 | goto again;
|
| 658 | }
|
| 659 |
|
| 660 | inode = READ_ONCE(mapping->host);
|
| 661 | if (!inode) {
|
| 662 | rcu_read_unlock();
|
| 663 | put_page(page);
|
| 664 |
|
| 665 | goto again;
|
| 666 | }
|
| 667 |
|
| 668 | |
| 669 | * Take a reference unless it is about to be freed. Previously
|
| 670 | * this reference was taken by ihold under the page lock
|
| 671 | * pinning the inode in place so i_lock was unnecessary. The
|
| 672 | * only way for this check to fail is if the inode was
|
| 673 | * truncated in parallel which is almost certainly an
|
| 674 | * application bug. In such a case, just retry.
|
| 675 | *
|
| 676 | * We are not calling into get_futex_key_refs() in file-backed
|
| 677 | * cases, therefore a successful atomic_inc return below will
|
| 678 | * guarantee that get_futex_key() will still imply smp_mb(); (B).
|
| 679 |
|
| 680 | if (!atomic_inc_not_zero(&inode->i_count)) {
|
| 681 | rcu_read_unlock();
|
| 682 | put_page(page);
|
| 683 |
|
| 684 | goto again;
|
| 685 | }
|
| 686 |
|
| 687 |
|
| 688 | if (WARN_ON_ONCE(inode->i_mapping != mapping)) {
|
| 689 | err = -EFAULT;
|
| 690 | rcu_read_unlock();
|
| 691 | iput(inode);
|
| 692 |
|
| 693 | goto out;
|
| 694 | }
|
| 695 |
|
| 696 | key->both.offset |= FUT_OFF_INODE;
|
| 697 | key->shared.inode = inode;
|
| 698 | key->shared.pgoff = basepage_index(tail);
|
| 699 | rcu_read_unlock();
|
| 700 | }
|
| 701 |
|
| 702 | out:
|
| 703 | put_page(page);
|
| 704 | return err;
|
| 705 | }
|
| 706 |
|
| 707 | static inline void put_futex_key(union futex_key *key)
|
| 708 | {
|
| 709 | drop_futex_key_refs(key);
|
| 710 | }
|
| 711 |
|
| 712 | |
| 713 | * fault_in_user_writeable() - Fault in user address and verify RW access
|
| 714 | * @uaddr: pointer to faulting user space address
|
| 715 | *
|
| 716 | * Slow path to fixup the fault we just took in the atomic write
|
| 717 | * access to @uaddr.
|
| 718 | *
|
| 719 | * We have no generic implementation of a non-destructive write to the
|
| 720 | * user address. We know that we faulted in the atomic pagefault
|
| 721 | * disabled section so we can as well avoid the #PF overhead by
|
| 722 | * calling get_user_pages() right away.
|
| 723 |
|
| 724 | static int fault_in_user_writeable(u32 __user *uaddr)
|
| 725 | {
|
| 726 | struct mm_struct *mm = current->mm;
|
| 727 | int ret;
|
| 728 |
|
| 729 | down_read(&mm->mmap_sem);
|
| 730 | ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
|
| 731 | FAULT_FLAG_WRITE, NULL);
|
| 732 | up_read(&mm->mmap_sem);
|
| 733 |
|
| 734 | return ret < 0 ? ret : 0;
|
| 735 | }
|
| 736 |
|
| 737 | |
| 738 | * futex_top_waiter() - Return the highest priority waiter on a futex
|
| 739 | * @hb: the hash bucket the futex_q's reside in
|
| 740 | * @key: the futex key (to distinguish it from other futex futex_q's)
|
| 741 | *
|
| 742 | * Must be called with the hb lock held.
|
| 743 |
|
| 744 | static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
|
| 745 | union futex_key *key)
|
| 746 | {
|
| 747 | struct futex_q *this;
|
| 748 |
|
| 749 | plist_for_each_entry(this, &hb->chain, list) {
|
| 750 | if (match_futex(&this->key, key))
|
| 751 | return this;
|
| 752 | }
|
| 753 | return NULL;
|
| 754 | }
|
| 755 |
|
| 756 | static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
|
| 757 | u32 uval, u32 newval)
|
| 758 | {
|
| 759 | int ret;
|
| 760 |
|
| 761 | pagefault_disable();
|
| 762 | ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
|
| 763 | pagefault_enable();
|
| 764 |
|
| 765 | return ret;
|
| 766 | }
|
| 767 |
|
| 768 | static int get_futex_value_locked(u32 *dest, u32 __user *from)
|
| 769 | {
|
| 770 | int ret;
|
| 771 |
|
| 772 | pagefault_disable();
|
| 773 | ret = __get_user(*dest, from);
|
| 774 | pagefault_enable();
|
| 775 |
|
| 776 | return ret ? -EFAULT : 0;
|
| 777 | }
|
| 778 |
|
| 779 |
|
| 780 | |
| 781 | * PI code:
|
| 782 |
|
| 783 | static int refill_pi_state_cache(void)
|
| 784 | {
|
| 785 | struct futex_pi_state *pi_state;
|
| 786 |
|
| 787 | if (likely(current->pi_state_cache))
|
| 788 | return 0;
|
| 789 |
|
| 790 | pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
|
| 791 |
|
| 792 | if (!pi_state)
|
| 793 | return -ENOMEM;
|
| 794 |
|
| 795 | INIT_LIST_HEAD(&pi_state->list);
|
| 796 |
|
| 797 | pi_state->owner = NULL;
|
| 798 | atomic_set(&pi_state->refcount, 1);
|
| 799 | pi_state->key = FUTEX_KEY_INIT;
|
| 800 |
|
| 801 | current->pi_state_cache = pi_state;
|
| 802 |
|
| 803 | return 0;
|
| 804 | }
|
| 805 |
|
| 806 | static struct futex_pi_state *alloc_pi_state(void)
|
| 807 | {
|
| 808 | struct futex_pi_state *pi_state = current->pi_state_cache;
|
| 809 |
|
| 810 | WARN_ON(!pi_state);
|
| 811 | current->pi_state_cache = NULL;
|
| 812 |
|
| 813 | return pi_state;
|
| 814 | }
|
| 815 |
|
| 816 | static void get_pi_state(struct futex_pi_state *pi_state)
|
| 817 | {
|
| 818 | WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount));
|
| 819 | }
|
| 820 |
|
| 821 | |
| 822 | * Drops a reference to the pi_state object and frees or caches it
|
| 823 | * when the last reference is gone.
|
| 824 | *
|
| 825 | * Must be called with the hb lock held.
|
| 826 |
|
| 827 | static void put_pi_state(struct futex_pi_state *pi_state)
|
| 828 | {
|
| 829 | if (!pi_state)
|
| 830 | return;
|
| 831 |
|
| 832 | if (!atomic_dec_and_test(&pi_state->refcount))
|
| 833 | return;
|
| 834 |
|
| 835 | |
| 836 | * If pi_state->owner is NULL, the owner is most probably dying
|
| 837 | * and has cleaned up the pi_state already
|
| 838 |
|
| 839 | if (pi_state->owner) {
|
| 840 | raw_spin_lock_irq(&pi_state->owner->pi_lock);
|
| 841 | list_del_init(&pi_state->list);
|
| 842 | raw_spin_unlock_irq(&pi_state->owner->pi_lock);
|
| 843 |
|
| 844 | rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
|
| 845 | }
|
| 846 |
|
| 847 | if (current->pi_state_cache)
|
| 848 | kfree(pi_state);
|
| 849 | else {
|
| 850 | |
| 851 | * pi_state->list is already empty.
|
| 852 | * clear pi_state->owner.
|
| 853 | * refcount is at 0 - put it back to 1.
|
| 854 |
|
| 855 | pi_state->owner = NULL;
|
| 856 | atomic_set(&pi_state->refcount, 1);
|
| 857 | current->pi_state_cache = pi_state;
|
| 858 | }
|
| 859 | }
|
| 860 |
|
| 861 | |
| 862 | * Look up the task based on what TID userspace gave us.
|
| 863 | * We dont trust it.
|
| 864 |
|
| 865 | static struct task_struct *futex_find_get_task(pid_t pid)
|
| 866 | {
|
| 867 | struct task_struct *p;
|
| 868 |
|
| 869 | rcu_read_lock();
|
| 870 | p = find_task_by_vpid(pid);
|
| 871 | if (p)
|
| 872 | get_task_struct(p);
|
| 873 |
|
| 874 | rcu_read_unlock();
|
| 875 |
|
| 876 | return p;
|
| 877 | }
|
| 878 |
|
| 879 | |
| 880 | * This task is holding PI mutexes at exit time => bad.
|
| 881 | * Kernel cleans up PI-state, but userspace is likely hosed.
|
| 882 | * (Robust-futex cleanup is separate and might save the day for userspace.)
|
| 883 |
|
| 884 | void exit_pi_state_list(struct task_struct *curr)
|
| 885 | {
|
| 886 | struct list_head *next, *head = &curr->pi_state_list;
|
| 887 | struct futex_pi_state *pi_state;
|
| 888 | struct futex_hash_bucket *hb;
|
| 889 | union futex_key key = FUTEX_KEY_INIT;
|
| 890 |
|
| 891 | if (!futex_cmpxchg_enabled)
|
| 892 | return;
|
| 893 | |
| 894 | * We are a ZOMBIE and nobody can enqueue itself on
|
| 895 | * pi_state_list anymore, but we have to be careful
|
| 896 | * versus waiters unqueueing themselves:
|
| 897 |
|
| 898 | raw_spin_lock_irq(&curr->pi_lock);
|
| 899 | while (!list_empty(head)) {
|
| 900 |
|
| 901 | next = head->next;
|
| 902 | pi_state = list_entry(next, struct futex_pi_state, list);
|
| 903 | key = pi_state->key;
|
| 904 | hb = hash_futex(&key);
|
| 905 | raw_spin_unlock_irq(&curr->pi_lock);
|
| 906 |
|
| 907 | spin_lock(&hb->lock);
|
| 908 |
|
| 909 | raw_spin_lock_irq(&curr->pi_lock);
|
| 910 | |
| 911 | * We dropped the pi-lock, so re-check whether this
|
| 912 | * task still owns the PI-state:
|
| 913 |
|
| 914 | if (head->next != next) {
|
| 915 | spin_unlock(&hb->lock);
|
| 916 | continue;
|
| 917 | }
|
| 918 |
|
| 919 | WARN_ON(pi_state->owner != curr);
|
| 920 | WARN_ON(list_empty(&pi_state->list));
|
| 921 | list_del_init(&pi_state->list);
|
| 922 | pi_state->owner = NULL;
|
| 923 | raw_spin_unlock_irq(&curr->pi_lock);
|
| 924 |
|
| 925 | get_pi_state(pi_state);
|
| 926 | spin_unlock(&hb->lock);
|
| 927 |
|
| 928 | rt_mutex_futex_unlock(&pi_state->pi_mutex);
|
| 929 | put_pi_state(pi_state);
|
| 930 |
|
| 931 | raw_spin_lock_irq(&curr->pi_lock);
|
| 932 | }
|
| 933 | raw_spin_unlock_irq(&curr->pi_lock);
|
| 934 | }
|
| 935 |
|
| 936 | |
| 937 | * We need to check the following states:
|
| 938 | *
|
| 939 | * Waiter | pi_state | pi->owner | uTID | uODIED | ?
|
| 940 | *
|
| 941 | * [1] NULL | --- | --- | 0 | 0/1 | Valid
|
| 942 | * [2] NULL | --- | --- | >0 | 0/1 | Valid
|
| 943 | *
|
| 944 | * [3] Found | NULL | -- | Any | 0/1 | Invalid
|
| 945 | *
|
| 946 | * [4] Found | Found | NULL | 0 | 1 | Valid
|
| 947 | * [5] Found | Found | NULL | >0 | 1 | Invalid
|
| 948 | *
|
| 949 | * [6] Found | Found | task | 0 | 1 | Valid
|
| 950 | *
|
| 951 | * [7] Found | Found | NULL | Any | 0 | Invalid
|
| 952 | *
|
| 953 | * [8] Found | Found | task | ==taskTID | 0/1 | Valid
|
| 954 | * [9] Found | Found | task | 0 | 0 | Invalid
|
| 955 | * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
|
| 956 | *
|
| 957 | * [1] Indicates that the kernel can acquire the futex atomically. We
|
| 958 | * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
|
| 959 | *
|
| 960 | * [2] Valid, if TID does not belong to a kernel thread. If no matching
|
| 961 | * thread is found then it indicates that the owner TID has died.
|
| 962 | *
|
| 963 | * [3] Invalid. The waiter is queued on a non PI futex
|
| 964 | *
|
| 965 | * [4] Valid state after exit_robust_list(), which sets the user space
|
| 966 | * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
|
| 967 | *
|
| 968 | * [5] The user space value got manipulated between exit_robust_list()
|
| 969 | * and exit_pi_state_list()
|
| 970 | *
|
| 971 | * [6] Valid state after exit_pi_state_list() which sets the new owner in
|
| 972 | * the pi_state but cannot access the user space value.
|
| 973 | *
|
| 974 | * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
|
| 975 | *
|
| 976 | * [8] Owner and user space value match
|
| 977 | *
|
| 978 | * [9] There is no transient state which sets the user space TID to 0
|
| 979 | * except exit_robust_list(), but this is indicated by the
|
| 980 | * FUTEX_OWNER_DIED bit. See [4]
|
| 981 | *
|
| 982 | * [10] There is no transient state which leaves owner and user space
|
| 983 | * TID out of sync.
|
| 984 | *
|
| 985 | *
|
| 986 | * Serialization and lifetime rules:
|
| 987 | *
|
| 988 | * hb->lock:
|
| 989 | *
|
| 990 | * hb -> futex_q, relation
|
| 991 | * futex_q -> pi_state, relation
|
| 992 | *
|
| 993 | * (cannot be raw because hb can contain arbitrary amount
|
| 994 | * of futex_q's)
|
| 995 | *
|
| 996 | * pi_mutex->wait_lock:
|
| 997 | *
|
| 998 | * {uval, pi_state}
|
| 999 | *
|
| 1000 | * (and pi_mutex 'obviously')
|
| 1001 | *
|
| 1002 | * p->pi_lock:
|
| 1003 | *
|
| 1004 | * p->pi_state_list -> pi_state->list, relation
|
| 1005 | *
|
| 1006 | * pi_state->refcount:
|
| 1007 | *
|
| 1008 | * pi_state lifetime
|
| 1009 | *
|
| 1010 | *
|
| 1011 | * Lock order:
|
| 1012 | *
|
| 1013 | * hb->lock
|
| 1014 | * pi_mutex->wait_lock
|
| 1015 | * p->pi_lock
|
| 1016 | *
|
| 1017 |
|
| 1018 |
|
| 1019 | |
| 1020 | * Validate that the existing waiter has a pi_state and sanity check
|
| 1021 | * the pi_state against the user space value. If correct, attach to
|
| 1022 | * it.
|
| 1023 |
|
| 1024 | static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
|
| 1025 | struct futex_pi_state *pi_state,
|
| 1026 | struct futex_pi_state **ps)
|
| 1027 | {
|
| 1028 | pid_t pid = uval & FUTEX_TID_MASK;
|
| 1029 | u32 uval2;
|
| 1030 | int ret;
|
| 1031 |
|
| 1032 | |
| 1033 | * Userspace might have messed up non-PI and PI futexes [3]
|
| 1034 |
|
| 1035 | if (unlikely(!pi_state))
|
| 1036 | return -EINVAL;
|
| 1037 |
|
| 1038 | |
| 1039 | * We get here with hb->lock held, and having found a
|
| 1040 | * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
|
| 1041 | * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
|
| 1042 | * which in turn means that futex_lock_pi() still has a reference on
|
| 1043 | * our pi_state.
|
| 1044 | *
|
| 1045 | * The waiter holding a reference on @pi_state also protects against
|
| 1046 | * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
|
| 1047 | * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
|
| 1048 | * free pi_state before we can take a reference ourselves.
|
| 1049 |
|
| 1050 | WARN_ON(!atomic_read(&pi_state->refcount));
|
| 1051 |
|
| 1052 | |
| 1053 | * Now that we have a pi_state, we can acquire wait_lock
|
| 1054 | * and do the state validation.
|
| 1055 |
|
| 1056 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
|
| 1057 |
|
| 1058 | |
| 1059 | * Since {uval, pi_state} is serialized by wait_lock, and our current
|
| 1060 | * uval was read without holding it, it can have changed. Verify it
|
| 1061 | * still is what we expect it to be, otherwise retry the entire
|
| 1062 | * operation.
|
| 1063 |
|
| 1064 | if (get_futex_value_locked(&uval2, uaddr))
|
| 1065 | goto out_efault;
|
| 1066 |
|
| 1067 | if (uval != uval2)
|
| 1068 | goto out_eagain;
|
| 1069 |
|
| 1070 | |
| 1071 | * Handle the owner died case:
|
| 1072 |
|
| 1073 | if (uval & FUTEX_OWNER_DIED) {
|
| 1074 | |
| 1075 | * exit_pi_state_list sets owner to NULL and wakes the
|
| 1076 | * topmost waiter. The task which acquires the
|
| 1077 | * pi_state->rt_mutex will fixup owner.
|
| 1078 |
|
| 1079 | if (!pi_state->owner) {
|
| 1080 | |
| 1081 | * No pi state owner, but the user space TID
|
| 1082 | * is not 0. Inconsistent state. [5]
|
| 1083 |
|
| 1084 | if (pid)
|
| 1085 | goto out_einval;
|
| 1086 | |
| 1087 | * Take a ref on the state and return success. [4]
|
| 1088 |
|
| 1089 | goto out_attach;
|
| 1090 | }
|
| 1091 |
|
| 1092 | |
| 1093 | * If TID is 0, then either the dying owner has not
|
| 1094 | * yet executed exit_pi_state_list() or some waiter
|
| 1095 | * acquired the rtmutex in the pi state, but did not
|
| 1096 | * yet fixup the TID in user space.
|
| 1097 | *
|
| 1098 | * Take a ref on the state and return success. [6]
|
| 1099 |
|
| 1100 | if (!pid)
|
| 1101 | goto out_attach;
|
| 1102 | } else {
|
| 1103 | |
| 1104 | * If the owner died bit is not set, then the pi_state
|
| 1105 | * must have an owner. [7]
|
| 1106 |
|
| 1107 | if (!pi_state->owner)
|
| 1108 | goto out_einval;
|
| 1109 | }
|
| 1110 |
|
| 1111 | |
| 1112 | * Bail out if user space manipulated the futex value. If pi
|
| 1113 | * state exists then the owner TID must be the same as the
|
| 1114 | * user space TID. [9/10]
|
| 1115 |
|
| 1116 | if (pid != task_pid_vnr(pi_state->owner))
|
| 1117 | goto out_einval;
|
| 1118 |
|
| 1119 | out_attach:
|
| 1120 | get_pi_state(pi_state);
|
| 1121 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
| 1122 | *ps = pi_state;
|
| 1123 | return 0;
|
| 1124 |
|
| 1125 | out_einval:
|
| 1126 | ret = -EINVAL;
|
| 1127 | goto out_error;
|
| 1128 |
|
| 1129 | out_eagain:
|
| 1130 | ret = -EAGAIN;
|
| 1131 | goto out_error;
|
| 1132 |
|
| 1133 | out_efault:
|
| 1134 | ret = -EFAULT;
|
| 1135 | goto out_error;
|
| 1136 |
|
| 1137 | out_error:
|
| 1138 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
| 1139 | return ret;
|
| 1140 | }
|
| 1141 |
|
| 1142 | |
| 1143 | * Lookup the task for the TID provided from user space and attach to
|
| 1144 | * it after doing proper sanity checks.
|
| 1145 |
|
| 1146 | static int attach_to_pi_owner(u32 uval, union futex_key *key,
|
| 1147 | struct futex_pi_state **ps)
|
| 1148 | {
|
| 1149 | pid_t pid = uval & FUTEX_TID_MASK;
|
| 1150 | struct futex_pi_state *pi_state;
|
| 1151 | struct task_struct *p;
|
| 1152 |
|
| 1153 | |
| 1154 | * We are the first waiter - try to look up the real owner and attach
|
| 1155 | * the new pi_state to it, but bail out when TID = 0 [1]
|
| 1156 |
|
| 1157 | if (!pid)
|
| 1158 | return -ESRCH;
|
| 1159 | p = futex_find_get_task(pid);
|
| 1160 | if (!p)
|
| 1161 | return -ESRCH;
|
| 1162 |
|
| 1163 | if (unlikely(p->flags & PF_KTHREAD)) {
|
| 1164 | put_task_struct(p);
|
| 1165 | return -EPERM;
|
| 1166 | }
|
| 1167 |
|
| 1168 | |
| 1169 | * We need to look at the task state flags to figure out,
|
| 1170 | * whether the task is exiting. To protect against the do_exit
|
| 1171 | * change of the task flags, we do this protected by
|
| 1172 | * p->pi_lock:
|
| 1173 |
|
| 1174 | raw_spin_lock_irq(&p->pi_lock);
|
| 1175 | if (unlikely(p->flags & PF_EXITING)) {
|
| 1176 | |
| 1177 | * The task is on the way out. When PF_EXITPIDONE is
|
| 1178 | * set, we know that the task has finished the
|
| 1179 | * cleanup:
|
| 1180 |
|
| 1181 | int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
|
| 1182 |
|
| 1183 | raw_spin_unlock_irq(&p->pi_lock);
|
| 1184 | put_task_struct(p);
|
| 1185 | return ret;
|
| 1186 | }
|
| 1187 |
|
| 1188 | |
| 1189 | * No existing pi state. First waiter. [2]
|
| 1190 | *
|
| 1191 | * This creates pi_state, we have hb->lock held, this means nothing can
|
| 1192 | * observe this state, wait_lock is irrelevant.
|
| 1193 |
|
| 1194 | pi_state = alloc_pi_state();
|
| 1195 |
|
| 1196 | |
| 1197 | * Initialize the pi_mutex in locked state and make @p
|
| 1198 | * the owner of it:
|
| 1199 |
|
| 1200 | rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
|
| 1201 |
|
| 1202 |
|
| 1203 | pi_state->key = *key;
|
| 1204 |
|
| 1205 | WARN_ON(!list_empty(&pi_state->list));
|
| 1206 | list_add(&pi_state->list, &p->pi_state_list);
|
| 1207 | pi_state->owner = p;
|
| 1208 | raw_spin_unlock_irq(&p->pi_lock);
|
| 1209 |
|
| 1210 | put_task_struct(p);
|
| 1211 |
|
| 1212 | *ps = pi_state;
|
| 1213 |
|
| 1214 | return 0;
|
| 1215 | }
|
| 1216 |
|
| 1217 | static int lookup_pi_state(u32 __user *uaddr, u32 uval,
|
| 1218 | struct futex_hash_bucket *hb,
|
| 1219 | union futex_key *key, struct futex_pi_state **ps)
|
| 1220 | {
|
| 1221 | struct futex_q *top_waiter = futex_top_waiter(hb, key);
|
| 1222 |
|
| 1223 | |
| 1224 | * If there is a waiter on that futex, validate it and
|
| 1225 | * attach to the pi_state when the validation succeeds.
|
| 1226 |
|
| 1227 | if (top_waiter)
|
| 1228 | return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
|
| 1229 |
|
| 1230 | |
| 1231 | * We are the first waiter - try to look up the owner based on
|
| 1232 | * @uval and attach to it.
|
| 1233 |
|
| 1234 | return attach_to_pi_owner(uval, key, ps);
|
| 1235 | }
|
| 1236 |
|
| 1237 | static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
|
| 1238 | {
|
| 1239 | u32 uninitialized_var(curval);
|
| 1240 |
|
| 1241 | if (unlikely(should_fail_futex(true)))
|
| 1242 | return -EFAULT;
|
| 1243 |
|
| 1244 | if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
|
| 1245 | return -EFAULT;
|
| 1246 |
|
| 1247 |
|
| 1248 | return curval != uval ? -EAGAIN : 0;
|
| 1249 | }
|
| 1250 |
|
| 1251 | |
| 1252 | * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
|
| 1253 | * @uaddr: the pi futex user address
|
| 1254 | * @hb: the pi futex hash bucket
|
| 1255 | * @key: the futex key associated with uaddr and hb
|
| 1256 | * @ps: the pi_state pointer where we store the result of the
|
| 1257 | * lookup
|
| 1258 | * @task: the task to perform the atomic lock work for. This will
|
| 1259 | * be "current" except in the case of requeue pi.
|
| 1260 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
|
| 1261 | *
|
| 1262 | * Return:
|
| 1263 | * - 0 - ready to wait;
|
| 1264 | * - 1 - acquired the lock;
|
| 1265 | * - <0 - error
|
| 1266 | *
|
| 1267 | * The hb->lock and futex_key refs shall be held by the caller.
|
| 1268 |
|
| 1269 | static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
|
| 1270 | union futex_key *key,
|
| 1271 | struct futex_pi_state **ps,
|
| 1272 | struct task_struct *task, int set_waiters)
|
| 1273 | {
|
| 1274 | u32 uval, newval, vpid = task_pid_vnr(task);
|
| 1275 | struct futex_q *top_waiter;
|
| 1276 | int ret;
|
| 1277 |
|
| 1278 | |
| 1279 | * Read the user space value first so we can validate a few
|
| 1280 | * things before proceeding further.
|
| 1281 |
|
| 1282 | if (get_futex_value_locked(&uval, uaddr))
|
| 1283 | return -EFAULT;
|
| 1284 |
|
| 1285 | if (unlikely(should_fail_futex(true)))
|
| 1286 | return -EFAULT;
|
| 1287 |
|
| 1288 | |
| 1289 | * Detect deadlocks.
|
| 1290 |
|
| 1291 | if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
|
| 1292 | return -EDEADLK;
|
| 1293 |
|
| 1294 | if ((unlikely(should_fail_futex(true))))
|
| 1295 | return -EDEADLK;
|
| 1296 |
|
| 1297 | |
| 1298 | * Lookup existing state first. If it exists, try to attach to
|
| 1299 | * its pi_state.
|
| 1300 |
|
| 1301 | top_waiter = futex_top_waiter(hb, key);
|
| 1302 | if (top_waiter)
|
| 1303 | return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
|
| 1304 |
|
| 1305 | |
| 1306 | * No waiter and user TID is 0. We are here because the
|
| 1307 | * waiters or the owner died bit is set or called from
|
| 1308 | * requeue_cmp_pi or for whatever reason something took the
|
| 1309 | * syscall.
|
| 1310 |
|
| 1311 | if (!(uval & FUTEX_TID_MASK)) {
|
| 1312 | |
| 1313 | * We take over the futex. No other waiters and the user space
|
| 1314 | * TID is 0. We preserve the owner died bit.
|
| 1315 |
|
| 1316 | newval = uval & FUTEX_OWNER_DIED;
|
| 1317 | newval |= vpid;
|
| 1318 |
|
| 1319 |
|
| 1320 | if (set_waiters)
|
| 1321 | newval |= FUTEX_WAITERS;
|
| 1322 |
|
| 1323 | ret = lock_pi_update_atomic(uaddr, uval, newval);
|
| 1324 |
|
| 1325 | return ret < 0 ? ret : 1;
|
| 1326 | }
|
| 1327 |
|
| 1328 | |
| 1329 | * First waiter. Set the waiters bit before attaching ourself to
|
| 1330 | * the owner. If owner tries to unlock, it will be forced into
|
| 1331 | * the kernel and blocked on hb->lock.
|
| 1332 |
|
| 1333 | newval = uval | FUTEX_WAITERS;
|
| 1334 | ret = lock_pi_update_atomic(uaddr, uval, newval);
|
| 1335 | if (ret)
|
| 1336 | return ret;
|
| 1337 | |
| 1338 | * If the update of the user space value succeeded, we try to
|
| 1339 | * attach to the owner. If that fails, no harm done, we only
|
| 1340 | * set the FUTEX_WAITERS bit in the user space variable.
|
| 1341 |
|
| 1342 | return attach_to_pi_owner(uval, key, ps);
|
| 1343 | }
|
| 1344 |
|
| 1345 | |
| 1346 | * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
|
| 1347 | * @q: The futex_q to unqueue
|
| 1348 | *
|
| 1349 | * The q->lock_ptr must not be NULL and must be held by the caller.
|
| 1350 |
|
| 1351 | static void __unqueue_futex(struct futex_q *q)
|
| 1352 | {
|
| 1353 | struct futex_hash_bucket *hb;
|
| 1354 |
|
| 1355 | if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
|
| 1356 | || WARN_ON(plist_node_empty(&q->list)))
|
| 1357 | return;
|
| 1358 |
|
| 1359 | hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
|
| 1360 | plist_del(&q->list, &hb->chain);
|
| 1361 | hb_waiters_dec(hb);
|
| 1362 | }
|
| 1363 |
|
| 1364 | |
| 1365 | * The hash bucket lock must be held when this is called.
|
| 1366 | * Afterwards, the futex_q must not be accessed. Callers
|
| 1367 | * must ensure to later call wake_up_q() for the actual
|
| 1368 | * wakeups to occur.
|
| 1369 |
|
| 1370 | static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
|
| 1371 | {
|
| 1372 | struct task_struct *p = q->task;
|
| 1373 |
|
| 1374 | if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
|
| 1375 | return;
|
| 1376 |
|
| 1377 | |
| 1378 | * Queue the task for later wakeup for after we've released
|
| 1379 | * the hb->lock. wake_q_add() grabs reference to p.
|
| 1380 |
|
| 1381 | wake_q_add(wake_q, p);
|
| 1382 | __unqueue_futex(q);
|
| 1383 | |
| 1384 | * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
|
| 1385 | * is written, without taking any locks. This is possible in the event
|
| 1386 | * of a spurious wakeup, for example. A memory barrier is required here
|
| 1387 | * to prevent the following store to lock_ptr from getting ahead of the
|
| 1388 | * plist_del in __unqueue_futex().
|
| 1389 |
|
| 1390 | smp_store_release(&q->lock_ptr, NULL);
|
| 1391 | }
|
| 1392 |
|
| 1393 | |
| 1394 | * Caller must hold a reference on @pi_state.
|
| 1395 |
|
| 1396 | static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
|
| 1397 | {
|
| 1398 | u32 uninitialized_var(curval), newval;
|
| 1399 | struct task_struct *new_owner;
|
| 1400 | bool postunlock = false;
|
| 1401 | DEFINE_WAKE_Q(wake_q);
|
| 1402 | int ret = 0;
|
| 1403 |
|
| 1404 | new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
|
| 1405 | if (WARN_ON_ONCE(!new_owner)) {
|
| 1406 | |
| 1407 | * As per the comment in futex_unlock_pi() this should not happen.
|
| 1408 | *
|
| 1409 | * When this happens, give up our locks and try again, giving
|
| 1410 | * the futex_lock_pi() instance time to complete, either by
|
| 1411 | * waiting on the rtmutex or removing itself from the futex
|
| 1412 | * queue.
|
| 1413 |
|
| 1414 | ret = -EAGAIN;
|
| 1415 | goto out_unlock;
|
| 1416 | }
|
| 1417 |
|
| 1418 | |
| 1419 | * We pass it to the next owner. The WAITERS bit is always kept
|
| 1420 | * enabled while there is PI state around. We cleanup the owner
|
| 1421 | * died bit, because we are the owner.
|
| 1422 |
|
| 1423 | newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
|
| 1424 |
|
| 1425 | if (unlikely(should_fail_futex(true)))
|
| 1426 | ret = -EFAULT;
|
| 1427 |
|
| 1428 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) {
|
| 1429 | ret = -EFAULT;
|
| 1430 |
|
| 1431 | } else if (curval != uval) {
|
| 1432 | |
| 1433 | * If a unconditional UNLOCK_PI operation (user space did not
|
| 1434 | * try the TID->0 transition) raced with a waiter setting the
|
| 1435 | * FUTEX_WAITERS flag between get_user() and locking the hash
|
| 1436 | * bucket lock, retry the operation.
|
| 1437 |
|
| 1438 | if ((FUTEX_TID_MASK & curval) == uval)
|
| 1439 | ret = -EAGAIN;
|
| 1440 | else
|
| 1441 | ret = -EINVAL;
|
| 1442 | }
|
| 1443 |
|
| 1444 | if (ret)
|
| 1445 | goto out_unlock;
|
| 1446 |
|
| 1447 | |
| 1448 | * This is a point of no return; once we modify the uval there is no
|
| 1449 | * going back and subsequent operations must not fail.
|
| 1450 |
|
| 1451 |
|
| 1452 | raw_spin_lock(&pi_state->owner->pi_lock);
|
| 1453 | WARN_ON(list_empty(&pi_state->list));
|
| 1454 | list_del_init(&pi_state->list);
|
| 1455 | raw_spin_unlock(&pi_state->owner->pi_lock);
|
| 1456 |
|
| 1457 | raw_spin_lock(&new_owner->pi_lock);
|
| 1458 | WARN_ON(!list_empty(&pi_state->list));
|
| 1459 | list_add(&pi_state->list, &new_owner->pi_state_list);
|
| 1460 | pi_state->owner = new_owner;
|
| 1461 | raw_spin_unlock(&new_owner->pi_lock);
|
| 1462 |
|
| 1463 | postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
|
| 1464 |
|
| 1465 | out_unlock:
|
| 1466 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
| 1467 |
|
| 1468 | if (postunlock)
|
| 1469 | rt_mutex_postunlock(&wake_q);
|
| 1470 |
|
| 1471 | return ret;
|
| 1472 | }
|
| 1473 |
|
| 1474 | |
| 1475 | * Express the locking dependencies for lockdep:
|
| 1476 |
|
| 1477 | static inline void
|
| 1478 | double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
|
| 1479 | {
|
| 1480 | if (hb1 <= hb2) {
|
| 1481 | spin_lock(&hb1->lock);
|
| 1482 | if (hb1 < hb2)
|
| 1483 | spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
|
| 1484 | } else {
|
| 1485 | spin_lock(&hb2->lock);
|
| 1486 | spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
|
| 1487 | }
|
| 1488 | }
|
| 1489 |
|
| 1490 | static inline void
|
| 1491 | double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
|
| 1492 | {
|
| 1493 | spin_unlock(&hb1->lock);
|
| 1494 | if (hb1 != hb2)
|
| 1495 | spin_unlock(&hb2->lock);
|
| 1496 | }
|
| 1497 |
|
| 1498 | |
| 1499 | * Wake up waiters matching bitset queued on this futex (uaddr).
|
| 1500 |
|
| 1501 | static int
|
| 1502 | futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
|
| 1503 | {
|
| 1504 | struct futex_hash_bucket *hb;
|
| 1505 | struct futex_q *this, *next;
|
| 1506 | union futex_key key = FUTEX_KEY_INIT;
|
| 1507 | int ret;
|
| 1508 | DEFINE_WAKE_Q(wake_q);
|
| 1509 |
|
| 1510 | if (!bitset)
|
| 1511 | return -EINVAL;
|
| 1512 |
|
| 1513 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
|
| 1514 | if (unlikely(ret != 0))
|
| 1515 | goto out;
|
| 1516 |
|
| 1517 | hb = hash_futex(&key);
|
| 1518 |
|
| 1519 |
|
| 1520 | if (!hb_waiters_pending(hb))
|
| 1521 | goto out_put_key;
|
| 1522 |
|
| 1523 | spin_lock(&hb->lock);
|
| 1524 |
|
| 1525 | plist_for_each_entry_safe(this, next, &hb->chain, list) {
|
| 1526 | if (match_futex (&this->key, &key)) {
|
| 1527 | if (this->pi_state || this->rt_waiter) {
|
| 1528 | ret = -EINVAL;
|
| 1529 | break;
|
| 1530 | }
|
| 1531 |
|
| 1532 |
|
| 1533 | if (!(this->bitset & bitset))
|
| 1534 | continue;
|
| 1535 |
|
| 1536 | mark_wake_futex(&wake_q, this);
|
| 1537 | if (++ret >= nr_wake)
|
| 1538 | break;
|
| 1539 | }
|
| 1540 | }
|
| 1541 |
|
| 1542 | spin_unlock(&hb->lock);
|
| 1543 | wake_up_q(&wake_q);
|
| 1544 | out_put_key:
|
| 1545 | put_futex_key(&key);
|
| 1546 | out:
|
| 1547 | return ret;
|
| 1548 | }
|
| 1549 |
|
| 1550 | |
| 1551 | * Wake up all waiters hashed on the physical page that is mapped
|
| 1552 | * to this virtual address:
|
| 1553 |
|
| 1554 | static int
|
| 1555 | futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
|
| 1556 | int nr_wake, int nr_wake2, int op)
|
| 1557 | {
|
| 1558 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
|
| 1559 | struct futex_hash_bucket *hb1, *hb2;
|
| 1560 | struct futex_q *this, *next;
|
| 1561 | int ret, op_ret;
|
| 1562 | DEFINE_WAKE_Q(wake_q);
|
| 1563 |
|
| 1564 | retry:
|
| 1565 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
|
| 1566 | if (unlikely(ret != 0))
|
| 1567 | goto out;
|
| 1568 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
|
| 1569 | if (unlikely(ret != 0))
|
| 1570 | goto out_put_key1;
|
| 1571 |
|
| 1572 | hb1 = hash_futex(&key1);
|
| 1573 | hb2 = hash_futex(&key2);
|
| 1574 |
|
| 1575 | retry_private:
|
| 1576 | double_lock_hb(hb1, hb2);
|
| 1577 | op_ret = futex_atomic_op_inuser(op, uaddr2);
|
| 1578 | if (unlikely(op_ret < 0)) {
|
| 1579 |
|
| 1580 | double_unlock_hb(hb1, hb2);
|
| 1581 |
|
| 1582 | #ifndef CONFIG_MMU
|
| 1583 | |
| 1584 | * we don't get EFAULT from MMU faults if we don't have an MMU,
|
| 1585 | * but we might get them from range checking
|
| 1586 |
|
| 1587 | ret = op_ret;
|
| 1588 | goto out_put_keys;
|
| 1589 | #endif
|
| 1590 |
|
| 1591 | if (unlikely(op_ret != -EFAULT)) {
|
| 1592 | ret = op_ret;
|
| 1593 | goto out_put_keys;
|
| 1594 | }
|
| 1595 |
|
| 1596 | ret = fault_in_user_writeable(uaddr2);
|
| 1597 | if (ret)
|
| 1598 | goto out_put_keys;
|
| 1599 |
|
| 1600 | if (!(flags & FLAGS_SHARED))
|
| 1601 | goto retry_private;
|
| 1602 |
|
| 1603 | put_futex_key(&key2);
|
| 1604 | put_futex_key(&key1);
|
| 1605 | goto retry;
|
| 1606 | }
|
| 1607 |
|
| 1608 | plist_for_each_entry_safe(this, next, &hb1->chain, list) {
|
| 1609 | if (match_futex (&this->key, &key1)) {
|
| 1610 | if (this->pi_state || this->rt_waiter) {
|
| 1611 | ret = -EINVAL;
|
| 1612 | goto out_unlock;
|
| 1613 | }
|
| 1614 | mark_wake_futex(&wake_q, this);
|
| 1615 | if (++ret >= nr_wake)
|
| 1616 | break;
|
| 1617 | }
|
| 1618 | }
|
| 1619 |
|
| 1620 | if (op_ret > 0) {
|
| 1621 | op_ret = 0;
|
| 1622 | plist_for_each_entry_safe(this, next, &hb2->chain, list) {
|
| 1623 | if (match_futex (&this->key, &key2)) {
|
| 1624 | if (this->pi_state || this->rt_waiter) {
|
| 1625 | ret = -EINVAL;
|
| 1626 | goto out_unlock;
|
| 1627 | }
|
| 1628 | mark_wake_futex(&wake_q, this);
|
| 1629 | if (++op_ret >= nr_wake2)
|
| 1630 | break;
|
| 1631 | }
|
| 1632 | }
|
| 1633 | ret += op_ret;
|
| 1634 | }
|
| 1635 |
|
| 1636 | out_unlock:
|
| 1637 | double_unlock_hb(hb1, hb2);
|
| 1638 | wake_up_q(&wake_q);
|
| 1639 | out_put_keys:
|
| 1640 | put_futex_key(&key2);
|
| 1641 | out_put_key1:
|
| 1642 | put_futex_key(&key1);
|
| 1643 | out:
|
| 1644 | return ret;
|
| 1645 | }
|
| 1646 |
|
| 1647 | |
| 1648 | * requeue_futex() - Requeue a futex_q from one hb to another
|
| 1649 | * @q: the futex_q to requeue
|
| 1650 | * @hb1: the source hash_bucket
|
| 1651 | * @hb2: the target hash_bucket
|
| 1652 | * @key2: the new key for the requeued futex_q
|
| 1653 |
|
| 1654 | static inline
|
| 1655 | void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
|
| 1656 | struct futex_hash_bucket *hb2, union futex_key *key2)
|
| 1657 | {
|
| 1658 |
|
| 1659 | |
| 1660 | * If key1 and key2 hash to the same bucket, no need to
|
| 1661 | * requeue.
|
| 1662 |
|
| 1663 | if (likely(&hb1->chain != &hb2->chain)) {
|
| 1664 | plist_del(&q->list, &hb1->chain);
|
| 1665 | hb_waiters_dec(hb1);
|
| 1666 | hb_waiters_inc(hb2);
|
| 1667 | plist_add(&q->list, &hb2->chain);
|
| 1668 | q->lock_ptr = &hb2->lock;
|
| 1669 | }
|
| 1670 | get_futex_key_refs(key2);
|
| 1671 | q->key = *key2;
|
| 1672 | }
|
| 1673 |
|
| 1674 | |
| 1675 | * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
|
| 1676 | * @q: the futex_q
|
| 1677 | * @key: the key of the requeue target futex
|
| 1678 | * @hb: the hash_bucket of the requeue target futex
|
| 1679 | *
|
| 1680 | * During futex_requeue, with requeue_pi=1, it is possible to acquire the
|
| 1681 | * target futex if it is uncontended or via a lock steal. Set the futex_q key
|
| 1682 | * to the requeue target futex so the waiter can detect the wakeup on the right
|
| 1683 | * futex, but remove it from the hb and NULL the rt_waiter so it can detect
|
| 1684 | * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
|
| 1685 | * to protect access to the pi_state to fixup the owner later. Must be called
|
| 1686 | * with both q->lock_ptr and hb->lock held.
|
| 1687 |
|
| 1688 | static inline
|
| 1689 | void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
|
| 1690 | struct futex_hash_bucket *hb)
|
| 1691 | {
|
| 1692 | get_futex_key_refs(key);
|
| 1693 | q->key = *key;
|
| 1694 |
|
| 1695 | __unqueue_futex(q);
|
| 1696 |
|
| 1697 | WARN_ON(!q->rt_waiter);
|
| 1698 | q->rt_waiter = NULL;
|
| 1699 |
|
| 1700 | q->lock_ptr = &hb->lock;
|
| 1701 |
|
| 1702 | wake_up_state(q->task, TASK_NORMAL);
|
| 1703 | }
|
| 1704 |
|
| 1705 | |
| 1706 | * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
|
| 1707 | * @pifutex: the user address of the to futex
|
| 1708 | * @hb1: the from futex hash bucket, must be locked by the caller
|
| 1709 | * @hb2: the to futex hash bucket, must be locked by the caller
|
| 1710 | * @key1: the from futex key
|
| 1711 | * @key2: the to futex key
|
| 1712 | * @ps: address to store the pi_state pointer
|
| 1713 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
|
| 1714 | *
|
| 1715 | * Try and get the lock on behalf of the top waiter if we can do it atomically.
|
| 1716 | * Wake the top waiter if we succeed. If the caller specified set_waiters,
|
| 1717 | * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
|
| 1718 | * hb1 and hb2 must be held by the caller.
|
| 1719 | *
|
| 1720 | * Return:
|
| 1721 | * - 0 - failed to acquire the lock atomically;
|
| 1722 | * - >0 - acquired the lock, return value is vpid of the top_waiter
|
| 1723 | * - <0 - error
|
| 1724 |
|
| 1725 | static int futex_proxy_trylock_atomic(u32 __user *pifutex,
|
| 1726 | struct futex_hash_bucket *hb1,
|
| 1727 | struct futex_hash_bucket *hb2,
|
| 1728 | union futex_key *key1, union futex_key *key2,
|
| 1729 | struct futex_pi_state **ps, int set_waiters)
|
| 1730 | {
|
| 1731 | struct futex_q *top_waiter = NULL;
|
| 1732 | u32 curval;
|
| 1733 | int ret, vpid;
|
| 1734 |
|
| 1735 | if (get_futex_value_locked(&curval, pifutex))
|
| 1736 | return -EFAULT;
|
| 1737 |
|
| 1738 | if (unlikely(should_fail_futex(true)))
|
| 1739 | return -EFAULT;
|
| 1740 |
|
| 1741 | |
| 1742 | * Find the top_waiter and determine if there are additional waiters.
|
| 1743 | * If the caller intends to requeue more than 1 waiter to pifutex,
|
| 1744 | * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
|
| 1745 | * as we have means to handle the possible fault. If not, don't set
|
| 1746 | * the bit unecessarily as it will force the subsequent unlock to enter
|
| 1747 | * the kernel.
|
| 1748 |
|
| 1749 | top_waiter = futex_top_waiter(hb1, key1);
|
| 1750 |
|
| 1751 |
|
| 1752 | if (!top_waiter)
|
| 1753 | return 0;
|
| 1754 |
|
| 1755 |
|
| 1756 | if (!match_futex(top_waiter->requeue_pi_key, key2))
|
| 1757 | return -EINVAL;
|
| 1758 |
|
| 1759 | |
| 1760 | * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
|
| 1761 | * the contended case or if set_waiters is 1. The pi_state is returned
|
| 1762 | * in ps in contended cases.
|
| 1763 |
|
| 1764 | vpid = task_pid_vnr(top_waiter->task);
|
| 1765 | ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
|
| 1766 | set_waiters);
|
| 1767 | if (ret == 1) {
|
| 1768 | requeue_pi_wake_futex(top_waiter, key2, hb2);
|
| 1769 | return vpid;
|
| 1770 | }
|
| 1771 | return ret;
|
| 1772 | }
|
| 1773 |
|
| 1774 | |
| 1775 | * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
|
| 1776 | * @uaddr1: source futex user address
|
| 1777 | * @flags: futex flags (FLAGS_SHARED, etc.)
|
| 1778 | * @uaddr2: target futex user address
|
| 1779 | * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
|
| 1780 | * @nr_requeue: number of waiters to requeue (0-INT_MAX)
|
| 1781 | * @cmpval: @uaddr1 expected value (or %NULL)
|
| 1782 | * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
|
| 1783 | * pi futex (pi to pi requeue is not supported)
|
| 1784 | *
|
| 1785 | * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
|
| 1786 | * uaddr2 atomically on behalf of the top waiter.
|
| 1787 | *
|
| 1788 | * Return:
|
| 1789 | * - >=0 - on success, the number of tasks requeued or woken;
|
| 1790 | * - <0 - on error
|
| 1791 |
|
| 1792 | static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
|
| 1793 | u32 __user *uaddr2, int nr_wake, int nr_requeue,
|
| 1794 | u32 *cmpval, int requeue_pi)
|
| 1795 | {
|
| 1796 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
|
| 1797 | int drop_count = 0, task_count = 0, ret;
|
| 1798 | struct futex_pi_state *pi_state = NULL;
|
| 1799 | struct futex_hash_bucket *hb1, *hb2;
|
| 1800 | struct futex_q *this, *next;
|
| 1801 | DEFINE_WAKE_Q(wake_q);
|
| 1802 |
|
| 1803 | if (requeue_pi) {
|
| 1804 | |
| 1805 | * Requeue PI only works on two distinct uaddrs. This
|
| 1806 | * check is only valid for private futexes. See below.
|
| 1807 |
|
| 1808 | if (uaddr1 == uaddr2)
|
| 1809 | return -EINVAL;
|
| 1810 |
|
| 1811 | |
| 1812 | * requeue_pi requires a pi_state, try to allocate it now
|
| 1813 | * without any locks in case it fails.
|
| 1814 |
|
| 1815 | if (refill_pi_state_cache())
|
| 1816 | return -ENOMEM;
|
| 1817 | |
| 1818 | * requeue_pi must wake as many tasks as it can, up to nr_wake
|
| 1819 | * + nr_requeue, since it acquires the rt_mutex prior to
|
| 1820 | * returning to userspace, so as to not leave the rt_mutex with
|
| 1821 | * waiters and no owner. However, second and third wake-ups
|
| 1822 | * cannot be predicted as they involve race conditions with the
|
| 1823 | * first wake and a fault while looking up the pi_state. Both
|
| 1824 | * pthread_cond_signal() and pthread_cond_broadcast() should
|
| 1825 | * use nr_wake=1.
|
| 1826 |
|
| 1827 | if (nr_wake != 1)
|
| 1828 | return -EINVAL;
|
| 1829 | }
|
| 1830 |
|
| 1831 | retry:
|
| 1832 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
|
| 1833 | if (unlikely(ret != 0))
|
| 1834 | goto out;
|
| 1835 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
|
| 1836 | requeue_pi ? VERIFY_WRITE : VERIFY_READ);
|
| 1837 | if (unlikely(ret != 0))
|
| 1838 | goto out_put_key1;
|
| 1839 |
|
| 1840 | |
| 1841 | * The check above which compares uaddrs is not sufficient for
|
| 1842 | * shared futexes. We need to compare the keys:
|
| 1843 |
|
| 1844 | if (requeue_pi && match_futex(&key1, &key2)) {
|
| 1845 | ret = -EINVAL;
|
| 1846 | goto out_put_keys;
|
| 1847 | }
|
| 1848 |
|
| 1849 | hb1 = hash_futex(&key1);
|
| 1850 | hb2 = hash_futex(&key2);
|
| 1851 |
|
| 1852 | retry_private:
|
| 1853 | hb_waiters_inc(hb2);
|
| 1854 | double_lock_hb(hb1, hb2);
|
| 1855 |
|
| 1856 | if (likely(cmpval != NULL)) {
|
| 1857 | u32 curval;
|
| 1858 |
|
| 1859 | ret = get_futex_value_locked(&curval, uaddr1);
|
| 1860 |
|
| 1861 | if (unlikely(ret)) {
|
| 1862 | double_unlock_hb(hb1, hb2);
|
| 1863 | hb_waiters_dec(hb2);
|
| 1864 |
|
| 1865 | ret = get_user(curval, uaddr1);
|
| 1866 | if (ret)
|
| 1867 | goto out_put_keys;
|
| 1868 |
|
| 1869 | if (!(flags & FLAGS_SHARED))
|
| 1870 | goto retry_private;
|
| 1871 |
|
| 1872 | put_futex_key(&key2);
|
| 1873 | put_futex_key(&key1);
|
| 1874 | goto retry;
|
| 1875 | }
|
| 1876 | if (curval != *cmpval) {
|
| 1877 | ret = -EAGAIN;
|
| 1878 | goto out_unlock;
|
| 1879 | }
|
| 1880 | }
|
| 1881 |
|
| 1882 | if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
|
| 1883 | |
| 1884 | * Attempt to acquire uaddr2 and wake the top waiter. If we
|
| 1885 | * intend to requeue waiters, force setting the FUTEX_WAITERS
|
| 1886 | * bit. We force this here where we are able to easily handle
|
| 1887 | * faults rather in the requeue loop below.
|
| 1888 |
|
| 1889 | ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
|
| 1890 | &key2, &pi_state, nr_requeue);
|
| 1891 |
|
| 1892 | |
| 1893 | * At this point the top_waiter has either taken uaddr2 or is
|
| 1894 | * waiting on it. If the former, then the pi_state will not
|
| 1895 | * exist yet, look it up one more time to ensure we have a
|
| 1896 | * reference to it. If the lock was taken, ret contains the
|
| 1897 | * vpid of the top waiter task.
|
| 1898 | * If the lock was not taken, we have pi_state and an initial
|
| 1899 | * refcount on it. In case of an error we have nothing.
|
| 1900 |
|
| 1901 | if (ret > 0) {
|
| 1902 | WARN_ON(pi_state);
|
| 1903 | drop_count++;
|
| 1904 | task_count++;
|
| 1905 | |
| 1906 | * If we acquired the lock, then the user space value
|
| 1907 | * of uaddr2 should be vpid. It cannot be changed by
|
| 1908 | * the top waiter as it is blocked on hb2 lock if it
|
| 1909 | * tries to do so. If something fiddled with it behind
|
| 1910 | * our back the pi state lookup might unearth it. So
|
| 1911 | * we rather use the known value than rereading and
|
| 1912 | * handing potential crap to lookup_pi_state.
|
| 1913 | *
|
| 1914 | * If that call succeeds then we have pi_state and an
|
| 1915 | * initial refcount on it.
|
| 1916 |
|
| 1917 | ret = lookup_pi_state(uaddr2, ret, hb2, &key2, &pi_state);
|
| 1918 | }
|
| 1919 |
|
| 1920 | switch (ret) {
|
| 1921 | case 0:
|
| 1922 |
|
| 1923 | break;
|
| 1924 |
|
| 1925 |
|
| 1926 | case -EFAULT:
|
| 1927 | double_unlock_hb(hb1, hb2);
|
| 1928 | hb_waiters_dec(hb2);
|
| 1929 | put_futex_key(&key2);
|
| 1930 | put_futex_key(&key1);
|
| 1931 | ret = fault_in_user_writeable(uaddr2);
|
| 1932 | if (!ret)
|
| 1933 | goto retry;
|
| 1934 | goto out;
|
| 1935 | case -EAGAIN:
|
| 1936 | |
| 1937 | * Two reasons for this:
|
| 1938 | * - Owner is exiting and we just wait for the
|
| 1939 | * exit to complete.
|
| 1940 | * - The user space value changed.
|
| 1941 |
|
| 1942 | double_unlock_hb(hb1, hb2);
|
| 1943 | hb_waiters_dec(hb2);
|
| 1944 | put_futex_key(&key2);
|
| 1945 | put_futex_key(&key1);
|
| 1946 | cond_resched();
|
| 1947 | goto retry;
|
| 1948 | default:
|
| 1949 | goto out_unlock;
|
| 1950 | }
|
| 1951 | }
|
| 1952 |
|
| 1953 | plist_for_each_entry_safe(this, next, &hb1->chain, list) {
|
| 1954 | if (task_count - nr_wake >= nr_requeue)
|
| 1955 | break;
|
| 1956 |
|
| 1957 | if (!match_futex(&this->key, &key1))
|
| 1958 | continue;
|
| 1959 |
|
| 1960 | |
| 1961 | * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
|
| 1962 | * be paired with each other and no other futex ops.
|
| 1963 | *
|
| 1964 | * We should never be requeueing a futex_q with a pi_state,
|
| 1965 | * which is awaiting a futex_unlock_pi().
|
| 1966 |
|
| 1967 | if ((requeue_pi && !this->rt_waiter) ||
|
| 1968 | (!requeue_pi && this->rt_waiter) ||
|
| 1969 | this->pi_state) {
|
| 1970 | ret = -EINVAL;
|
| 1971 | break;
|
| 1972 | }
|
| 1973 |
|
| 1974 | |
| 1975 | * Wake nr_wake waiters. For requeue_pi, if we acquired the
|
| 1976 | * lock, we already woke the top_waiter. If not, it will be
|
| 1977 | * woken by futex_unlock_pi().
|
| 1978 |
|
| 1979 | if (++task_count <= nr_wake && !requeue_pi) {
|
| 1980 | mark_wake_futex(&wake_q, this);
|
| 1981 | continue;
|
| 1982 | }
|
| 1983 |
|
| 1984 |
|
| 1985 | if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
|
| 1986 | ret = -EINVAL;
|
| 1987 | break;
|
| 1988 | }
|
| 1989 |
|
| 1990 | |
| 1991 | * Requeue nr_requeue waiters and possibly one more in the case
|
| 1992 | * of requeue_pi if we couldn't acquire the lock atomically.
|
| 1993 |
|
| 1994 | if (requeue_pi) {
|
| 1995 | |
| 1996 | * Prepare the waiter to take the rt_mutex. Take a
|
| 1997 | * refcount on the pi_state and store the pointer in
|
| 1998 | * the futex_q object of the waiter.
|
| 1999 |
|
| 2000 | get_pi_state(pi_state);
|
| 2001 | this->pi_state = pi_state;
|
| 2002 | ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
|
| 2003 | this->rt_waiter,
|
| 2004 | this->task);
|
| 2005 | if (ret == 1) {
|
| 2006 | |
| 2007 | * We got the lock. We do neither drop the
|
| 2008 | * refcount on pi_state nor clear
|
| 2009 | * this->pi_state because the waiter needs the
|
| 2010 | * pi_state for cleaning up the user space
|
| 2011 | * value. It will drop the refcount after
|
| 2012 | * doing so.
|
| 2013 |
|
| 2014 | requeue_pi_wake_futex(this, &key2, hb2);
|
| 2015 | drop_count++;
|
| 2016 | continue;
|
| 2017 | } else if (ret) {
|
| 2018 | |
| 2019 | * rt_mutex_start_proxy_lock() detected a
|
| 2020 | * potential deadlock when we tried to queue
|
| 2021 | * that waiter. Drop the pi_state reference
|
| 2022 | * which we took above and remove the pointer
|
| 2023 | * to the state from the waiters futex_q
|
| 2024 | * object.
|
| 2025 |
|
| 2026 | this->pi_state = NULL;
|
| 2027 | put_pi_state(pi_state);
|
| 2028 | |
| 2029 | * We stop queueing more waiters and let user
|
| 2030 | * space deal with the mess.
|
| 2031 |
|
| 2032 | break;
|
| 2033 | }
|
| 2034 | }
|
| 2035 | requeue_futex(this, hb1, hb2, &key2);
|
| 2036 | drop_count++;
|
| 2037 | }
|
| 2038 |
|
| 2039 | |
| 2040 | * We took an extra initial reference to the pi_state either
|
| 2041 | * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We
|
| 2042 | * need to drop it here again.
|
| 2043 |
|
| 2044 | put_pi_state(pi_state);
|
| 2045 |
|
| 2046 | out_unlock:
|
| 2047 | double_unlock_hb(hb1, hb2);
|
| 2048 | wake_up_q(&wake_q);
|
| 2049 | hb_waiters_dec(hb2);
|
| 2050 |
|
| 2051 | |
| 2052 | * drop_futex_key_refs() must be called outside the spinlocks. During
|
| 2053 | * the requeue we moved futex_q's from the hash bucket at key1 to the
|
| 2054 | * one at key2 and updated their key pointer. We no longer need to
|
| 2055 | * hold the references to key1.
|
| 2056 |
|
| 2057 | while (--drop_count >= 0)
|
| 2058 | drop_futex_key_refs(&key1);
|
| 2059 |
|
| 2060 | out_put_keys:
|
| 2061 | put_futex_key(&key2);
|
| 2062 | out_put_key1:
|
| 2063 | put_futex_key(&key1);
|
| 2064 | out:
|
| 2065 | return ret ? ret : task_count;
|
| 2066 | }
|
| 2067 |
|
| 2068 |
|
| 2069 | static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
|
| 2070 | __acquires(&hb->lock)
|
| 2071 | {
|
| 2072 | struct futex_hash_bucket *hb;
|
| 2073 |
|
| 2074 | hb = hash_futex(&q->key);
|
| 2075 |
|
| 2076 | |
| 2077 | * Increment the counter before taking the lock so that
|
| 2078 | * a potential waker won't miss a to-be-slept task that is
|
| 2079 | * waiting for the spinlock. This is safe as all queue_lock()
|
| 2080 | * users end up calling queue_me(). Similarly, for housekeeping,
|
| 2081 | * decrement the counter at queue_unlock() when some error has
|
| 2082 | * occurred and we don't end up adding the task to the list.
|
| 2083 |
|
| 2084 | hb_waiters_inc(hb);
|
| 2085 |
|
| 2086 | q->lock_ptr = &hb->lock;
|
| 2087 |
|
| 2088 | spin_lock(&hb->lock);
|
| 2089 | return hb;
|
| 2090 | }
|
| 2091 |
|
| 2092 | static inline void
|
| 2093 | queue_unlock(struct futex_hash_bucket *hb)
|
| 2094 | __releases(&hb->lock)
|
| 2095 | {
|
| 2096 | spin_unlock(&hb->lock);
|
| 2097 | hb_waiters_dec(hb);
|
| 2098 | }
|
| 2099 |
|
| 2100 | static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
|
| 2101 | {
|
| 2102 | int prio;
|
| 2103 |
|
| 2104 | |
| 2105 | * The priority used to register this element is
|
| 2106 | * - either the real thread-priority for the real-time threads
|
| 2107 | * (i.e. threads with a priority lower than MAX_RT_PRIO)
|
| 2108 | * - or MAX_RT_PRIO for non-RT threads.
|
| 2109 | * Thus, all RT-threads are woken first in priority order, and
|
| 2110 | * the others are woken last, in FIFO order.
|
| 2111 |
|
| 2112 | prio = min(current->normal_prio, MAX_RT_PRIO);
|
| 2113 |
|
| 2114 | plist_node_init(&q->list, prio);
|
| 2115 | plist_add(&q->list, &hb->chain);
|
| 2116 | q->task = current;
|
| 2117 | }
|
| 2118 |
|
| 2119 | |
| 2120 | * queue_me() - Enqueue the futex_q on the futex_hash_bucket
|
| 2121 | * @q: The futex_q to enqueue
|
| 2122 | * @hb: The destination hash bucket
|
| 2123 | *
|
| 2124 | * The hb->lock must be held by the caller, and is released here. A call to
|
| 2125 | * queue_me() is typically paired with exactly one call to unqueue_me(). The
|
| 2126 | * exceptions involve the PI related operations, which may use unqueue_me_pi()
|
| 2127 | * or nothing if the unqueue is done as part of the wake process and the unqueue
|
| 2128 | * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
|
| 2129 | * an example).
|
| 2130 |
|
| 2131 | static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
|
| 2132 | __releases(&hb->lock)
|
| 2133 | {
|
| 2134 | __queue_me(q, hb);
|
| 2135 | spin_unlock(&hb->lock);
|
| 2136 | }
|
| 2137 |
|
| 2138 | |
| 2139 | * unqueue_me() - Remove the futex_q from its futex_hash_bucket
|
| 2140 | * @q: The futex_q to unqueue
|
| 2141 | *
|
| 2142 | * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
|
| 2143 | * be paired with exactly one earlier call to queue_me().
|
| 2144 | *
|
| 2145 | * Return:
|
| 2146 | * - 1 - if the futex_q was still queued (and we removed unqueued it);
|
| 2147 | * - 0 - if the futex_q was already removed by the waking thread
|
| 2148 |
|
| 2149 | static int unqueue_me(struct futex_q *q)
|
| 2150 | {
|
| 2151 | spinlock_t *lock_ptr;
|
| 2152 | int ret = 0;
|
| 2153 |
|
| 2154 |
|
| 2155 | retry:
|
| 2156 | |
| 2157 | * q->lock_ptr can change between this read and the following spin_lock.
|
| 2158 | * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
|
| 2159 | * optimizing lock_ptr out of the logic below.
|
| 2160 |
|
| 2161 | lock_ptr = READ_ONCE(q->lock_ptr);
|
| 2162 | if (lock_ptr != NULL) {
|
| 2163 | spin_lock(lock_ptr);
|
| 2164 | |
| 2165 | * q->lock_ptr can change between reading it and
|
| 2166 | * spin_lock(), causing us to take the wrong lock. This
|
| 2167 | * corrects the race condition.
|
| 2168 | *
|
| 2169 | * Reasoning goes like this: if we have the wrong lock,
|
| 2170 | * q->lock_ptr must have changed (maybe several times)
|
| 2171 | * between reading it and the spin_lock(). It can
|
| 2172 | * change again after the spin_lock() but only if it was
|
| 2173 | * already changed before the spin_lock(). It cannot,
|
| 2174 | * however, change back to the original value. Therefore
|
| 2175 | * we can detect whether we acquired the correct lock.
|
| 2176 |
|
| 2177 | if (unlikely(lock_ptr != q->lock_ptr)) {
|
| 2178 | spin_unlock(lock_ptr);
|
| 2179 | goto retry;
|
| 2180 | }
|
| 2181 | __unqueue_futex(q);
|
| 2182 |
|
| 2183 | BUG_ON(q->pi_state);
|
| 2184 |
|
| 2185 | spin_unlock(lock_ptr);
|
| 2186 | ret = 1;
|
| 2187 | }
|
| 2188 |
|
| 2189 | drop_futex_key_refs(&q->key);
|
| 2190 | return ret;
|
| 2191 | }
|
| 2192 |
|
| 2193 | |
| 2194 | * PI futexes can not be requeued and must remove themself from the
|
| 2195 | * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
|
| 2196 | * and dropped here.
|
| 2197 |
|
| 2198 | static void unqueue_me_pi(struct futex_q *q)
|
| 2199 | __releases(q->lock_ptr)
|
| 2200 | {
|
| 2201 | __unqueue_futex(q);
|
| 2202 |
|
| 2203 | BUG_ON(!q->pi_state);
|
| 2204 | put_pi_state(q->pi_state);
|
| 2205 | q->pi_state = NULL;
|
| 2206 |
|
| 2207 | spin_unlock(q->lock_ptr);
|
| 2208 | }
|
| 2209 |
|
| 2210 | |
| 2211 | * Fixup the pi_state owner with the new owner.
|
| 2212 | *
|
| 2213 | * Must be called with hash bucket lock held and mm->sem held for non
|
| 2214 | * private futexes.
|
| 2215 |
|
| 2216 | static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
|
| 2217 | struct task_struct *newowner)
|
| 2218 | {
|
| 2219 | u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
|
| 2220 | struct futex_pi_state *pi_state = q->pi_state;
|
| 2221 | u32 uval, uninitialized_var(curval), newval;
|
| 2222 | struct task_struct *oldowner;
|
| 2223 | int ret;
|
| 2224 |
|
| 2225 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
|
| 2226 |
|
| 2227 | oldowner = pi_state->owner;
|
| 2228 |
|
| 2229 | if (!pi_state->owner)
|
| 2230 | newtid |= FUTEX_OWNER_DIED;
|
| 2231 |
|
| 2232 | |
| 2233 | * We are here either because we stole the rtmutex from the
|
| 2234 | * previous highest priority waiter or we are the highest priority
|
| 2235 | * waiter but have failed to get the rtmutex the first time.
|
| 2236 | *
|
| 2237 | * We have to replace the newowner TID in the user space variable.
|
| 2238 | * This must be atomic as we have to preserve the owner died bit here.
|
| 2239 | *
|
| 2240 | * Note: We write the user space value _before_ changing the pi_state
|
| 2241 | * because we can fault here. Imagine swapped out pages or a fork
|
| 2242 | * that marked all the anonymous memory readonly for cow.
|
| 2243 | *
|
| 2244 | * Modifying pi_state _before_ the user space value would leave the
|
| 2245 | * pi_state in an inconsistent state when we fault here, because we
|
| 2246 | * need to drop the locks to handle the fault. This might be observed
|
| 2247 | * in the PID check in lookup_pi_state.
|
| 2248 |
|
| 2249 | retry:
|
| 2250 | if (get_futex_value_locked(&uval, uaddr))
|
| 2251 | goto handle_fault;
|
| 2252 |
|
| 2253 | for (;;) {
|
| 2254 | newval = (uval & FUTEX_OWNER_DIED) | newtid;
|
| 2255 |
|
| 2256 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
|
| 2257 | goto handle_fault;
|
| 2258 | if (curval == uval)
|
| 2259 | break;
|
| 2260 | uval = curval;
|
| 2261 | }
|
| 2262 |
|
| 2263 | |
| 2264 | * We fixed up user space. Now we need to fix the pi_state
|
| 2265 | * itself.
|
| 2266 |
|
| 2267 | if (pi_state->owner != NULL) {
|
| 2268 | raw_spin_lock(&pi_state->owner->pi_lock);
|
| 2269 | WARN_ON(list_empty(&pi_state->list));
|
| 2270 | list_del_init(&pi_state->list);
|
| 2271 | raw_spin_unlock(&pi_state->owner->pi_lock);
|
| 2272 | }
|
| 2273 |
|
| 2274 | pi_state->owner = newowner;
|
| 2275 |
|
| 2276 | raw_spin_lock(&newowner->pi_lock);
|
| 2277 | WARN_ON(!list_empty(&pi_state->list));
|
| 2278 | list_add(&pi_state->list, &newowner->pi_state_list);
|
| 2279 | raw_spin_unlock(&newowner->pi_lock);
|
| 2280 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
| 2281 |
|
| 2282 | return 0;
|
| 2283 |
|
| 2284 | |
| 2285 | * To handle the page fault we need to drop the locks here. That gives
|
| 2286 | * the other task (either the highest priority waiter itself or the
|
| 2287 | * task which stole the rtmutex) the chance to try the fixup of the
|
| 2288 | * pi_state. So once we are back from handling the fault we need to
|
| 2289 | * check the pi_state after reacquiring the locks and before trying to
|
| 2290 | * do another fixup. When the fixup has been done already we simply
|
| 2291 | * return.
|
| 2292 | *
|
| 2293 | * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
|
| 2294 | * drop hb->lock since the caller owns the hb -> futex_q relation.
|
| 2295 | * Dropping the pi_mutex->wait_lock requires the state revalidate.
|
| 2296 |
|
| 2297 | handle_fault:
|
| 2298 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
| 2299 | spin_unlock(q->lock_ptr);
|
| 2300 |
|
| 2301 | ret = fault_in_user_writeable(uaddr);
|
| 2302 |
|
| 2303 | spin_lock(q->lock_ptr);
|
| 2304 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
|
| 2305 |
|
| 2306 | |
| 2307 | * Check if someone else fixed it for us:
|
| 2308 |
|
| 2309 | if (pi_state->owner != oldowner) {
|
| 2310 | ret = 0;
|
| 2311 | goto out_unlock;
|
| 2312 | }
|
| 2313 |
|
| 2314 | if (ret)
|
| 2315 | goto out_unlock;
|
| 2316 |
|
| 2317 | goto retry;
|
| 2318 |
|
| 2319 | out_unlock:
|
| 2320 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
| 2321 | return ret;
|
| 2322 | }
|
| 2323 |
|
| 2324 | static long futex_wait_restart(struct restart_block *restart);
|
| 2325 |
|
| 2326 | |
| 2327 | * fixup_owner() - Post lock pi_state and corner case management
|
| 2328 | * @uaddr: user address of the futex
|
| 2329 | * @q: futex_q (contains pi_state and access to the rt_mutex)
|
| 2330 | * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
|
| 2331 | *
|
| 2332 | * After attempting to lock an rt_mutex, this function is called to cleanup
|
| 2333 | * the pi_state owner as well as handle race conditions that may allow us to
|
| 2334 | * acquire the lock. Must be called with the hb lock held.
|
| 2335 | *
|
| 2336 | * Return:
|
| 2337 | * - 1 - success, lock taken;
|
| 2338 | * - 0 - success, lock not taken;
|
| 2339 | * - <0 - on error (-EFAULT)
|
| 2340 |
|
| 2341 | static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
|
| 2342 | {
|
| 2343 | int ret = 0;
|
| 2344 |
|
| 2345 | if (locked) {
|
| 2346 | |
| 2347 | * Got the lock. We might not be the anticipated owner if we
|
| 2348 | * did a lock-steal - fix up the PI-state in that case:
|
| 2349 | *
|
| 2350 | * We can safely read pi_state->owner without holding wait_lock
|
| 2351 | * because we now own the rt_mutex, only the owner will attempt
|
| 2352 | * to change it.
|
| 2353 |
|
| 2354 | if (q->pi_state->owner != current)
|
| 2355 | ret = fixup_pi_state_owner(uaddr, q, current);
|
| 2356 | goto out;
|
| 2357 | }
|
| 2358 |
|
| 2359 | |
| 2360 | * Paranoia check. If we did not take the lock, then we should not be
|
| 2361 | * the owner of the rt_mutex.
|
| 2362 |
|
| 2363 | if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) {
|
| 2364 | printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
|
| 2365 | "pi-state %p\n", ret,
|
| 2366 | q->pi_state->pi_mutex.owner,
|
| 2367 | q->pi_state->owner);
|
| 2368 | }
|
| 2369 |
|
| 2370 | out:
|
| 2371 | return ret ? ret : locked;
|
| 2372 | }
|
| 2373 |
|
| 2374 | |
| 2375 | * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
|
| 2376 | * @hb: the futex hash bucket, must be locked by the caller
|
| 2377 | * @q: the futex_q to queue up on
|
| 2378 | * @timeout: the prepared hrtimer_sleeper, or null for no timeout
|
| 2379 |
|
| 2380 | static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
|
| 2381 | struct hrtimer_sleeper *timeout)
|
| 2382 | {
|
| 2383 | |
| 2384 | * The task state is guaranteed to be set before another task can
|
| 2385 | * wake it. set_current_state() is implemented using smp_store_mb() and
|
| 2386 | * queue_me() calls spin_unlock() upon completion, both serializing
|
| 2387 | * access to the hash list and forcing another memory barrier.
|
| 2388 |
|
| 2389 | set_current_state(TASK_INTERRUPTIBLE);
|
| 2390 | queue_me(q, hb);
|
| 2391 |
|
| 2392 |
|
| 2393 | if (timeout)
|
| 2394 | hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
|
| 2395 |
|
| 2396 | |
| 2397 | * If we have been removed from the hash list, then another task
|
| 2398 | * has tried to wake us, and we can skip the call to schedule().
|
| 2399 |
|
| 2400 | if (likely(!plist_node_empty(&q->list))) {
|
| 2401 | |
| 2402 | * If the timer has already expired, current will already be
|
| 2403 | * flagged for rescheduling. Only call schedule if there
|
| 2404 | * is no timeout, or if it has yet to expire.
|
| 2405 |
|
| 2406 | if (!timeout || timeout->task)
|
| 2407 | freezable_schedule();
|
| 2408 | }
|
| 2409 | __set_current_state(TASK_RUNNING);
|
| 2410 | }
|
| 2411 |
|
| 2412 | |
| 2413 | * futex_wait_setup() - Prepare to wait on a futex
|
| 2414 | * @uaddr: the futex userspace address
|
| 2415 | * @val: the expected value
|
| 2416 | * @flags: futex flags (FLAGS_SHARED, etc.)
|
| 2417 | * @q: the associated futex_q
|
| 2418 | * @hb: storage for hash_bucket pointer to be returned to caller
|
| 2419 | *
|
| 2420 | * Setup the futex_q and locate the hash_bucket. Get the futex value and
|
| 2421 | * compare it with the expected value. Handle atomic faults internally.
|
| 2422 | * Return with the hb lock held and a q.key reference on success, and unlocked
|
| 2423 | * with no q.key reference on failure.
|
| 2424 | *
|
| 2425 | * Return:
|
| 2426 | * - 0 - uaddr contains val and hb has been locked;
|
| 2427 | * - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
|
| 2428 |
|
| 2429 | static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
|
| 2430 | struct futex_q *q, struct futex_hash_bucket **hb)
|
| 2431 | {
|
| 2432 | u32 uval;
|
| 2433 | int ret;
|
| 2434 |
|
| 2435 | |
| 2436 | * Access the page AFTER the hash-bucket is locked.
|
| 2437 | * Order is important:
|
| 2438 | *
|
| 2439 | * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
|
| 2440 | * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
|
| 2441 | *
|
| 2442 | * The basic logical guarantee of a futex is that it blocks ONLY
|
| 2443 | * if cond(var) is known to be true at the time of blocking, for
|
| 2444 | * any cond. If we locked the hash-bucket after testing *uaddr, that
|
| 2445 | * would open a race condition where we could block indefinitely with
|
| 2446 | * cond(var) false, which would violate the guarantee.
|
| 2447 | *
|
| 2448 | * On the other hand, we insert q and release the hash-bucket only
|
| 2449 | * after testing *uaddr. This guarantees that futex_wait() will NOT
|
| 2450 | * absorb a wakeup if *uaddr does not match the desired values
|
| 2451 | * while the syscall executes.
|
| 2452 |
|
| 2453 | retry:
|
| 2454 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
|
| 2455 | if (unlikely(ret != 0))
|
| 2456 | return ret;
|
| 2457 |
|
| 2458 | retry_private:
|
| 2459 | *hb = queue_lock(q);
|
| 2460 |
|
| 2461 | ret = get_futex_value_locked(&uval, uaddr);
|
| 2462 |
|
| 2463 | if (ret) {
|
| 2464 | queue_unlock(*hb);
|
| 2465 |
|
| 2466 | ret = get_user(uval, uaddr);
|
| 2467 | if (ret)
|
| 2468 | goto out;
|
| 2469 |
|
| 2470 | if (!(flags & FLAGS_SHARED))
|
| 2471 | goto retry_private;
|
| 2472 |
|
| 2473 | put_futex_key(&q->key);
|
| 2474 | goto retry;
|
| 2475 | }
|
| 2476 |
|
| 2477 | if (uval != val) {
|
| 2478 | queue_unlock(*hb);
|
| 2479 | ret = -EWOULDBLOCK;
|
| 2480 | }
|
| 2481 |
|
| 2482 | out:
|
| 2483 | if (ret)
|
| 2484 | put_futex_key(&q->key);
|
| 2485 | return ret;
|
| 2486 | }
|
| 2487 |
|
| 2488 | static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
|
| 2489 | ktime_t *abs_time, u32 bitset)
|
| 2490 | {
|
| 2491 | struct hrtimer_sleeper timeout, *to = NULL;
|
| 2492 | struct restart_block *restart;
|
| 2493 | struct futex_hash_bucket *hb;
|
| 2494 | struct futex_q q = futex_q_init;
|
| 2495 | int ret;
|
| 2496 |
|
| 2497 | if (!bitset)
|
| 2498 | return -EINVAL;
|
| 2499 | q.bitset = bitset;
|
| 2500 |
|
| 2501 | if (abs_time) {
|
| 2502 | to = &timeout;
|
| 2503 |
|
| 2504 | hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
|
| 2505 | CLOCK_REALTIME : CLOCK_MONOTONIC,
|
| 2506 | HRTIMER_MODE_ABS);
|
| 2507 | hrtimer_init_sleeper(to, current);
|
| 2508 | hrtimer_set_expires_range_ns(&to->timer, *abs_time,
|
| 2509 | current->timer_slack_ns);
|
| 2510 | }
|
| 2511 |
|
| 2512 | retry:
|
| 2513 | |
| 2514 | * Prepare to wait on uaddr. On success, holds hb lock and increments
|
| 2515 | * q.key refs.
|
| 2516 |
|
| 2517 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
|
| 2518 | if (ret)
|
| 2519 | goto out;
|
| 2520 |
|
| 2521 |
|
| 2522 | futex_wait_queue_me(hb, &q, to);
|
| 2523 |
|
| 2524 |
|
| 2525 | ret = 0;
|
| 2526 |
|
| 2527 | if (!unqueue_me(&q))
|
| 2528 | goto out;
|
| 2529 | ret = -ETIMEDOUT;
|
| 2530 | if (to && !to->task)
|
| 2531 | goto out;
|
| 2532 |
|
| 2533 | |
| 2534 | * We expect signal_pending(current), but we might be the
|
| 2535 | * victim of a spurious wakeup as well.
|
| 2536 |
|
| 2537 | if (!signal_pending(current))
|
| 2538 | goto retry;
|
| 2539 |
|
| 2540 | ret = -ERESTARTSYS;
|
| 2541 | if (!abs_time)
|
| 2542 | goto out;
|
| 2543 |
|
| 2544 | restart = ¤t->restart_block;
|
| 2545 | restart->fn = futex_wait_restart;
|
| 2546 | restart->futex.uaddr = uaddr;
|
| 2547 | restart->futex.val = val;
|
| 2548 | restart->futex.time = *abs_time;
|
| 2549 | restart->futex.bitset = bitset;
|
| 2550 | restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
|
| 2551 |
|
| 2552 | ret = -ERESTART_RESTARTBLOCK;
|
| 2553 |
|
| 2554 | out:
|
| 2555 | if (to) {
|
| 2556 | hrtimer_cancel(&to->timer);
|
| 2557 | destroy_hrtimer_on_stack(&to->timer);
|
| 2558 | }
|
| 2559 | return ret;
|
| 2560 | }
|
| 2561 |
|
| 2562 |
|
| 2563 | static long futex_wait_restart(struct restart_block *restart)
|
| 2564 | {
|
| 2565 | u32 __user *uaddr = restart->futex.uaddr;
|
| 2566 | ktime_t t, *tp = NULL;
|
| 2567 |
|
| 2568 | if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
|
| 2569 | t = restart->futex.time;
|
| 2570 | tp = &t;
|
| 2571 | }
|
| 2572 | restart->fn = do_no_restart_syscall;
|
| 2573 |
|
| 2574 | return (long)futex_wait(uaddr, restart->futex.flags,
|
| 2575 | restart->futex.val, tp, restart->futex.bitset);
|
| 2576 | }
|
| 2577 |
|
| 2578 |
|
| 2579 | |
| 2580 | * Userspace tried a 0 -> TID atomic transition of the futex value
|
| 2581 | * and failed. The kernel side here does the whole locking operation:
|
| 2582 | * if there are waiters then it will block as a consequence of relying
|
| 2583 | * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
|
| 2584 | * a 0 value of the futex too.).
|
| 2585 | *
|
| 2586 | * Also serves as futex trylock_pi()'ing, and due semantics.
|
| 2587 |
|
| 2588 | static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
|
| 2589 | ktime_t *time, int trylock)
|
| 2590 | {
|
| 2591 | struct hrtimer_sleeper timeout, *to = NULL;
|
| 2592 | struct futex_pi_state *pi_state = NULL;
|
| 2593 | struct rt_mutex_waiter rt_waiter;
|
| 2594 | struct futex_hash_bucket *hb;
|
| 2595 | struct futex_q q = futex_q_init;
|
| 2596 | int res, ret;
|
| 2597 |
|
| 2598 | if (refill_pi_state_cache())
|
| 2599 | return -ENOMEM;
|
| 2600 |
|
| 2601 | if (time) {
|
| 2602 | to = &timeout;
|
| 2603 | hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
|
| 2604 | HRTIMER_MODE_ABS);
|
| 2605 | hrtimer_init_sleeper(to, current);
|
| 2606 | hrtimer_set_expires(&to->timer, *time);
|
| 2607 | }
|
| 2608 |
|
| 2609 | retry:
|
| 2610 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
|
| 2611 | if (unlikely(ret != 0))
|
| 2612 | goto out;
|
| 2613 |
|
| 2614 | retry_private:
|
| 2615 | hb = queue_lock(&q);
|
| 2616 |
|
| 2617 | ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
|
| 2618 | if (unlikely(ret)) {
|
| 2619 | |
| 2620 | * Atomic work succeeded and we got the lock,
|
| 2621 | * or failed. Either way, we do _not_ block.
|
| 2622 |
|
| 2623 | switch (ret) {
|
| 2624 | case 1:
|
| 2625 |
|
| 2626 | ret = 0;
|
| 2627 | goto out_unlock_put_key;
|
| 2628 | case -EFAULT:
|
| 2629 | goto uaddr_faulted;
|
| 2630 | case -EAGAIN:
|
| 2631 | |
| 2632 | * Two reasons for this:
|
| 2633 | * - Task is exiting and we just wait for the
|
| 2634 | * exit to complete.
|
| 2635 | * - The user space value changed.
|
| 2636 |
|
| 2637 | queue_unlock(hb);
|
| 2638 | put_futex_key(&q.key);
|
| 2639 | cond_resched();
|
| 2640 | goto retry;
|
| 2641 | default:
|
| 2642 | goto out_unlock_put_key;
|
| 2643 | }
|
| 2644 | }
|
| 2645 |
|
| 2646 | WARN_ON(!q.pi_state);
|
| 2647 |
|
| 2648 | |
| 2649 | * Only actually queue now that the atomic ops are done:
|
| 2650 |
|
| 2651 | __queue_me(&q, hb);
|
| 2652 |
|
| 2653 | if (trylock) {
|
| 2654 | ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
|
| 2655 |
|
| 2656 | ret = ret ? 0 : -EWOULDBLOCK;
|
| 2657 | goto no_block;
|
| 2658 | }
|
| 2659 |
|
| 2660 | rt_mutex_init_waiter(&rt_waiter);
|
| 2661 |
|
| 2662 | |
| 2663 | * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
|
| 2664 | * hold it while doing rt_mutex_start_proxy(), because then it will
|
| 2665 | * include hb->lock in the blocking chain, even through we'll not in
|
| 2666 | * fact hold it while blocking. This will lead it to report -EDEADLK
|
| 2667 | * and BUG when futex_unlock_pi() interleaves with this.
|
| 2668 | *
|
| 2669 | * Therefore acquire wait_lock while holding hb->lock, but drop the
|
| 2670 | * latter before calling rt_mutex_start_proxy_lock(). This still fully
|
| 2671 | * serializes against futex_unlock_pi() as that does the exact same
|
| 2672 | * lock handoff sequence.
|
| 2673 |
|
| 2674 | raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
|
| 2675 | spin_unlock(q.lock_ptr);
|
| 2676 | ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
|
| 2677 | raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
|
| 2678 |
|
| 2679 | if (ret) {
|
| 2680 | if (ret == 1)
|
| 2681 | ret = 0;
|
| 2682 |
|
| 2683 | spin_lock(q.lock_ptr);
|
| 2684 | goto no_block;
|
| 2685 | }
|
| 2686 |
|
| 2687 |
|
| 2688 | if (unlikely(to))
|
| 2689 | hrtimer_start_expires(&to->timer, HRTIMER_MODE_ABS);
|
| 2690 |
|
| 2691 | ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
|
| 2692 |
|
| 2693 | spin_lock(q.lock_ptr);
|
| 2694 | |
| 2695 | * If we failed to acquire the lock (signal/timeout), we must
|
| 2696 | * first acquire the hb->lock before removing the lock from the
|
| 2697 | * rt_mutex waitqueue, such that we can keep the hb and rt_mutex
|
| 2698 | * wait lists consistent.
|
| 2699 | *
|
| 2700 | * In particular; it is important that futex_unlock_pi() can not
|
| 2701 | * observe this inconsistency.
|
| 2702 |
|
| 2703 | if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
|
| 2704 | ret = 0;
|
| 2705 |
|
| 2706 | no_block:
|
| 2707 | |
| 2708 | * Fixup the pi_state owner and possibly acquire the lock if we
|
| 2709 | * haven't already.
|
| 2710 |
|
| 2711 | res = fixup_owner(uaddr, &q, !ret);
|
| 2712 | |
| 2713 | * If fixup_owner() returned an error, proprogate that. If it acquired
|
| 2714 | * the lock, clear our -ETIMEDOUT or -EINTR.
|
| 2715 |
|
| 2716 | if (res)
|
| 2717 | ret = (res < 0) ? res : 0;
|
| 2718 |
|
| 2719 | |
| 2720 | * If fixup_owner() faulted and was unable to handle the fault, unlock
|
| 2721 | * it and return the fault to userspace.
|
| 2722 |
|
| 2723 | if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) {
|
| 2724 | pi_state = q.pi_state;
|
| 2725 | get_pi_state(pi_state);
|
| 2726 | }
|
| 2727 |
|
| 2728 |
|
| 2729 | unqueue_me_pi(&q);
|
| 2730 |
|
| 2731 | if (pi_state) {
|
| 2732 | rt_mutex_futex_unlock(&pi_state->pi_mutex);
|
| 2733 | put_pi_state(pi_state);
|
| 2734 | }
|
| 2735 |
|
| 2736 | goto out_put_key;
|
| 2737 |
|
| 2738 | out_unlock_put_key:
|
| 2739 | queue_unlock(hb);
|
| 2740 |
|
| 2741 | out_put_key:
|
| 2742 | put_futex_key(&q.key);
|
| 2743 | out:
|
| 2744 | if (to) {
|
| 2745 | hrtimer_cancel(&to->timer);
|
| 2746 | destroy_hrtimer_on_stack(&to->timer);
|
| 2747 | }
|
| 2748 | return ret != -EINTR ? ret : -ERESTARTNOINTR;
|
| 2749 |
|
| 2750 | uaddr_faulted:
|
| 2751 | queue_unlock(hb);
|
| 2752 |
|
| 2753 | ret = fault_in_user_writeable(uaddr);
|
| 2754 | if (ret)
|
| 2755 | goto out_put_key;
|
| 2756 |
|
| 2757 | if (!(flags & FLAGS_SHARED))
|
| 2758 | goto retry_private;
|
| 2759 |
|
| 2760 | put_futex_key(&q.key);
|
| 2761 | goto retry;
|
| 2762 | }
|
| 2763 |
|
| 2764 | |
| 2765 | * Userspace attempted a TID -> 0 atomic transition, and failed.
|
| 2766 | * This is the in-kernel slowpath: we look up the PI state (if any),
|
| 2767 | * and do the rt-mutex unlock.
|
| 2768 |
|
| 2769 | static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
|
| 2770 | {
|
| 2771 | u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
|
| 2772 | union futex_key key = FUTEX_KEY_INIT;
|
| 2773 | struct futex_hash_bucket *hb;
|
| 2774 | struct futex_q *top_waiter;
|
| 2775 | int ret;
|
| 2776 |
|
| 2777 | retry:
|
| 2778 | if (get_user(uval, uaddr))
|
| 2779 | return -EFAULT;
|
| 2780 | |
| 2781 | * We release only a lock we actually own:
|
| 2782 |
|
| 2783 | if ((uval & FUTEX_TID_MASK) != vpid)
|
| 2784 | return -EPERM;
|
| 2785 |
|
| 2786 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
|
| 2787 | if (ret)
|
| 2788 | return ret;
|
| 2789 |
|
| 2790 | hb = hash_futex(&key);
|
| 2791 | spin_lock(&hb->lock);
|
| 2792 |
|
| 2793 | |
| 2794 | * Check waiters first. We do not trust user space values at
|
| 2795 | * all and we at least want to know if user space fiddled
|
| 2796 | * with the futex value instead of blindly unlocking.
|
| 2797 |
|
| 2798 | top_waiter = futex_top_waiter(hb, &key);
|
| 2799 | if (top_waiter) {
|
| 2800 | struct futex_pi_state *pi_state = top_waiter->pi_state;
|
| 2801 |
|
| 2802 | ret = -EINVAL;
|
| 2803 | if (!pi_state)
|
| 2804 | goto out_unlock;
|
| 2805 |
|
| 2806 | |
| 2807 | * If current does not own the pi_state then the futex is
|
| 2808 | * inconsistent and user space fiddled with the futex value.
|
| 2809 |
|
| 2810 | if (pi_state->owner != current)
|
| 2811 | goto out_unlock;
|
| 2812 |
|
| 2813 | get_pi_state(pi_state);
|
| 2814 | |
| 2815 | * By taking wait_lock while still holding hb->lock, we ensure
|
| 2816 | * there is no point where we hold neither; and therefore
|
| 2817 | * wake_futex_pi() must observe a state consistent with what we
|
| 2818 | * observed.
|
| 2819 |
|
| 2820 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
|
| 2821 | spin_unlock(&hb->lock);
|
| 2822 |
|
| 2823 | ret = wake_futex_pi(uaddr, uval, pi_state);
|
| 2824 |
|
| 2825 | put_pi_state(pi_state);
|
| 2826 |
|
| 2827 | |
| 2828 | * Success, we're done! No tricky corner cases.
|
| 2829 |
|
| 2830 | if (!ret)
|
| 2831 | goto out_putkey;
|
| 2832 | |
| 2833 | * The atomic access to the futex value generated a
|
| 2834 | * pagefault, so retry the user-access and the wakeup:
|
| 2835 |
|
| 2836 | if (ret == -EFAULT)
|
| 2837 | goto pi_faulted;
|
| 2838 | |
| 2839 | * A unconditional UNLOCK_PI op raced against a waiter
|
| 2840 | * setting the FUTEX_WAITERS bit. Try again.
|
| 2841 |
|
| 2842 | if (ret == -EAGAIN) {
|
| 2843 | put_futex_key(&key);
|
| 2844 | goto retry;
|
| 2845 | }
|
| 2846 | |
| 2847 | * wake_futex_pi has detected invalid state. Tell user
|
| 2848 | * space.
|
| 2849 |
|
| 2850 | goto out_putkey;
|
| 2851 | }
|
| 2852 |
|
| 2853 | |
| 2854 | * We have no kernel internal state, i.e. no waiters in the
|
| 2855 | * kernel. Waiters which are about to queue themselves are stuck
|
| 2856 | * on hb->lock. So we can safely ignore them. We do neither
|
| 2857 | * preserve the WAITERS bit not the OWNER_DIED one. We are the
|
| 2858 | * owner.
|
| 2859 |
|
| 2860 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0)) {
|
| 2861 | spin_unlock(&hb->lock);
|
| 2862 | goto pi_faulted;
|
| 2863 | }
|
| 2864 |
|
| 2865 | |
| 2866 | * If uval has changed, let user space handle it.
|
| 2867 |
|
| 2868 | ret = (curval == uval) ? 0 : -EAGAIN;
|
| 2869 |
|
| 2870 | out_unlock:
|
| 2871 | spin_unlock(&hb->lock);
|
| 2872 | out_putkey:
|
| 2873 | put_futex_key(&key);
|
| 2874 | return ret;
|
| 2875 |
|
| 2876 | pi_faulted:
|
| 2877 | put_futex_key(&key);
|
| 2878 |
|
| 2879 | ret = fault_in_user_writeable(uaddr);
|
| 2880 | if (!ret)
|
| 2881 | goto retry;
|
| 2882 |
|
| 2883 | return ret;
|
| 2884 | }
|
| 2885 |
|
| 2886 | |
| 2887 | * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
|
| 2888 | * @hb: the hash_bucket futex_q was original enqueued on
|
| 2889 | * @q: the futex_q woken while waiting to be requeued
|
| 2890 | * @key2: the futex_key of the requeue target futex
|
| 2891 | * @timeout: the timeout associated with the wait (NULL if none)
|
| 2892 | *
|
| 2893 | * Detect if the task was woken on the initial futex as opposed to the requeue
|
| 2894 | * target futex. If so, determine if it was a timeout or a signal that caused
|
| 2895 | * the wakeup and return the appropriate error code to the caller. Must be
|
| 2896 | * called with the hb lock held.
|
| 2897 | *
|
| 2898 | * Return:
|
| 2899 | * - 0 = no early wakeup detected;
|
| 2900 | * - <0 = -ETIMEDOUT or -ERESTARTNOINTR
|
| 2901 |
|
| 2902 | static inline
|
| 2903 | int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
|
| 2904 | struct futex_q *q, union futex_key *key2,
|
| 2905 | struct hrtimer_sleeper *timeout)
|
| 2906 | {
|
| 2907 | int ret = 0;
|
| 2908 |
|
| 2909 | |
| 2910 | * With the hb lock held, we avoid races while we process the wakeup.
|
| 2911 | * We only need to hold hb (and not hb2) to ensure atomicity as the
|
| 2912 | * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
|
| 2913 | * It can't be requeued from uaddr2 to something else since we don't
|
| 2914 | * support a PI aware source futex for requeue.
|
| 2915 |
|
| 2916 | if (!match_futex(&q->key, key2)) {
|
| 2917 | WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
|
| 2918 | |
| 2919 | * We were woken prior to requeue by a timeout or a signal.
|
| 2920 | * Unqueue the futex_q and determine which it was.
|
| 2921 |
|
| 2922 | plist_del(&q->list, &hb->chain);
|
| 2923 | hb_waiters_dec(hb);
|
| 2924 |
|
| 2925 |
|
| 2926 | ret = -EWOULDBLOCK;
|
| 2927 | if (timeout && !timeout->task)
|
| 2928 | ret = -ETIMEDOUT;
|
| 2929 | else if (signal_pending(current))
|
| 2930 | ret = -ERESTARTNOINTR;
|
| 2931 | }
|
| 2932 | return ret;
|
| 2933 | }
|
| 2934 |
|
| 2935 | |
| 2936 | * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
|
| 2937 | * @uaddr: the futex we initially wait on (non-pi)
|
| 2938 | * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
|
| 2939 | * the same type, no requeueing from private to shared, etc.
|
| 2940 | * @val: the expected value of uaddr
|
| 2941 | * @abs_time: absolute timeout
|
| 2942 | * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
|
| 2943 | * @uaddr2: the pi futex we will take prior to returning to user-space
|
| 2944 | *
|
| 2945 | * The caller will wait on uaddr and will be requeued by futex_requeue() to
|
| 2946 | * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
|
| 2947 | * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
|
| 2948 | * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
|
| 2949 | * without one, the pi logic would not know which task to boost/deboost, if
|
| 2950 | * there was a need to.
|
| 2951 | *
|
| 2952 | * We call schedule in futex_wait_queue_me() when we enqueue and return there
|
| 2953 | * via the following--
|
| 2954 | * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
|
| 2955 | * 2) wakeup on uaddr2 after a requeue
|
| 2956 | * 3) signal
|
| 2957 | * 4) timeout
|
| 2958 | *
|
| 2959 | * If 3, cleanup and return -ERESTARTNOINTR.
|
| 2960 | *
|
| 2961 | * If 2, we may then block on trying to take the rt_mutex and return via:
|
| 2962 | * 5) successful lock
|
| 2963 | * 6) signal
|
| 2964 | * 7) timeout
|
| 2965 | * 8) other lock acquisition failure
|
| 2966 | *
|
| 2967 | * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
|
| 2968 | *
|
| 2969 | * If 4 or 7, we cleanup and return with -ETIMEDOUT.
|
| 2970 | *
|
| 2971 | * Return:
|
| 2972 | * - 0 - On success;
|
| 2973 | * - <0 - On error
|
| 2974 |
|
| 2975 | static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
|
| 2976 | u32 val, ktime_t *abs_time, u32 bitset,
|
| 2977 | u32 __user *uaddr2)
|
| 2978 | {
|
| 2979 | struct hrtimer_sleeper timeout, *to = NULL;
|
| 2980 | struct futex_pi_state *pi_state = NULL;
|
| 2981 | struct rt_mutex_waiter rt_waiter;
|
| 2982 | struct futex_hash_bucket *hb;
|
| 2983 | union futex_key key2 = FUTEX_KEY_INIT;
|
| 2984 | struct futex_q q = futex_q_init;
|
| 2985 | int res, ret;
|
| 2986 |
|
| 2987 | if (uaddr == uaddr2)
|
| 2988 | return -EINVAL;
|
| 2989 |
|
| 2990 | if (!bitset)
|
| 2991 | return -EINVAL;
|
| 2992 |
|
| 2993 | if (abs_time) {
|
| 2994 | to = &timeout;
|
| 2995 | hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
|
| 2996 | CLOCK_REALTIME : CLOCK_MONOTONIC,
|
| 2997 | HRTIMER_MODE_ABS);
|
| 2998 | hrtimer_init_sleeper(to, current);
|
| 2999 | hrtimer_set_expires_range_ns(&to->timer, *abs_time,
|
| 3000 | current->timer_slack_ns);
|
| 3001 | }
|
| 3002 |
|
| 3003 | |
| 3004 | * The waiter is allocated on our stack, manipulated by the requeue
|
| 3005 | * code while we sleep on uaddr.
|
| 3006 |
|
| 3007 | rt_mutex_init_waiter(&rt_waiter);
|
| 3008 |
|
| 3009 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
|
| 3010 | if (unlikely(ret != 0))
|
| 3011 | goto out;
|
| 3012 |
|
| 3013 | q.bitset = bitset;
|
| 3014 | q.rt_waiter = &rt_waiter;
|
| 3015 | q.requeue_pi_key = &key2;
|
| 3016 |
|
| 3017 | |
| 3018 | * Prepare to wait on uaddr. On success, increments q.key (key1) ref
|
| 3019 | * count.
|
| 3020 |
|
| 3021 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
|
| 3022 | if (ret)
|
| 3023 | goto out_key2;
|
| 3024 |
|
| 3025 | |
| 3026 | * The check above which compares uaddrs is not sufficient for
|
| 3027 | * shared futexes. We need to compare the keys:
|
| 3028 |
|
| 3029 | if (match_futex(&q.key, &key2)) {
|
| 3030 | queue_unlock(hb);
|
| 3031 | ret = -EINVAL;
|
| 3032 | goto out_put_keys;
|
| 3033 | }
|
| 3034 |
|
| 3035 |
|
| 3036 | futex_wait_queue_me(hb, &q, to);
|
| 3037 |
|
| 3038 | spin_lock(&hb->lock);
|
| 3039 | ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
|
| 3040 | spin_unlock(&hb->lock);
|
| 3041 | if (ret)
|
| 3042 | goto out_put_keys;
|
| 3043 |
|
| 3044 | |
| 3045 | * In order for us to be here, we know our q.key == key2, and since
|
| 3046 | * we took the hb->lock above, we also know that futex_requeue() has
|
| 3047 | * completed and we no longer have to concern ourselves with a wakeup
|
| 3048 | * race with the atomic proxy lock acquisition by the requeue code. The
|
| 3049 | * futex_requeue dropped our key1 reference and incremented our key2
|
| 3050 | * reference count.
|
| 3051 |
|
| 3052 |
|
| 3053 |
|
| 3054 | if (!q.rt_waiter) {
|
| 3055 | |
| 3056 | * Got the lock. We might not be the anticipated owner if we
|
| 3057 | * did a lock-steal - fix up the PI-state in that case.
|
| 3058 |
|
| 3059 | if (q.pi_state && (q.pi_state->owner != current)) {
|
| 3060 | spin_lock(q.lock_ptr);
|
| 3061 | ret = fixup_pi_state_owner(uaddr2, &q, current);
|
| 3062 | if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
|
| 3063 | pi_state = q.pi_state;
|
| 3064 | get_pi_state(pi_state);
|
| 3065 | }
|
| 3066 | |
| 3067 | * Drop the reference to the pi state which
|
| 3068 | * the requeue_pi() code acquired for us.
|
| 3069 |
|
| 3070 | put_pi_state(q.pi_state);
|
| 3071 | spin_unlock(q.lock_ptr);
|
| 3072 | }
|
| 3073 | } else {
|
| 3074 | struct rt_mutex *pi_mutex;
|
| 3075 |
|
| 3076 | |
| 3077 | * We have been woken up by futex_unlock_pi(), a timeout, or a
|
| 3078 | * signal. futex_unlock_pi() will not destroy the lock_ptr nor
|
| 3079 | * the pi_state.
|
| 3080 |
|
| 3081 | WARN_ON(!q.pi_state);
|
| 3082 | pi_mutex = &q.pi_state->pi_mutex;
|
| 3083 | ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
|
| 3084 |
|
| 3085 | spin_lock(q.lock_ptr);
|
| 3086 | if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
|
| 3087 | ret = 0;
|
| 3088 |
|
| 3089 | debug_rt_mutex_free_waiter(&rt_waiter);
|
| 3090 | |
| 3091 | * Fixup the pi_state owner and possibly acquire the lock if we
|
| 3092 | * haven't already.
|
| 3093 |
|
| 3094 | res = fixup_owner(uaddr2, &q, !ret);
|
| 3095 | |
| 3096 | * If fixup_owner() returned an error, proprogate that. If it
|
| 3097 | * acquired the lock, clear -ETIMEDOUT or -EINTR.
|
| 3098 |
|
| 3099 | if (res)
|
| 3100 | ret = (res < 0) ? res : 0;
|
| 3101 |
|
| 3102 | |
| 3103 | * If fixup_pi_state_owner() faulted and was unable to handle
|
| 3104 | * the fault, unlock the rt_mutex and return the fault to
|
| 3105 | * userspace.
|
| 3106 |
|
| 3107 | if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
|
| 3108 | pi_state = q.pi_state;
|
| 3109 | get_pi_state(pi_state);
|
| 3110 | }
|
| 3111 |
|
| 3112 |
|
| 3113 | unqueue_me_pi(&q);
|
| 3114 | }
|
| 3115 |
|
| 3116 | if (pi_state) {
|
| 3117 | rt_mutex_futex_unlock(&pi_state->pi_mutex);
|
| 3118 | put_pi_state(pi_state);
|
| 3119 | }
|
| 3120 |
|
| 3121 | if (ret == -EINTR) {
|
| 3122 | |
| 3123 | * We've already been requeued, but cannot restart by calling
|
| 3124 | * futex_lock_pi() directly. We could restart this syscall, but
|
| 3125 | * it would detect that the user space "val" changed and return
|
| 3126 | * -EWOULDBLOCK. Save the overhead of the restart and return
|
| 3127 | * -EWOULDBLOCK directly.
|
| 3128 |
|
| 3129 | ret = -EWOULDBLOCK;
|
| 3130 | }
|
| 3131 |
|
| 3132 | out_put_keys:
|
| 3133 | put_futex_key(&q.key);
|
| 3134 | out_key2:
|
| 3135 | put_futex_key(&key2);
|
| 3136 |
|
| 3137 | out:
|
| 3138 | if (to) {
|
| 3139 | hrtimer_cancel(&to->timer);
|
| 3140 | destroy_hrtimer_on_stack(&to->timer);
|
| 3141 | }
|
| 3142 | return ret;
|
| 3143 | }
|
| 3144 |
|
| 3145 | |
| 3146 | * Support for robust futexes: the kernel cleans up held futexes at
|
| 3147 | * thread exit time.
|
| 3148 | *
|
| 3149 | * Implementation: user-space maintains a per-thread list of locks it
|
| 3150 | * is holding. Upon do_exit(), the kernel carefully walks this list,
|
| 3151 | * and marks all locks that are owned by this thread with the
|
| 3152 | * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
|
| 3153 | * always manipulated with the lock held, so the list is private and
|
| 3154 | * per-thread. Userspace also maintains a per-thread 'list_op_pending'
|
| 3155 | * field, to allow the kernel to clean up if the thread dies after
|
| 3156 | * acquiring the lock, but just before it could have added itself to
|
| 3157 | * the list. There can only be one such pending lock.
|
| 3158 |
|
| 3159 |
|
| 3160 | |
| 3161 | * sys_set_robust_list() - Set the robust-futex list head of a task
|
| 3162 | * @head: pointer to the list-head
|
| 3163 | * @len: length of the list-head, as userspace expects
|
| 3164 |
|
| 3165 | SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
|
| 3166 | size_t, len)
|
| 3167 | {
|
| 3168 | if (!futex_cmpxchg_enabled)
|
| 3169 | return -ENOSYS;
|
| 3170 | |
| 3171 | * The kernel knows only one size for now:
|
| 3172 |
|
| 3173 | if (unlikely(len != sizeof(*head)))
|
| 3174 | return -EINVAL;
|
| 3175 |
|
| 3176 | current->robust_list = head;
|
| 3177 |
|
| 3178 | return 0;
|
| 3179 | }
|
| 3180 |
|
| 3181 | |
| 3182 | * sys_get_robust_list() - Get the robust-futex list head of a task
|
| 3183 | * @pid: pid of the process [zero for current task]
|
| 3184 | * @head_ptr: pointer to a list-head pointer, the kernel fills it in
|
| 3185 | * @len_ptr: pointer to a length field, the kernel fills in the header size
|
| 3186 |
|
| 3187 | SYSCALL_DEFINE3(get_robust_list, int, pid,
|
| 3188 | struct robust_list_head __user * __user *, head_ptr,
|
| 3189 | size_t __user *, len_ptr)
|
| 3190 | {
|
| 3191 | struct robust_list_head __user *head;
|
| 3192 | unsigned long ret;
|
| 3193 | struct task_struct *p;
|
| 3194 |
|
| 3195 | if (!futex_cmpxchg_enabled)
|
| 3196 | return -ENOSYS;
|
| 3197 |
|
| 3198 | rcu_read_lock();
|
| 3199 |
|
| 3200 | ret = -ESRCH;
|
| 3201 | if (!pid)
|
| 3202 | p = current;
|
| 3203 | else {
|
| 3204 | p = find_task_by_vpid(pid);
|
| 3205 | if (!p)
|
| 3206 | goto err_unlock;
|
| 3207 | }
|
| 3208 |
|
| 3209 | ret = -EPERM;
|
| 3210 | if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
|
| 3211 | goto err_unlock;
|
| 3212 |
|
| 3213 | head = p->robust_list;
|
| 3214 | rcu_read_unlock();
|
| 3215 |
|
| 3216 | if (put_user(sizeof(*head), len_ptr))
|
| 3217 | return -EFAULT;
|
| 3218 | return put_user(head, head_ptr);
|
| 3219 |
|
| 3220 | err_unlock:
|
| 3221 | rcu_read_unlock();
|
| 3222 |
|
| 3223 | return ret;
|
| 3224 | }
|
| 3225 |
|
| 3226 | |
| 3227 | * Process a futex-list entry, check whether it's owned by the
|
| 3228 | * dying task, and do notification if so:
|
| 3229 |
|
| 3230 | int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
|
| 3231 | {
|
| 3232 | u32 uval, uninitialized_var(nval), mval;
|
| 3233 |
|
| 3234 | retry:
|
| 3235 | if (get_user(uval, uaddr))
|
| 3236 | return -1;
|
| 3237 |
|
| 3238 | if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
|
| 3239 | |
| 3240 | * Ok, this dying thread is truly holding a futex
|
| 3241 | * of interest. Set the OWNER_DIED bit atomically
|
| 3242 | * via cmpxchg, and if the value had FUTEX_WAITERS
|
| 3243 | * set, wake up a waiter (if any). (We have to do a
|
| 3244 | * futex_wake() even if OWNER_DIED is already set -
|
| 3245 | * to handle the rare but possible case of recursive
|
| 3246 | * thread-death.) The rest of the cleanup is done in
|
| 3247 | * userspace.
|
| 3248 |
|
| 3249 | mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
|
| 3250 | |
| 3251 | * We are not holding a lock here, but we want to have
|
| 3252 | * the pagefault_disable/enable() protection because
|
| 3253 | * we want to handle the fault gracefully. If the
|
| 3254 | * access fails we try to fault in the futex with R/W
|
| 3255 | * verification via get_user_pages. get_user() above
|
| 3256 | * does not guarantee R/W access. If that fails we
|
| 3257 | * give up and leave the futex locked.
|
| 3258 |
|
| 3259 | if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
|
| 3260 | if (fault_in_user_writeable(uaddr))
|
| 3261 | return -1;
|
| 3262 | goto retry;
|
| 3263 | }
|
| 3264 | if (nval != uval)
|
| 3265 | goto retry;
|
| 3266 |
|
| 3267 | |
| 3268 | * Wake robust non-PI futexes here. The wakeup of
|
| 3269 | * PI futexes happens in exit_pi_state():
|
| 3270 |
|
| 3271 | if (!pi && (uval & FUTEX_WAITERS))
|
| 3272 | futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
|
| 3273 | }
|
| 3274 | return 0;
|
| 3275 | }
|
| 3276 |
|
| 3277 | |
| 3278 | * Fetch a robust-list pointer. Bit 0 signals PI futexes:
|
| 3279 |
|
| 3280 | static inline int fetch_robust_entry(struct robust_list __user **entry,
|
| 3281 | struct robust_list __user * __user *head,
|
| 3282 | unsigned int *pi)
|
| 3283 | {
|
| 3284 | unsigned long uentry;
|
| 3285 |
|
| 3286 | if (get_user(uentry, (unsigned long __user *)head))
|
| 3287 | return -EFAULT;
|
| 3288 |
|
| 3289 | *entry = (void __user *)(uentry & ~1UL);
|
| 3290 | *pi = uentry & 1;
|
| 3291 |
|
| 3292 | return 0;
|
| 3293 | }
|
| 3294 |
|
| 3295 | |
| 3296 | * Walk curr->robust_list (very carefully, it's a userspace list!)
|
| 3297 | * and mark any locks found there dead, and notify any waiters.
|
| 3298 | *
|
| 3299 | * We silently return on any sign of list-walking problem.
|
| 3300 |
|
| 3301 | void exit_robust_list(struct task_struct *curr)
|
| 3302 | {
|
| 3303 | struct robust_list_head __user *head = curr->robust_list;
|
| 3304 | struct robust_list __user *entry, *next_entry, *pending;
|
| 3305 | unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
|
| 3306 | unsigned int uninitialized_var(next_pi);
|
| 3307 | unsigned long futex_offset;
|
| 3308 | int rc;
|
| 3309 |
|
| 3310 | if (!futex_cmpxchg_enabled)
|
| 3311 | return;
|
| 3312 |
|
| 3313 | |
| 3314 | * Fetch the list head (which was registered earlier, via
|
| 3315 | * sys_set_robust_list()):
|
| 3316 |
|
| 3317 | if (fetch_robust_entry(&entry, &head->list.next, &pi))
|
| 3318 | return;
|
| 3319 | |
| 3320 | * Fetch the relative futex offset:
|
| 3321 |
|
| 3322 | if (get_user(futex_offset, &head->futex_offset))
|
| 3323 | return;
|
| 3324 | |
| 3325 | * Fetch any possibly pending lock-add first, and handle it
|
| 3326 | * if it exists:
|
| 3327 |
|
| 3328 | if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
|
| 3329 | return;
|
| 3330 |
|
| 3331 | next_entry = NULL;
|
| 3332 | while (entry != &head->list) {
|
| 3333 | |
| 3334 | * Fetch the next entry in the list before calling
|
| 3335 | * handle_futex_death:
|
| 3336 |
|
| 3337 | rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
|
| 3338 | |
| 3339 | * A pending lock might already be on the list, so
|
| 3340 | * don't process it twice:
|
| 3341 |
|
| 3342 | if (entry != pending)
|
| 3343 | if (handle_futex_death((void __user *)entry + futex_offset,
|
| 3344 | curr, pi))
|
| 3345 | return;
|
| 3346 | if (rc)
|
| 3347 | return;
|
| 3348 | entry = next_entry;
|
| 3349 | pi = next_pi;
|
| 3350 | |
| 3351 | * Avoid excessively long or circular lists:
|
| 3352 |
|
| 3353 | if (!--limit)
|
| 3354 | break;
|
| 3355 |
|
| 3356 | cond_resched();
|
| 3357 | }
|
| 3358 |
|
| 3359 | if (pending)
|
| 3360 | handle_futex_death((void __user *)pending + futex_offset,
|
| 3361 | curr, pip);
|
| 3362 | }
|
| 3363 |
|
| 3364 | long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
|
| 3365 | u32 __user *uaddr2, u32 val2, u32 val3)
|
| 3366 | {
|
| 3367 | int cmd = op & FUTEX_CMD_MASK;
|
| 3368 | unsigned int flags = 0;
|
| 3369 |
|
| 3370 | if (!(op & FUTEX_PRIVATE_FLAG))
|
| 3371 | flags |= FLAGS_SHARED;
|
| 3372 |
|
| 3373 | if (op & FUTEX_CLOCK_REALTIME) {
|
| 3374 | flags |= FLAGS_CLOCKRT;
|
| 3375 | if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \
|
| 3376 | cmd != FUTEX_WAIT_REQUEUE_PI)
|
| 3377 | return -ENOSYS;
|
| 3378 | }
|
| 3379 |
|
| 3380 | switch (cmd) {
|
| 3381 | case FUTEX_LOCK_PI:
|
| 3382 | case FUTEX_UNLOCK_PI:
|
| 3383 | case FUTEX_TRYLOCK_PI:
|
| 3384 | case FUTEX_WAIT_REQUEUE_PI:
|
| 3385 | case FUTEX_CMP_REQUEUE_PI:
|
| 3386 | if (!futex_cmpxchg_enabled)
|
| 3387 | return -ENOSYS;
|
| 3388 | }
|
| 3389 |
|
| 3390 | switch (cmd) {
|
| 3391 | case FUTEX_WAIT:
|
| 3392 | val3 = FUTEX_BITSET_MATCH_ANY;
|
| 3393 | case FUTEX_WAIT_BITSET:
|
| 3394 | return futex_wait(uaddr, flags, val, timeout, val3);
|
| 3395 | case FUTEX_WAKE:
|
| 3396 | val3 = FUTEX_BITSET_MATCH_ANY;
|
| 3397 | case FUTEX_WAKE_BITSET:
|
| 3398 | return futex_wake(uaddr, flags, val, val3);
|
| 3399 | case FUTEX_REQUEUE:
|
| 3400 | return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
|
| 3401 | case FUTEX_CMP_REQUEUE:
|
| 3402 | return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
|
| 3403 | case FUTEX_WAKE_OP:
|
| 3404 | return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
|
| 3405 | case FUTEX_LOCK_PI:
|
| 3406 | return futex_lock_pi(uaddr, flags, timeout, 0);
|
| 3407 | case FUTEX_UNLOCK_PI:
|
| 3408 | return futex_unlock_pi(uaddr, flags);
|
| 3409 | case FUTEX_TRYLOCK_PI:
|
| 3410 | return futex_lock_pi(uaddr, flags, NULL, 1);
|
| 3411 | case FUTEX_WAIT_REQUEUE_PI:
|
| 3412 | val3 = FUTEX_BITSET_MATCH_ANY;
|
| 3413 | return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
|
| 3414 | uaddr2);
|
| 3415 | case FUTEX_CMP_REQUEUE_PI:
|
| 3416 | return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
|
| 3417 | }
|
| 3418 | return -ENOSYS;
|
| 3419 | }
|
| 3420 |
|
| 3421 |
|
| 3422 | SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
|
| 3423 | struct timespec __user *, utime, u32 __user *, uaddr2,
|
| 3424 | u32, val3)
|
| 3425 | {
|
| 3426 | struct timespec ts;
|
| 3427 | ktime_t t, *tp = NULL;
|
| 3428 | u32 val2 = 0;
|
| 3429 | int cmd = op & FUTEX_CMD_MASK;
|
| 3430 |
|
| 3431 | if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
|
| 3432 | cmd == FUTEX_WAIT_BITSET ||
|
| 3433 | cmd == FUTEX_WAIT_REQUEUE_PI)) {
|
| 3434 | if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
|
| 3435 | return -EFAULT;
|
| 3436 | if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
|
| 3437 | return -EFAULT;
|
| 3438 | if (!timespec_valid(&ts))
|
| 3439 | return -EINVAL;
|
| 3440 |
|
| 3441 | t = timespec_to_ktime(ts);
|
| 3442 | if (cmd == FUTEX_WAIT)
|
| 3443 | t = ktime_add_safe(ktime_get(), t);
|
| 3444 | tp = &t;
|
| 3445 | }
|
| 3446 | |
| 3447 | * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
|
| 3448 | * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
|
| 3449 |
|
| 3450 | if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
|
| 3451 | cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
|
| 3452 | val2 = (u32) (unsigned long) utime;
|
| 3453 |
|
| 3454 | return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
|
| 3455 | }
|
| 3456 |
|
| 3457 | static void __init futex_detect_cmpxchg(void)
|
| 3458 | {
|
| 3459 | #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
|
| 3460 | u32 curval;
|
| 3461 |
|
| 3462 | |
| 3463 | * This will fail and we want it. Some arch implementations do
|
| 3464 | * runtime detection of the futex_atomic_cmpxchg_inatomic()
|
| 3465 | * functionality. We want to know that before we call in any
|
| 3466 | * of the complex code paths. Also we want to prevent
|
| 3467 | * registration of robust lists in that case. NULL is
|
| 3468 | * guaranteed to fault and we get -EFAULT on functional
|
| 3469 | * implementation, the non-functional ones will return
|
| 3470 | * -ENOSYS.
|
| 3471 |
|
| 3472 | if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
|
| 3473 | futex_cmpxchg_enabled = 1;
|
| 3474 | #endif
|
| 3475 | }
|
| 3476 |
|
| 3477 | static int __init futex_init(void)
|
| 3478 | {
|
| 3479 | unsigned int futex_shift;
|
| 3480 | unsigned long i;
|
| 3481 |
|
| 3482 | #if CONFIG_BASE_SMALL
|
| 3483 | futex_hashsize = 16;
|
| 3484 | #else
|
| 3485 | futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
|
| 3486 | #endif
|
| 3487 |
|
| 3488 | futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
|
| 3489 | futex_hashsize, 0,
|
| 3490 | futex_hashsize < 256 ? HASH_SMALL : 0,
|
| 3491 | &futex_shift, NULL,
|
| 3492 | futex_hashsize, futex_hashsize);
|
| 3493 | futex_hashsize = 1UL << futex_shift;
|
| 3494 |
|
| 3495 | futex_detect_cmpxchg();
|
| 3496 |
|
| 3497 | for (i = 0; i < futex_hashsize; i++) {
|
| 3498 | atomic_set(&futex_queues[i].waiters, 0);
|
| 3499 | plist_head_init(&futex_queues[i].chain);
|
| 3500 | spin_lock_init(&futex_queues[i].lock);
|
| 3501 | }
|
| 3502 |
|
| 3503 | return 0;
|
| 3504 | }
|
| 3505 | core_initcall(futex_init);
|