| 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/hugetlb.h>
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| 65 | #include <linux/freezer.h>
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| 66 | #include <linux/bootmem.h>
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| 67 |
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| 68 | #include <asm/futex.h>
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| 69 |
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| 70 | #include "locking/rtmutex_common.h"
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| 71 |
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| 72 | |
| 73 | * READ this before attempting to hack on futexes!
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| 74 | *
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| 75 | * Basic futex operation and ordering guarantees
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| 76 | * =============================================
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| 77 | *
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| 78 | * The waiter reads the futex value in user space and calls
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| 79 | * futex_wait(). This function computes the hash bucket and acquires
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| 80 | * the hash bucket lock. After that it reads the futex user space value
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| 81 | * again and verifies that the data has not changed. If it has not changed
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| 82 | * it enqueues itself into the hash bucket, releases the hash bucket lock
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| 83 | * and schedules.
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| 84 | *
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| 85 | * The waker side modifies the user space value of the futex and calls
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| 86 | * futex_wake(). This function computes the hash bucket and acquires the
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| 87 | * hash bucket lock. Then it looks for waiters on that futex in the hash
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| 88 | * bucket and wakes them.
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| 89 | *
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| 90 | * In futex wake up scenarios where no tasks are blocked on a futex, taking
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| 91 | * the hb spinlock can be avoided and simply return. In order for this
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| 92 | * optimization to work, ordering guarantees must exist so that the waiter
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| 93 | * being added to the list is acknowledged when the list is concurrently being
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| 94 | * checked by the waker, avoiding scenarios like the following:
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| 95 | *
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| 96 | * CPU 0 CPU 1
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| 97 | * val = *futex;
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| 98 | * sys_futex(WAIT, futex, val);
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| 99 | * futex_wait(futex, val);
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| 100 | * uval = *futex;
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| 101 | * *futex = newval;
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| 102 | * sys_futex(WAKE, futex);
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| 103 | * futex_wake(futex);
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| 104 | * if (queue_empty())
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| 105 | * return;
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| 106 | * if (uval == val)
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| 107 | * lock(hash_bucket(futex));
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| 108 | * queue();
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| 109 | * unlock(hash_bucket(futex));
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| 110 | * schedule();
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| 111 | *
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| 112 | * This would cause the waiter on CPU 0 to wait forever because it
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| 113 | * missed the transition of the user space value from val to newval
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| 114 | * and the waker did not find the waiter in the hash bucket queue.
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| 115 | *
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| 116 | * The correct serialization ensures that a waiter either observes
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| 117 | * the changed user space value before blocking or is woken by a
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| 118 | * concurrent waker:
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| 119 | *
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| 120 | * CPU 0 CPU 1
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| 121 | * val = *futex;
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| 122 | * sys_futex(WAIT, futex, val);
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| 123 | * futex_wait(futex, val);
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| 124 | *
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| 125 | * waiters++; (a)
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| 126 | * mb(); (A) <-- paired with -.
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| 127 | * |
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| 128 | * lock(hash_bucket(futex)); |
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| 129 | * |
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| 130 | * uval = *futex; |
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| 131 | * | *futex = newval;
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| 132 | * | sys_futex(WAKE, futex);
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| 133 | * | futex_wake(futex);
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| 134 | * |
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| 135 | * `-------> mb(); (B)
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| 136 | * if (uval == val)
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| 137 | * queue();
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| 138 | * unlock(hash_bucket(futex));
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| 139 | * schedule(); if (waiters)
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| 140 | * lock(hash_bucket(futex));
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| 141 | * else wake_waiters(futex);
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| 142 | * waiters--; (b) unlock(hash_bucket(futex));
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| 143 | *
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| 144 | * Where (A) orders the waiters increment and the futex value read through
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| 145 | * atomic operations (see hb_waiters_inc) and where (B) orders the write
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| 146 | * to futex and the waiters read -- this is done by the barriers in
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| 147 | * get_futex_key_refs(), through either ihold or atomic_inc, depending on the
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| 148 | * futex type.
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| 149 | *
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| 150 | * This yields the following case (where X:=waiters, Y:=futex):
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| 151 | *
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| 152 | * X = Y = 0
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| 153 | *
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| 154 | * w[X]=1 w[Y]=1
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| 155 | * MB MB
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| 156 | * r[Y]=y r[X]=x
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| 157 | *
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| 158 | * Which guarantees that x==0 && y==0 is impossible; which translates back into
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| 159 | * the guarantee that we cannot both miss the futex variable change and the
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| 160 | * enqueue.
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| 161 | *
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| 162 | * Note that a new waiter is accounted for in (a) even when it is possible that
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| 163 | * the wait call can return error, in which case we backtrack from it in (b).
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| 164 | * Refer to the comment in queue_lock().
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| 165 | *
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| 166 | * Similarly, in order to account for waiters being requeued on another
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| 167 | * address we always increment the waiters for the destination bucket before
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| 168 | * acquiring the lock. It then decrements them again after releasing it -
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| 169 | * the code that actually moves the futex(es) between hash buckets (requeue_futex)
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| 170 | * will do the additional required waiter count housekeeping. This is done for
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| 171 | * double_lock_hb() and double_unlock_hb(), respectively.
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| 172 |
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| 173 |
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| 174 | #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
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| 175 | int __read_mostly futex_cmpxchg_enabled;
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| 176 | #endif
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| 177 |
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| 178 | |
| 179 | * Futex flags used to encode options to functions and preserve them across
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| 180 | * restarts.
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| 181 |
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| 182 | #define FLAGS_SHARED 0x01
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| 183 | #define FLAGS_CLOCKRT 0x02
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| 184 | #define FLAGS_HAS_TIMEOUT 0x04
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| 185 |
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| 186 | |
| 187 | * Priority Inheritance state:
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| 188 |
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| 189 | struct futex_pi_state {
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| 190 | |
| 191 | * list of 'owned' pi_state instances - these have to be
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| 192 | * cleaned up in do_exit() if the task exits prematurely:
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| 193 |
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| 194 | struct list_head list;
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| 195 |
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| 196 | |
| 197 | * The PI object:
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| 198 |
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| 199 | struct rt_mutex pi_mutex;
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| 200 |
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| 201 | struct task_struct *owner;
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| 202 | atomic_t refcount;
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| 203 |
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| 204 | union futex_key key;
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| 205 | };
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| 206 |
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| 207 | |
| 208 | * struct futex_q - The hashed futex queue entry, one per waiting task
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| 209 | * @list: priority-sorted list of tasks waiting on this futex
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| 210 | * @task: the task waiting on the futex
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| 211 | * @lock_ptr: the hash bucket lock
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| 212 | * @key: the key the futex is hashed on
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| 213 | * @pi_state: optional priority inheritance state
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| 214 | * @rt_waiter: rt_waiter storage for use with requeue_pi
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| 215 | * @requeue_pi_key: the requeue_pi target futex key
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| 216 | * @bitset: bitset for the optional bitmasked wakeup
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| 217 | *
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| 218 | * We use this hashed waitqueue, instead of a normal wait_queue_t, so
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| 219 | * we can wake only the relevant ones (hashed queues may be shared).
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| 220 | *
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| 221 | * A futex_q has a woken state, just like tasks have TASK_RUNNING.
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| 222 | * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
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| 223 | * The order of wakeup is always to make the first condition true, then
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| 224 | * the second.
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| 225 | *
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| 226 | * PI futexes are typically woken before they are removed from the hash list via
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| 227 | * the rt_mutex code. See unqueue_me_pi().
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| 228 |
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| 229 | struct futex_q {
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| 230 | struct plist_node list;
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| 231 |
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| 232 | struct task_struct *task;
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| 233 | spinlock_t *lock_ptr;
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| 234 | union futex_key key;
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| 235 | struct futex_pi_state *pi_state;
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| 236 | struct rt_mutex_waiter *rt_waiter;
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| 237 | union futex_key *requeue_pi_key;
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| 238 | u32 bitset;
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| 239 | };
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| 240 |
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| 241 | static const struct futex_q futex_q_init = {
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| 242 |
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| 243 | .key = FUTEX_KEY_INIT,
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| 244 | .bitset = FUTEX_BITSET_MATCH_ANY
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| 245 | };
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| 246 |
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| 247 | |
| 248 | * Hash buckets are shared by all the futex_keys that hash to the same
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| 249 | * location. Each key may have multiple futex_q structures, one for each task
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| 250 | * waiting on a futex.
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| 251 |
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| 252 | struct futex_hash_bucket {
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| 253 | atomic_t waiters;
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| 254 | spinlock_t lock;
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| 255 | struct plist_head chain;
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| 256 | } ____cacheline_aligned_in_smp;
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| 257 |
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| 258 | static unsigned long __read_mostly futex_hashsize;
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| 259 |
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| 260 | static struct futex_hash_bucket *futex_queues;
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| 261 |
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| 262 | static inline void futex_get_mm(union futex_key *key)
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| 263 | {
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| 264 | atomic_inc(&key->private.mm->mm_count);
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| 265 | |
| 266 | * Ensure futex_get_mm() implies a full barrier such that
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| 267 | * get_futex_key() implies a full barrier. This is relied upon
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| 268 | * as full barrier (B), see the ordering comment above.
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| 269 |
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| 270 | smp_mb__after_atomic_inc();
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| 271 | }
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| 272 |
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| 273 | |
| 274 | * Reflects a new waiter being added to the waitqueue.
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| 275 |
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| 276 | static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
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| 277 | {
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| 278 | #ifdef CONFIG_SMP
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| 279 | atomic_inc(&hb->waiters);
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| 280 | |
| 281 | * Full barrier (A), see the ordering comment above.
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| 282 |
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| 283 | smp_mb__after_atomic_inc();
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| 284 | #endif
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| 285 | }
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| 286 |
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| 287 | |
| 288 | * Reflects a waiter being removed from the waitqueue by wakeup
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| 289 | * paths.
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| 290 |
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| 291 | static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
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| 292 | {
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| 293 | #ifdef CONFIG_SMP
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| 294 | atomic_dec(&hb->waiters);
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| 295 | #endif
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| 296 | }
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| 297 |
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| 298 | static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
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| 299 | {
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| 300 | #ifdef CONFIG_SMP
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| 301 | return atomic_read(&hb->waiters);
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| 302 | #else
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| 303 | return 1;
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| 304 | #endif
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| 305 | }
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| 306 |
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| 307 | |
| 308 | * We hash on the keys returned from get_futex_key (see below).
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| 309 |
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| 310 | static struct futex_hash_bucket *hash_futex(union futex_key *key)
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| 311 | {
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| 312 | u32 hash = jhash2((u32*)&key->both.word,
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| 313 | (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
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| 314 | key->both.offset);
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| 315 | return &futex_queues[hash & (futex_hashsize - 1)];
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| 316 | }
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| 317 |
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| 318 | |
| 319 | * Return 1 if two futex_keys are equal, 0 otherwise.
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| 320 |
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| 321 | static inline int match_futex(union futex_key *key1, union futex_key *key2)
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| 322 | {
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| 323 | return (key1 && key2
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| 324 | && key1->both.word == key2->both.word
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| 325 | && key1->both.ptr == key2->both.ptr
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| 326 | && key1->both.offset == key2->both.offset);
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| 327 | }
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| 328 |
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| 329 | |
| 330 | * Take a reference to the resource addressed by a key.
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| 331 | * Can be called while holding spinlocks.
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| 332 | *
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| 333 |
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| 334 | static void get_futex_key_refs(union futex_key *key)
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| 335 | {
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| 336 | if (!key->both.ptr)
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| 337 | return;
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| 338 |
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| 339 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
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| 340 | case FUT_OFF_INODE:
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| 341 | ihold(key->shared.inode);
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| 342 | break;
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| 343 | case FUT_OFF_MMSHARED:
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| 344 | futex_get_mm(key);
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| 345 | break;
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| 346 | }
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| 347 | }
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| 348 |
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| 349 | |
| 350 | * Drop a reference to the resource addressed by a key.
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| 351 | * The hash bucket spinlock must not be held.
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| 352 |
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| 353 | static void drop_futex_key_refs(union futex_key *key)
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| 354 | {
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| 355 | if (!key->both.ptr) {
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| 356 |
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| 357 | WARN_ON_ONCE(1);
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| 358 | return;
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| 359 | }
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| 360 |
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| 361 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
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| 362 | case FUT_OFF_INODE:
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| 363 | iput(key->shared.inode);
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| 364 | break;
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| 365 | case FUT_OFF_MMSHARED:
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| 366 | mmdrop(key->private.mm);
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| 367 | break;
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| 368 | }
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| 369 | }
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| 370 |
|
| 371 | |
| 372 | * get_futex_key() - Get parameters which are the keys for a futex
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| 373 | * @uaddr: virtual address of the futex
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| 374 | * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
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| 375 | * @key: address where result is stored.
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| 376 | * @rw: mapping needs to be read/write (values: VERIFY_READ,
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| 377 | * VERIFY_WRITE)
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| 378 | *
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| 379 | * Return: a negative error code or 0
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| 380 | *
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| 381 | * The key words are stored in *key on success.
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| 382 | *
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| 383 | * For shared mappings, it's (page->index, file_inode(vma->vm_file),
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| 384 | * offset_within_page). For private mappings, it's (uaddr, current->mm).
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| 385 | * We can usually work out the index without swapping in the page.
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| 386 | *
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| 387 | * lock_page() might sleep, the caller should not hold a spinlock.
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| 388 |
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| 389 | static int
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| 390 | get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
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| 391 | {
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| 392 | unsigned long address = (unsigned long)uaddr;
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| 393 | struct mm_struct *mm = current->mm;
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| 394 | struct page *page, *page_head;
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| 395 | int err, ro = 0;
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| 396 |
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| 397 | |
| 398 | * The futex address must be "naturally" aligned.
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| 399 |
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| 400 | key->both.offset = address % PAGE_SIZE;
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| 401 | if (unlikely((address % sizeof(u32)) != 0))
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| 402 | return -EINVAL;
|
| 403 | address -= key->both.offset;
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| 404 |
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| 405 | if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
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| 406 | return -EFAULT;
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| 407 |
|
| 408 | |
| 409 | * PROCESS_PRIVATE futexes are fast.
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| 410 | * As the mm cannot disappear under us and the 'key' only needs
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| 411 | * virtual address, we dont even have to find the underlying vma.
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| 412 | * Note : We do have to check 'uaddr' is a valid user address,
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| 413 | * but access_ok() should be faster than find_vma()
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| 414 |
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| 415 | if (!fshared) {
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| 416 | key->private.mm = mm;
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| 417 | key->private.address = address;
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| 418 | get_futex_key_refs(key);
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| 419 | return 0;
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| 420 | }
|
| 421 |
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| 422 | again:
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| 423 | err = get_user_pages_fast(address, 1, 1, &page);
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| 424 | |
| 425 | * If write access is not required (eg. FUTEX_WAIT), try
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| 426 | * and get read-only access.
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| 427 |
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| 428 | if (err == -EFAULT && rw == VERIFY_READ) {
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| 429 | err = get_user_pages_fast(address, 1, 0, &page);
|
| 430 | ro = 1;
|
| 431 | }
|
| 432 | if (err < 0)
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| 433 | return err;
|
| 434 | else
|
| 435 | err = 0;
|
| 436 |
|
| 437 | #ifdef CONFIG_TRANSPARENT_HUGEPAGE
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| 438 | page_head = page;
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| 439 | if (unlikely(PageTail(page))) {
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| 440 | put_page(page);
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| 441 |
|
| 442 | local_irq_disable();
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| 443 | if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) {
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| 444 | page_head = compound_head(page);
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| 445 | |
| 446 | * page_head is valid pointer but we must pin
|
| 447 | * it before taking the PG_lock and/or
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| 448 | * PG_compound_lock. The moment we re-enable
|
| 449 | * irqs __split_huge_page_splitting() can
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| 450 | * return and the head page can be freed from
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| 451 | * under us. We can't take the PG_lock and/or
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| 452 | * PG_compound_lock on a page that could be
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| 453 | * freed from under us.
|
| 454 |
|
| 455 | if (page != page_head) {
|
| 456 | get_page(page_head);
|
| 457 | put_page(page);
|
| 458 | }
|
| 459 | local_irq_enable();
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| 460 | } else {
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| 461 | local_irq_enable();
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| 462 | goto again;
|
| 463 | }
|
| 464 | }
|
| 465 | #else
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| 466 | page_head = compound_head(page);
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| 467 | if (page != page_head) {
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| 468 | get_page(page_head);
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| 469 | put_page(page);
|
| 470 | }
|
| 471 | #endif
|
| 472 |
|
| 473 | lock_page(page_head);
|
| 474 |
|
| 475 | |
| 476 | * If page_head->mapping is NULL, then it cannot be a PageAnon
|
| 477 | * page; but it might be the ZERO_PAGE or in the gate area or
|
| 478 | * in a special mapping (all cases which we are happy to fail);
|
| 479 | * or it may have been a good file page when get_user_pages_fast
|
| 480 | * found it, but truncated or holepunched or subjected to
|
| 481 | * invalidate_complete_page2 before we got the page lock (also
|
| 482 | * cases which we are happy to fail). And we hold a reference,
|
| 483 | * so refcount care in invalidate_complete_page's remove_mapping
|
| 484 | * prevents drop_caches from setting mapping to NULL beneath us.
|
| 485 | *
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| 486 | * The case we do have to guard against is when memory pressure made
|
| 487 | * shmem_writepage move it from filecache to swapcache beneath us:
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| 488 | * an unlikely race, but we do need to retry for page_head->mapping.
|
| 489 |
|
| 490 | if (!page_head->mapping) {
|
| 491 | int shmem_swizzled = PageSwapCache(page_head);
|
| 492 | unlock_page(page_head);
|
| 493 | put_page(page_head);
|
| 494 | if (shmem_swizzled)
|
| 495 | goto again;
|
| 496 | return -EFAULT;
|
| 497 | }
|
| 498 |
|
| 499 | |
| 500 | * Private mappings are handled in a simple way.
|
| 501 | *
|
| 502 | * NOTE: When userspace waits on a MAP_SHARED mapping, even if
|
| 503 | * it's a read-only handle, it's expected that futexes attach to
|
| 504 | * the object not the particular process.
|
| 505 |
|
| 506 | if (PageAnon(page_head)) {
|
| 507 | |
| 508 | * A RO anonymous page will never change and thus doesn't make
|
| 509 | * sense for futex operations.
|
| 510 |
|
| 511 | if (ro) {
|
| 512 | err = -EFAULT;
|
| 513 | goto out;
|
| 514 | }
|
| 515 |
|
| 516 | key->both.offset |= FUT_OFF_MMSHARED;
|
| 517 | key->private.mm = mm;
|
| 518 | key->private.address = address;
|
| 519 | } else {
|
| 520 | key->both.offset |= FUT_OFF_INODE;
|
| 521 | key->shared.inode = page_head->mapping->host;
|
| 522 | key->shared.pgoff = basepage_index(page);
|
| 523 | }
|
| 524 |
|
| 525 | get_futex_key_refs(key);
|
| 526 |
|
| 527 | out:
|
| 528 | unlock_page(page_head);
|
| 529 | put_page(page_head);
|
| 530 | return err;
|
| 531 | }
|
| 532 |
|
| 533 | static inline void put_futex_key(union futex_key *key)
|
| 534 | {
|
| 535 | drop_futex_key_refs(key);
|
| 536 | }
|
| 537 |
|
| 538 | |
| 539 | * fault_in_user_writeable() - Fault in user address and verify RW access
|
| 540 | * @uaddr: pointer to faulting user space address
|
| 541 | *
|
| 542 | * Slow path to fixup the fault we just took in the atomic write
|
| 543 | * access to @uaddr.
|
| 544 | *
|
| 545 | * We have no generic implementation of a non-destructive write to the
|
| 546 | * user address. We know that we faulted in the atomic pagefault
|
| 547 | * disabled section so we can as well avoid the #PF overhead by
|
| 548 | * calling get_user_pages() right away.
|
| 549 |
|
| 550 | static int fault_in_user_writeable(u32 __user *uaddr)
|
| 551 | {
|
| 552 | struct mm_struct *mm = current->mm;
|
| 553 | int ret;
|
| 554 |
|
| 555 | down_read(&mm->mmap_sem);
|
| 556 | ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
|
| 557 | FAULT_FLAG_WRITE);
|
| 558 | up_read(&mm->mmap_sem);
|
| 559 |
|
| 560 | return ret < 0 ? ret : 0;
|
| 561 | }
|
| 562 |
|
| 563 | |
| 564 | * futex_top_waiter() - Return the highest priority waiter on a futex
|
| 565 | * @hb: the hash bucket the futex_q's reside in
|
| 566 | * @key: the futex key (to distinguish it from other futex futex_q's)
|
| 567 | *
|
| 568 | * Must be called with the hb lock held.
|
| 569 |
|
| 570 | static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
|
| 571 | union futex_key *key)
|
| 572 | {
|
| 573 | struct futex_q *this;
|
| 574 |
|
| 575 | plist_for_each_entry(this, &hb->chain, list) {
|
| 576 | if (match_futex(&this->key, key))
|
| 577 | return this;
|
| 578 | }
|
| 579 | return NULL;
|
| 580 | }
|
| 581 |
|
| 582 | static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
|
| 583 | u32 uval, u32 newval)
|
| 584 | {
|
| 585 | int ret;
|
| 586 |
|
| 587 | pagefault_disable();
|
| 588 | ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
|
| 589 | pagefault_enable();
|
| 590 |
|
| 591 | return ret;
|
| 592 | }
|
| 593 |
|
| 594 | static int get_futex_value_locked(u32 *dest, u32 __user *from)
|
| 595 | {
|
| 596 | int ret;
|
| 597 |
|
| 598 | pagefault_disable();
|
| 599 | ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
|
| 600 | pagefault_enable();
|
| 601 |
|
| 602 | return ret ? -EFAULT : 0;
|
| 603 | }
|
| 604 |
|
| 605 |
|
| 606 | |
| 607 | * PI code:
|
| 608 |
|
| 609 | static int refill_pi_state_cache(void)
|
| 610 | {
|
| 611 | struct futex_pi_state *pi_state;
|
| 612 |
|
| 613 | if (likely(current->pi_state_cache))
|
| 614 | return 0;
|
| 615 |
|
| 616 | pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
|
| 617 |
|
| 618 | if (!pi_state)
|
| 619 | return -ENOMEM;
|
| 620 |
|
| 621 | INIT_LIST_HEAD(&pi_state->list);
|
| 622 |
|
| 623 | pi_state->owner = NULL;
|
| 624 | atomic_set(&pi_state->refcount, 1);
|
| 625 | pi_state->key = FUTEX_KEY_INIT;
|
| 626 |
|
| 627 | current->pi_state_cache = pi_state;
|
| 628 |
|
| 629 | return 0;
|
| 630 | }
|
| 631 |
|
| 632 | static struct futex_pi_state * alloc_pi_state(void)
|
| 633 | {
|
| 634 | struct futex_pi_state *pi_state = current->pi_state_cache;
|
| 635 |
|
| 636 | WARN_ON(!pi_state);
|
| 637 | current->pi_state_cache = NULL;
|
| 638 |
|
| 639 | return pi_state;
|
| 640 | }
|
| 641 |
|
| 642 | static void free_pi_state(struct futex_pi_state *pi_state)
|
| 643 | {
|
| 644 | if (!atomic_dec_and_test(&pi_state->refcount))
|
| 645 | return;
|
| 646 |
|
| 647 | |
| 648 | * If pi_state->owner is NULL, the owner is most probably dying
|
| 649 | * and has cleaned up the pi_state already
|
| 650 |
|
| 651 | if (pi_state->owner) {
|
| 652 | raw_spin_lock_irq(&pi_state->owner->pi_lock);
|
| 653 | list_del_init(&pi_state->list);
|
| 654 | raw_spin_unlock_irq(&pi_state->owner->pi_lock);
|
| 655 |
|
| 656 | rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
|
| 657 | }
|
| 658 |
|
| 659 | if (current->pi_state_cache)
|
| 660 | kfree(pi_state);
|
| 661 | else {
|
| 662 | |
| 663 | * pi_state->list is already empty.
|
| 664 | * clear pi_state->owner.
|
| 665 | * refcount is at 0 - put it back to 1.
|
| 666 |
|
| 667 | pi_state->owner = NULL;
|
| 668 | atomic_set(&pi_state->refcount, 1);
|
| 669 | current->pi_state_cache = pi_state;
|
| 670 | }
|
| 671 | }
|
| 672 |
|
| 673 | |
| 674 | * Look up the task based on what TID userspace gave us.
|
| 675 | * We dont trust it.
|
| 676 |
|
| 677 | static struct task_struct * futex_find_get_task(pid_t pid)
|
| 678 | {
|
| 679 | struct task_struct *p;
|
| 680 |
|
| 681 | rcu_read_lock();
|
| 682 | p = find_task_by_vpid(pid);
|
| 683 | if (p)
|
| 684 | get_task_struct(p);
|
| 685 |
|
| 686 | rcu_read_unlock();
|
| 687 |
|
| 688 | return p;
|
| 689 | }
|
| 690 |
|
| 691 | |
| 692 | * This task is holding PI mutexes at exit time => bad.
|
| 693 | * Kernel cleans up PI-state, but userspace is likely hosed.
|
| 694 | * (Robust-futex cleanup is separate and might save the day for userspace.)
|
| 695 |
|
| 696 | void exit_pi_state_list(struct task_struct *curr)
|
| 697 | {
|
| 698 | struct list_head *next, *head = &curr->pi_state_list;
|
| 699 | struct futex_pi_state *pi_state;
|
| 700 | struct futex_hash_bucket *hb;
|
| 701 | union futex_key key = FUTEX_KEY_INIT;
|
| 702 |
|
| 703 | if (!futex_cmpxchg_enabled)
|
| 704 | return;
|
| 705 | |
| 706 | * We are a ZOMBIE and nobody can enqueue itself on
|
| 707 | * pi_state_list anymore, but we have to be careful
|
| 708 | * versus waiters unqueueing themselves:
|
| 709 |
|
| 710 | raw_spin_lock_irq(&curr->pi_lock);
|
| 711 | while (!list_empty(head)) {
|
| 712 |
|
| 713 | next = head->next;
|
| 714 | pi_state = list_entry(next, struct futex_pi_state, list);
|
| 715 | key = pi_state->key;
|
| 716 | hb = hash_futex(&key);
|
| 717 | raw_spin_unlock_irq(&curr->pi_lock);
|
| 718 |
|
| 719 | spin_lock(&hb->lock);
|
| 720 |
|
| 721 | raw_spin_lock_irq(&curr->pi_lock);
|
| 722 | |
| 723 | * We dropped the pi-lock, so re-check whether this
|
| 724 | * task still owns the PI-state:
|
| 725 |
|
| 726 | if (head->next != next) {
|
| 727 | spin_unlock(&hb->lock);
|
| 728 | continue;
|
| 729 | }
|
| 730 |
|
| 731 | WARN_ON(pi_state->owner != curr);
|
| 732 | WARN_ON(list_empty(&pi_state->list));
|
| 733 | list_del_init(&pi_state->list);
|
| 734 | pi_state->owner = NULL;
|
| 735 | raw_spin_unlock_irq(&curr->pi_lock);
|
| 736 |
|
| 737 | rt_mutex_unlock(&pi_state->pi_mutex);
|
| 738 |
|
| 739 | spin_unlock(&hb->lock);
|
| 740 |
|
| 741 | raw_spin_lock_irq(&curr->pi_lock);
|
| 742 | }
|
| 743 | raw_spin_unlock_irq(&curr->pi_lock);
|
| 744 | }
|
| 745 |
|
| 746 | |
| 747 | * We need to check the following states:
|
| 748 | *
|
| 749 | * Waiter | pi_state | pi->owner | uTID | uODIED | ?
|
| 750 | *
|
| 751 | * [1] NULL | --- | --- | 0 | 0/1 | Valid
|
| 752 | * [2] NULL | --- | --- | >0 | 0/1 | Valid
|
| 753 | *
|
| 754 | * [3] Found | NULL | -- | Any | 0/1 | Invalid
|
| 755 | *
|
| 756 | * [4] Found | Found | NULL | 0 | 1 | Valid
|
| 757 | * [5] Found | Found | NULL | >0 | 1 | Invalid
|
| 758 | *
|
| 759 | * [6] Found | Found | task | 0 | 1 | Valid
|
| 760 | *
|
| 761 | * [7] Found | Found | NULL | Any | 0 | Invalid
|
| 762 | *
|
| 763 | * [8] Found | Found | task | ==taskTID | 0/1 | Valid
|
| 764 | * [9] Found | Found | task | 0 | 0 | Invalid
|
| 765 | * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
|
| 766 | *
|
| 767 | * [1] Indicates that the kernel can acquire the futex atomically. We
|
| 768 | * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
|
| 769 | *
|
| 770 | * [2] Valid, if TID does not belong to a kernel thread. If no matching
|
| 771 | * thread is found then it indicates that the owner TID has died.
|
| 772 | *
|
| 773 | * [3] Invalid. The waiter is queued on a non PI futex
|
| 774 | *
|
| 775 | * [4] Valid state after exit_robust_list(), which sets the user space
|
| 776 | * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
|
| 777 | *
|
| 778 | * [5] The user space value got manipulated between exit_robust_list()
|
| 779 | * and exit_pi_state_list()
|
| 780 | *
|
| 781 | * [6] Valid state after exit_pi_state_list() which sets the new owner in
|
| 782 | * the pi_state but cannot access the user space value.
|
| 783 | *
|
| 784 | * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
|
| 785 | *
|
| 786 | * [8] Owner and user space value match
|
| 787 | *
|
| 788 | * [9] There is no transient state which sets the user space TID to 0
|
| 789 | * except exit_robust_list(), but this is indicated by the
|
| 790 | * FUTEX_OWNER_DIED bit. See [4]
|
| 791 | *
|
| 792 | * [10] There is no transient state which leaves owner and user space
|
| 793 | * TID out of sync.
|
| 794 |
|
| 795 | static int
|
| 796 | lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
|
| 797 | union futex_key *key, struct futex_pi_state **ps)
|
| 798 | {
|
| 799 | struct futex_pi_state *pi_state = NULL;
|
| 800 | struct futex_q *this, *next;
|
| 801 | struct task_struct *p;
|
| 802 | pid_t pid = uval & FUTEX_TID_MASK;
|
| 803 |
|
| 804 | plist_for_each_entry_safe(this, next, &hb->chain, list) {
|
| 805 | if (match_futex(&this->key, key)) {
|
| 806 | |
| 807 | * Sanity check the waiter before increasing
|
| 808 | * the refcount and attaching to it.
|
| 809 |
|
| 810 | pi_state = this->pi_state;
|
| 811 | |
| 812 | * Userspace might have messed up non-PI and
|
| 813 | * PI futexes [3]
|
| 814 |
|
| 815 | if (unlikely(!pi_state))
|
| 816 | return -EINVAL;
|
| 817 |
|
| 818 | WARN_ON(!atomic_read(&pi_state->refcount));
|
| 819 |
|
| 820 | |
| 821 | * Handle the owner died case:
|
| 822 |
|
| 823 | if (uval & FUTEX_OWNER_DIED) {
|
| 824 | |
| 825 | * exit_pi_state_list sets owner to NULL and
|
| 826 | * wakes the topmost waiter. The task which
|
| 827 | * acquires the pi_state->rt_mutex will fixup
|
| 828 | * owner.
|
| 829 |
|
| 830 | if (!pi_state->owner) {
|
| 831 | |
| 832 | * No pi state owner, but the user
|
| 833 | * space TID is not 0. Inconsistent
|
| 834 | * state. [5]
|
| 835 |
|
| 836 | if (pid)
|
| 837 | return -EINVAL;
|
| 838 | |
| 839 | * Take a ref on the state and
|
| 840 | * return. [4]
|
| 841 |
|
| 842 | goto out_state;
|
| 843 | }
|
| 844 |
|
| 845 | |
| 846 | * If TID is 0, then either the dying owner
|
| 847 | * has not yet executed exit_pi_state_list()
|
| 848 | * or some waiter acquired the rtmutex in the
|
| 849 | * pi state, but did not yet fixup the TID in
|
| 850 | * user space.
|
| 851 | *
|
| 852 | * Take a ref on the state and return. [6]
|
| 853 |
|
| 854 | if (!pid)
|
| 855 | goto out_state;
|
| 856 | } else {
|
| 857 | |
| 858 | * If the owner died bit is not set,
|
| 859 | * then the pi_state must have an
|
| 860 | * owner. [7]
|
| 861 |
|
| 862 | if (!pi_state->owner)
|
| 863 | return -EINVAL;
|
| 864 | }
|
| 865 |
|
| 866 | |
| 867 | * Bail out if user space manipulated the
|
| 868 | * futex value. If pi state exists then the
|
| 869 | * owner TID must be the same as the user
|
| 870 | * space TID. [9/10]
|
| 871 |
|
| 872 | if (pid != task_pid_vnr(pi_state->owner))
|
| 873 | return -EINVAL;
|
| 874 |
|
| 875 | out_state:
|
| 876 | atomic_inc(&pi_state->refcount);
|
| 877 | *ps = pi_state;
|
| 878 | return 0;
|
| 879 | }
|
| 880 | }
|
| 881 |
|
| 882 | |
| 883 | * We are the first waiter - try to look up the real owner and attach
|
| 884 | * the new pi_state to it, but bail out when TID = 0 [1]
|
| 885 |
|
| 886 | if (!pid)
|
| 887 | return -ESRCH;
|
| 888 | p = futex_find_get_task(pid);
|
| 889 | if (!p)
|
| 890 | return -ESRCH;
|
| 891 |
|
| 892 | if (!p->mm) {
|
| 893 | put_task_struct(p);
|
| 894 | return -EPERM;
|
| 895 | }
|
| 896 |
|
| 897 | |
| 898 | * We need to look at the task state flags to figure out,
|
| 899 | * whether the task is exiting. To protect against the do_exit
|
| 900 | * change of the task flags, we do this protected by
|
| 901 | * p->pi_lock:
|
| 902 |
|
| 903 | raw_spin_lock_irq(&p->pi_lock);
|
| 904 | if (unlikely(p->flags & PF_EXITING)) {
|
| 905 | |
| 906 | * The task is on the way out. When PF_EXITPIDONE is
|
| 907 | * set, we know that the task has finished the
|
| 908 | * cleanup:
|
| 909 |
|
| 910 | int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
|
| 911 |
|
| 912 | raw_spin_unlock_irq(&p->pi_lock);
|
| 913 | put_task_struct(p);
|
| 914 | return ret;
|
| 915 | }
|
| 916 |
|
| 917 | |
| 918 | * No existing pi state. First waiter. [2]
|
| 919 |
|
| 920 | pi_state = alloc_pi_state();
|
| 921 |
|
| 922 | |
| 923 | * Initialize the pi_mutex in locked state and make 'p'
|
| 924 | * the owner of it:
|
| 925 |
|
| 926 | rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
|
| 927 |
|
| 928 |
|
| 929 | pi_state->key = *key;
|
| 930 |
|
| 931 | WARN_ON(!list_empty(&pi_state->list));
|
| 932 | list_add(&pi_state->list, &p->pi_state_list);
|
| 933 | pi_state->owner = p;
|
| 934 | raw_spin_unlock_irq(&p->pi_lock);
|
| 935 |
|
| 936 | put_task_struct(p);
|
| 937 |
|
| 938 | *ps = pi_state;
|
| 939 |
|
| 940 | return 0;
|
| 941 | }
|
| 942 |
|
| 943 | |
| 944 | * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
|
| 945 | * @uaddr: the pi futex user address
|
| 946 | * @hb: the pi futex hash bucket
|
| 947 | * @key: the futex key associated with uaddr and hb
|
| 948 | * @ps: the pi_state pointer where we store the result of the
|
| 949 | * lookup
|
| 950 | * @task: the task to perform the atomic lock work for. This will
|
| 951 | * be "current" except in the case of requeue pi.
|
| 952 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
|
| 953 | *
|
| 954 | * Return:
|
| 955 | * 0 - ready to wait;
|
| 956 | * 1 - acquired the lock;
|
| 957 | * <0 - error
|
| 958 | *
|
| 959 | * The hb->lock and futex_key refs shall be held by the caller.
|
| 960 |
|
| 961 | static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
|
| 962 | union futex_key *key,
|
| 963 | struct futex_pi_state **ps,
|
| 964 | struct task_struct *task, int set_waiters)
|
| 965 | {
|
| 966 | int lock_taken, ret, force_take = 0;
|
| 967 | u32 uval, newval, curval, vpid = task_pid_vnr(task);
|
| 968 |
|
| 969 | retry:
|
| 970 | ret = lock_taken = 0;
|
| 971 |
|
| 972 | |
| 973 | * To avoid races, we attempt to take the lock here again
|
| 974 | * (by doing a 0 -> TID atomic cmpxchg), while holding all
|
| 975 | * the locks. It will most likely not succeed.
|
| 976 |
|
| 977 | newval = vpid;
|
| 978 | if (set_waiters)
|
| 979 | newval |= FUTEX_WAITERS;
|
| 980 |
|
| 981 | if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))
|
| 982 | return -EFAULT;
|
| 983 |
|
| 984 | |
| 985 | * Detect deadlocks.
|
| 986 |
|
| 987 | if ((unlikely((curval & FUTEX_TID_MASK) == vpid)))
|
| 988 | return -EDEADLK;
|
| 989 |
|
| 990 | |
| 991 | * Surprise - we got the lock, but we do not trust user space at all.
|
| 992 |
|
| 993 | if (unlikely(!curval)) {
|
| 994 | |
| 995 | * We verify whether there is kernel state for this
|
| 996 | * futex. If not, we can safely assume, that the 0 ->
|
| 997 | * TID transition is correct. If state exists, we do
|
| 998 | * not bother to fixup the user space state as it was
|
| 999 | * corrupted already.
|
| 1000 |
|
| 1001 | return futex_top_waiter(hb, key) ? -EINVAL : 1;
|
| 1002 | }
|
| 1003 |
|
| 1004 | uval = curval;
|
| 1005 |
|
| 1006 | |
| 1007 | * Set the FUTEX_WAITERS flag, so the owner will know it has someone
|
| 1008 | * to wake at the next unlock.
|
| 1009 |
|
| 1010 | newval = curval | FUTEX_WAITERS;
|
| 1011 |
|
| 1012 | |
| 1013 | * Should we force take the futex? See below.
|
| 1014 |
|
| 1015 | if (unlikely(force_take)) {
|
| 1016 | |
| 1017 | * Keep the OWNER_DIED and the WAITERS bit and set the
|
| 1018 | * new TID value.
|
| 1019 |
|
| 1020 | newval = (curval & ~FUTEX_TID_MASK) | vpid;
|
| 1021 | force_take = 0;
|
| 1022 | lock_taken = 1;
|
| 1023 | }
|
| 1024 |
|
| 1025 | if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
|
| 1026 | return -EFAULT;
|
| 1027 | if (unlikely(curval != uval))
|
| 1028 | goto retry;
|
| 1029 |
|
| 1030 | |
| 1031 | * We took the lock due to forced take over.
|
| 1032 |
|
| 1033 | if (unlikely(lock_taken))
|
| 1034 | return 1;
|
| 1035 |
|
| 1036 | |
| 1037 | * We dont have the lock. Look up the PI state (or create it if
|
| 1038 | * we are the first waiter):
|
| 1039 |
|
| 1040 | ret = lookup_pi_state(uval, hb, key, ps);
|
| 1041 |
|
| 1042 | if (unlikely(ret)) {
|
| 1043 | switch (ret) {
|
| 1044 | case -ESRCH:
|
| 1045 | |
| 1046 | * We failed to find an owner for this
|
| 1047 | * futex. So we have no pi_state to block
|
| 1048 | * on. This can happen in two cases:
|
| 1049 | *
|
| 1050 | * 1) The owner died
|
| 1051 | * 2) A stale FUTEX_WAITERS bit
|
| 1052 | *
|
| 1053 | * Re-read the futex value.
|
| 1054 |
|
| 1055 | if (get_futex_value_locked(&curval, uaddr))
|
| 1056 | return -EFAULT;
|
| 1057 |
|
| 1058 | |
| 1059 | * If the owner died or we have a stale
|
| 1060 | * WAITERS bit the owner TID in the user space
|
| 1061 | * futex is 0.
|
| 1062 |
|
| 1063 | if (!(curval & FUTEX_TID_MASK)) {
|
| 1064 | force_take = 1;
|
| 1065 | goto retry;
|
| 1066 | }
|
| 1067 | default:
|
| 1068 | break;
|
| 1069 | }
|
| 1070 | }
|
| 1071 |
|
| 1072 | return ret;
|
| 1073 | }
|
| 1074 |
|
| 1075 | |
| 1076 | * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
|
| 1077 | * @q: The futex_q to unqueue
|
| 1078 | *
|
| 1079 | * The q->lock_ptr must not be NULL and must be held by the caller.
|
| 1080 |
|
| 1081 | static void __unqueue_futex(struct futex_q *q)
|
| 1082 | {
|
| 1083 | struct futex_hash_bucket *hb;
|
| 1084 |
|
| 1085 | if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
|
| 1086 | || WARN_ON(plist_node_empty(&q->list)))
|
| 1087 | return;
|
| 1088 |
|
| 1089 | hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
|
| 1090 | plist_del(&q->list, &hb->chain);
|
| 1091 | hb_waiters_dec(hb);
|
| 1092 | }
|
| 1093 |
|
| 1094 | |
| 1095 | * The hash bucket lock must be held when this is called.
|
| 1096 | * Afterwards, the futex_q must not be accessed.
|
| 1097 |
|
| 1098 | static void wake_futex(struct futex_q *q)
|
| 1099 | {
|
| 1100 | struct task_struct *p = q->task;
|
| 1101 |
|
| 1102 | if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
|
| 1103 | return;
|
| 1104 |
|
| 1105 | |
| 1106 | * We set q->lock_ptr = NULL _before_ we wake up the task. If
|
| 1107 | * a non-futex wake up happens on another CPU then the task
|
| 1108 | * might exit and p would dereference a non-existing task
|
| 1109 | * struct. Prevent this by holding a reference on p across the
|
| 1110 | * wake up.
|
| 1111 |
|
| 1112 | get_task_struct(p);
|
| 1113 |
|
| 1114 | __unqueue_futex(q);
|
| 1115 | |
| 1116 | * The waiting task can free the futex_q as soon as
|
| 1117 | * q->lock_ptr = NULL is written, without taking any locks. A
|
| 1118 | * memory barrier is required here to prevent the following
|
| 1119 | * store to lock_ptr from getting ahead of the plist_del.
|
| 1120 |
|
| 1121 | smp_wmb();
|
| 1122 | q->lock_ptr = NULL;
|
| 1123 |
|
| 1124 | wake_up_state(p, TASK_NORMAL);
|
| 1125 | put_task_struct(p);
|
| 1126 | }
|
| 1127 |
|
| 1128 | static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
|
| 1129 | {
|
| 1130 | struct task_struct *new_owner;
|
| 1131 | struct futex_pi_state *pi_state = this->pi_state;
|
| 1132 | u32 uninitialized_var(curval), newval;
|
| 1133 | int ret = 0;
|
| 1134 |
|
| 1135 | if (!pi_state)
|
| 1136 | return -EINVAL;
|
| 1137 |
|
| 1138 | |
| 1139 | * If current does not own the pi_state then the futex is
|
| 1140 | * inconsistent and user space fiddled with the futex value.
|
| 1141 |
|
| 1142 | if (pi_state->owner != current)
|
| 1143 | return -EINVAL;
|
| 1144 |
|
| 1145 | raw_spin_lock(&pi_state->pi_mutex.wait_lock);
|
| 1146 | new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
|
| 1147 |
|
| 1148 | |
| 1149 | * It is possible that the next waiter (the one that brought
|
| 1150 | * this owner to the kernel) timed out and is no longer
|
| 1151 | * waiting on the lock.
|
| 1152 |
|
| 1153 | if (!new_owner)
|
| 1154 | new_owner = this->task;
|
| 1155 |
|
| 1156 | |
| 1157 | * We pass it to the next owner. The WAITERS bit is always
|
| 1158 | * kept enabled while there is PI state around. We cleanup the
|
| 1159 | * owner died bit, because we are the owner.
|
| 1160 |
|
| 1161 | newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
|
| 1162 |
|
| 1163 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
|
| 1164 | ret = -EFAULT;
|
| 1165 | else if (curval != uval)
|
| 1166 | ret = -EINVAL;
|
| 1167 | if (ret) {
|
| 1168 | raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
|
| 1169 | return ret;
|
| 1170 | }
|
| 1171 |
|
| 1172 | raw_spin_lock_irq(&pi_state->owner->pi_lock);
|
| 1173 | WARN_ON(list_empty(&pi_state->list));
|
| 1174 | list_del_init(&pi_state->list);
|
| 1175 | raw_spin_unlock_irq(&pi_state->owner->pi_lock);
|
| 1176 |
|
| 1177 | raw_spin_lock_irq(&new_owner->pi_lock);
|
| 1178 | WARN_ON(!list_empty(&pi_state->list));
|
| 1179 | list_add(&pi_state->list, &new_owner->pi_state_list);
|
| 1180 | pi_state->owner = new_owner;
|
| 1181 | raw_spin_unlock_irq(&new_owner->pi_lock);
|
| 1182 |
|
| 1183 | raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
|
| 1184 | rt_mutex_unlock(&pi_state->pi_mutex);
|
| 1185 |
|
| 1186 | return 0;
|
| 1187 | }
|
| 1188 |
|
| 1189 | static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
|
| 1190 | {
|
| 1191 | u32 uninitialized_var(oldval);
|
| 1192 |
|
| 1193 | |
| 1194 | * There is no waiter, so we unlock the futex. The owner died
|
| 1195 | * bit has not to be preserved here. We are the owner:
|
| 1196 |
|
| 1197 | if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))
|
| 1198 | return -EFAULT;
|
| 1199 | if (oldval != uval)
|
| 1200 | return -EAGAIN;
|
| 1201 |
|
| 1202 | return 0;
|
| 1203 | }
|
| 1204 |
|
| 1205 | |
| 1206 | * Express the locking dependencies for lockdep:
|
| 1207 |
|
| 1208 | static inline void
|
| 1209 | double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
|
| 1210 | {
|
| 1211 | if (hb1 <= hb2) {
|
| 1212 | spin_lock(&hb1->lock);
|
| 1213 | if (hb1 < hb2)
|
| 1214 | spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
|
| 1215 | } else {
|
| 1216 | spin_lock(&hb2->lock);
|
| 1217 | spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
|
| 1218 | }
|
| 1219 | }
|
| 1220 |
|
| 1221 | static inline void
|
| 1222 | double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
|
| 1223 | {
|
| 1224 | spin_unlock(&hb1->lock);
|
| 1225 | if (hb1 != hb2)
|
| 1226 | spin_unlock(&hb2->lock);
|
| 1227 | }
|
| 1228 |
|
| 1229 | |
| 1230 | * Wake up waiters matching bitset queued on this futex (uaddr).
|
| 1231 |
|
| 1232 | static int
|
| 1233 | futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
|
| 1234 | {
|
| 1235 | struct futex_hash_bucket *hb;
|
| 1236 | struct futex_q *this, *next;
|
| 1237 | union futex_key key = FUTEX_KEY_INIT;
|
| 1238 | int ret;
|
| 1239 |
|
| 1240 | if (!bitset)
|
| 1241 | return -EINVAL;
|
| 1242 |
|
| 1243 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
|
| 1244 | if (unlikely(ret != 0))
|
| 1245 | goto out;
|
| 1246 |
|
| 1247 | hb = hash_futex(&key);
|
| 1248 |
|
| 1249 |
|
| 1250 | if (!hb_waiters_pending(hb))
|
| 1251 | goto out_put_key;
|
| 1252 |
|
| 1253 | spin_lock(&hb->lock);
|
| 1254 |
|
| 1255 | plist_for_each_entry_safe(this, next, &hb->chain, list) {
|
| 1256 | if (match_futex (&this->key, &key)) {
|
| 1257 | if (this->pi_state || this->rt_waiter) {
|
| 1258 | ret = -EINVAL;
|
| 1259 | break;
|
| 1260 | }
|
| 1261 |
|
| 1262 |
|
| 1263 | if (!(this->bitset & bitset))
|
| 1264 | continue;
|
| 1265 |
|
| 1266 | wake_futex(this);
|
| 1267 | if (++ret >= nr_wake)
|
| 1268 | break;
|
| 1269 | }
|
| 1270 | }
|
| 1271 |
|
| 1272 | spin_unlock(&hb->lock);
|
| 1273 | out_put_key:
|
| 1274 | put_futex_key(&key);
|
| 1275 | out:
|
| 1276 | return ret;
|
| 1277 | }
|
| 1278 |
|
| 1279 | |
| 1280 | * Wake up all waiters hashed on the physical page that is mapped
|
| 1281 | * to this virtual address:
|
| 1282 |
|
| 1283 | static int
|
| 1284 | futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
|
| 1285 | int nr_wake, int nr_wake2, int op)
|
| 1286 | {
|
| 1287 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
|
| 1288 | struct futex_hash_bucket *hb1, *hb2;
|
| 1289 | struct futex_q *this, *next;
|
| 1290 | int ret, op_ret;
|
| 1291 |
|
| 1292 | retry:
|
| 1293 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
|
| 1294 | if (unlikely(ret != 0))
|
| 1295 | goto out;
|
| 1296 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
|
| 1297 | if (unlikely(ret != 0))
|
| 1298 | goto out_put_key1;
|
| 1299 |
|
| 1300 | hb1 = hash_futex(&key1);
|
| 1301 | hb2 = hash_futex(&key2);
|
| 1302 |
|
| 1303 | retry_private:
|
| 1304 | double_lock_hb(hb1, hb2);
|
| 1305 | op_ret = futex_atomic_op_inuser(op, uaddr2);
|
| 1306 | if (unlikely(op_ret < 0)) {
|
| 1307 |
|
| 1308 | double_unlock_hb(hb1, hb2);
|
| 1309 |
|
| 1310 | #ifndef CONFIG_MMU
|
| 1311 | |
| 1312 | * we don't get EFAULT from MMU faults if we don't have an MMU,
|
| 1313 | * but we might get them from range checking
|
| 1314 |
|
| 1315 | ret = op_ret;
|
| 1316 | goto out_put_keys;
|
| 1317 | #endif
|
| 1318 |
|
| 1319 | if (unlikely(op_ret != -EFAULT)) {
|
| 1320 | ret = op_ret;
|
| 1321 | goto out_put_keys;
|
| 1322 | }
|
| 1323 |
|
| 1324 | ret = fault_in_user_writeable(uaddr2);
|
| 1325 | if (ret)
|
| 1326 | goto out_put_keys;
|
| 1327 |
|
| 1328 | if (!(flags & FLAGS_SHARED))
|
| 1329 | goto retry_private;
|
| 1330 |
|
| 1331 | put_futex_key(&key2);
|
| 1332 | put_futex_key(&key1);
|
| 1333 | goto retry;
|
| 1334 | }
|
| 1335 |
|
| 1336 | plist_for_each_entry_safe(this, next, &hb1->chain, list) {
|
| 1337 | if (match_futex (&this->key, &key1)) {
|
| 1338 | if (this->pi_state || this->rt_waiter) {
|
| 1339 | ret = -EINVAL;
|
| 1340 | goto out_unlock;
|
| 1341 | }
|
| 1342 | wake_futex(this);
|
| 1343 | if (++ret >= nr_wake)
|
| 1344 | break;
|
| 1345 | }
|
| 1346 | }
|
| 1347 |
|
| 1348 | if (op_ret > 0) {
|
| 1349 | op_ret = 0;
|
| 1350 | plist_for_each_entry_safe(this, next, &hb2->chain, list) {
|
| 1351 | if (match_futex (&this->key, &key2)) {
|
| 1352 | if (this->pi_state || this->rt_waiter) {
|
| 1353 | ret = -EINVAL;
|
| 1354 | goto out_unlock;
|
| 1355 | }
|
| 1356 | wake_futex(this);
|
| 1357 | if (++op_ret >= nr_wake2)
|
| 1358 | break;
|
| 1359 | }
|
| 1360 | }
|
| 1361 | ret += op_ret;
|
| 1362 | }
|
| 1363 |
|
| 1364 | out_unlock:
|
| 1365 | double_unlock_hb(hb1, hb2);
|
| 1366 | out_put_keys:
|
| 1367 | put_futex_key(&key2);
|
| 1368 | out_put_key1:
|
| 1369 | put_futex_key(&key1);
|
| 1370 | out:
|
| 1371 | return ret;
|
| 1372 | }
|
| 1373 |
|
| 1374 | |
| 1375 | * requeue_futex() - Requeue a futex_q from one hb to another
|
| 1376 | * @q: the futex_q to requeue
|
| 1377 | * @hb1: the source hash_bucket
|
| 1378 | * @hb2: the target hash_bucket
|
| 1379 | * @key2: the new key for the requeued futex_q
|
| 1380 |
|
| 1381 | static inline
|
| 1382 | void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
|
| 1383 | struct futex_hash_bucket *hb2, union futex_key *key2)
|
| 1384 | {
|
| 1385 |
|
| 1386 | |
| 1387 | * If key1 and key2 hash to the same bucket, no need to
|
| 1388 | * requeue.
|
| 1389 |
|
| 1390 | if (likely(&hb1->chain != &hb2->chain)) {
|
| 1391 | plist_del(&q->list, &hb1->chain);
|
| 1392 | hb_waiters_dec(hb1);
|
| 1393 | plist_add(&q->list, &hb2->chain);
|
| 1394 | hb_waiters_inc(hb2);
|
| 1395 | q->lock_ptr = &hb2->lock;
|
| 1396 | }
|
| 1397 | get_futex_key_refs(key2);
|
| 1398 | q->key = *key2;
|
| 1399 | }
|
| 1400 |
|
| 1401 | |
| 1402 | * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
|
| 1403 | * @q: the futex_q
|
| 1404 | * @key: the key of the requeue target futex
|
| 1405 | * @hb: the hash_bucket of the requeue target futex
|
| 1406 | *
|
| 1407 | * During futex_requeue, with requeue_pi=1, it is possible to acquire the
|
| 1408 | * target futex if it is uncontended or via a lock steal. Set the futex_q key
|
| 1409 | * to the requeue target futex so the waiter can detect the wakeup on the right
|
| 1410 | * futex, but remove it from the hb and NULL the rt_waiter so it can detect
|
| 1411 | * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
|
| 1412 | * to protect access to the pi_state to fixup the owner later. Must be called
|
| 1413 | * with both q->lock_ptr and hb->lock held.
|
| 1414 |
|
| 1415 | static inline
|
| 1416 | void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
|
| 1417 | struct futex_hash_bucket *hb)
|
| 1418 | {
|
| 1419 | get_futex_key_refs(key);
|
| 1420 | q->key = *key;
|
| 1421 |
|
| 1422 | __unqueue_futex(q);
|
| 1423 |
|
| 1424 | WARN_ON(!q->rt_waiter);
|
| 1425 | q->rt_waiter = NULL;
|
| 1426 |
|
| 1427 | q->lock_ptr = &hb->lock;
|
| 1428 |
|
| 1429 | wake_up_state(q->task, TASK_NORMAL);
|
| 1430 | }
|
| 1431 |
|
| 1432 | |
| 1433 | * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
|
| 1434 | * @pifutex: the user address of the to futex
|
| 1435 | * @hb1: the from futex hash bucket, must be locked by the caller
|
| 1436 | * @hb2: the to futex hash bucket, must be locked by the caller
|
| 1437 | * @key1: the from futex key
|
| 1438 | * @key2: the to futex key
|
| 1439 | * @ps: address to store the pi_state pointer
|
| 1440 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
|
| 1441 | *
|
| 1442 | * Try and get the lock on behalf of the top waiter if we can do it atomically.
|
| 1443 | * Wake the top waiter if we succeed. If the caller specified set_waiters,
|
| 1444 | * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
|
| 1445 | * hb1 and hb2 must be held by the caller.
|
| 1446 | *
|
| 1447 | * Return:
|
| 1448 | * 0 - failed to acquire the lock atomically;
|
| 1449 | * >0 - acquired the lock, return value is vpid of the top_waiter
|
| 1450 | * <0 - error
|
| 1451 |
|
| 1452 | static int futex_proxy_trylock_atomic(u32 __user *pifutex,
|
| 1453 | struct futex_hash_bucket *hb1,
|
| 1454 | struct futex_hash_bucket *hb2,
|
| 1455 | union futex_key *key1, union futex_key *key2,
|
| 1456 | struct futex_pi_state **ps, int set_waiters)
|
| 1457 | {
|
| 1458 | struct futex_q *top_waiter = NULL;
|
| 1459 | u32 curval;
|
| 1460 | int ret, vpid;
|
| 1461 |
|
| 1462 | if (get_futex_value_locked(&curval, pifutex))
|
| 1463 | return -EFAULT;
|
| 1464 |
|
| 1465 | |
| 1466 | * Find the top_waiter and determine if there are additional waiters.
|
| 1467 | * If the caller intends to requeue more than 1 waiter to pifutex,
|
| 1468 | * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
|
| 1469 | * as we have means to handle the possible fault. If not, don't set
|
| 1470 | * the bit unecessarily as it will force the subsequent unlock to enter
|
| 1471 | * the kernel.
|
| 1472 |
|
| 1473 | top_waiter = futex_top_waiter(hb1, key1);
|
| 1474 |
|
| 1475 |
|
| 1476 | if (!top_waiter)
|
| 1477 | return 0;
|
| 1478 |
|
| 1479 |
|
| 1480 | if (!match_futex(top_waiter->requeue_pi_key, key2))
|
| 1481 | return -EINVAL;
|
| 1482 |
|
| 1483 | |
| 1484 | * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
|
| 1485 | * the contended case or if set_waiters is 1. The pi_state is returned
|
| 1486 | * in ps in contended cases.
|
| 1487 |
|
| 1488 | vpid = task_pid_vnr(top_waiter->task);
|
| 1489 | ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
|
| 1490 | set_waiters);
|
| 1491 | if (ret == 1) {
|
| 1492 | requeue_pi_wake_futex(top_waiter, key2, hb2);
|
| 1493 | return vpid;
|
| 1494 | }
|
| 1495 | return ret;
|
| 1496 | }
|
| 1497 |
|
| 1498 | |
| 1499 | * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
|
| 1500 | * @uaddr1: source futex user address
|
| 1501 | * @flags: futex flags (FLAGS_SHARED, etc.)
|
| 1502 | * @uaddr2: target futex user address
|
| 1503 | * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
|
| 1504 | * @nr_requeue: number of waiters to requeue (0-INT_MAX)
|
| 1505 | * @cmpval: @uaddr1 expected value (or %NULL)
|
| 1506 | * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
|
| 1507 | * pi futex (pi to pi requeue is not supported)
|
| 1508 | *
|
| 1509 | * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
|
| 1510 | * uaddr2 atomically on behalf of the top waiter.
|
| 1511 | *
|
| 1512 | * Return:
|
| 1513 | * >=0 - on success, the number of tasks requeued or woken;
|
| 1514 | * <0 - on error
|
| 1515 |
|
| 1516 | static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
|
| 1517 | u32 __user *uaddr2, int nr_wake, int nr_requeue,
|
| 1518 | u32 *cmpval, int requeue_pi)
|
| 1519 | {
|
| 1520 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
|
| 1521 | int drop_count = 0, task_count = 0, ret;
|
| 1522 | struct futex_pi_state *pi_state = NULL;
|
| 1523 | struct futex_hash_bucket *hb1, *hb2;
|
| 1524 | struct futex_q *this, *next;
|
| 1525 |
|
| 1526 | if (requeue_pi) {
|
| 1527 | |
| 1528 | * Requeue PI only works on two distinct uaddrs. This
|
| 1529 | * check is only valid for private futexes. See below.
|
| 1530 |
|
| 1531 | if (uaddr1 == uaddr2)
|
| 1532 | return -EINVAL;
|
| 1533 |
|
| 1534 | |
| 1535 | * requeue_pi requires a pi_state, try to allocate it now
|
| 1536 | * without any locks in case it fails.
|
| 1537 |
|
| 1538 | if (refill_pi_state_cache())
|
| 1539 | return -ENOMEM;
|
| 1540 | |
| 1541 | * requeue_pi must wake as many tasks as it can, up to nr_wake
|
| 1542 | * + nr_requeue, since it acquires the rt_mutex prior to
|
| 1543 | * returning to userspace, so as to not leave the rt_mutex with
|
| 1544 | * waiters and no owner. However, second and third wake-ups
|
| 1545 | * cannot be predicted as they involve race conditions with the
|
| 1546 | * first wake and a fault while looking up the pi_state. Both
|
| 1547 | * pthread_cond_signal() and pthread_cond_broadcast() should
|
| 1548 | * use nr_wake=1.
|
| 1549 |
|
| 1550 | if (nr_wake != 1)
|
| 1551 | return -EINVAL;
|
| 1552 | }
|
| 1553 |
|
| 1554 | retry:
|
| 1555 | if (pi_state != NULL) {
|
| 1556 | |
| 1557 | * We will have to lookup the pi_state again, so free this one
|
| 1558 | * to keep the accounting correct.
|
| 1559 |
|
| 1560 | free_pi_state(pi_state);
|
| 1561 | pi_state = NULL;
|
| 1562 | }
|
| 1563 |
|
| 1564 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
|
| 1565 | if (unlikely(ret != 0))
|
| 1566 | goto out;
|
| 1567 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
|
| 1568 | requeue_pi ? VERIFY_WRITE : VERIFY_READ);
|
| 1569 | if (unlikely(ret != 0))
|
| 1570 | goto out_put_key1;
|
| 1571 |
|
| 1572 | |
| 1573 | * The check above which compares uaddrs is not sufficient for
|
| 1574 | * shared futexes. We need to compare the keys:
|
| 1575 |
|
| 1576 | if (requeue_pi && match_futex(&key1, &key2)) {
|
| 1577 | ret = -EINVAL;
|
| 1578 | goto out_put_keys;
|
| 1579 | }
|
| 1580 |
|
| 1581 | hb1 = hash_futex(&key1);
|
| 1582 | hb2 = hash_futex(&key2);
|
| 1583 |
|
| 1584 | retry_private:
|
| 1585 | hb_waiters_inc(hb2);
|
| 1586 | double_lock_hb(hb1, hb2);
|
| 1587 |
|
| 1588 | if (likely(cmpval != NULL)) {
|
| 1589 | u32 curval;
|
| 1590 |
|
| 1591 | ret = get_futex_value_locked(&curval, uaddr1);
|
| 1592 |
|
| 1593 | if (unlikely(ret)) {
|
| 1594 | double_unlock_hb(hb1, hb2);
|
| 1595 | hb_waiters_dec(hb2);
|
| 1596 |
|
| 1597 | ret = get_user(curval, uaddr1);
|
| 1598 | if (ret)
|
| 1599 | goto out_put_keys;
|
| 1600 |
|
| 1601 | if (!(flags & FLAGS_SHARED))
|
| 1602 | goto retry_private;
|
| 1603 |
|
| 1604 | put_futex_key(&key2);
|
| 1605 | put_futex_key(&key1);
|
| 1606 | goto retry;
|
| 1607 | }
|
| 1608 | if (curval != *cmpval) {
|
| 1609 | ret = -EAGAIN;
|
| 1610 | goto out_unlock;
|
| 1611 | }
|
| 1612 | }
|
| 1613 |
|
| 1614 | if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
|
| 1615 | |
| 1616 | * Attempt to acquire uaddr2 and wake the top waiter. If we
|
| 1617 | * intend to requeue waiters, force setting the FUTEX_WAITERS
|
| 1618 | * bit. We force this here where we are able to easily handle
|
| 1619 | * faults rather in the requeue loop below.
|
| 1620 |
|
| 1621 | ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
|
| 1622 | &key2, &pi_state, nr_requeue);
|
| 1623 |
|
| 1624 | |
| 1625 | * At this point the top_waiter has either taken uaddr2 or is
|
| 1626 | * waiting on it. If the former, then the pi_state will not
|
| 1627 | * exist yet, look it up one more time to ensure we have a
|
| 1628 | * reference to it. If the lock was taken, ret contains the
|
| 1629 | * vpid of the top waiter task.
|
| 1630 |
|
| 1631 | if (ret > 0) {
|
| 1632 | WARN_ON(pi_state);
|
| 1633 | drop_count++;
|
| 1634 | task_count++;
|
| 1635 | |
| 1636 | * If we acquired the lock, then the user
|
| 1637 | * space value of uaddr2 should be vpid. It
|
| 1638 | * cannot be changed by the top waiter as it
|
| 1639 | * is blocked on hb2 lock if it tries to do
|
| 1640 | * so. If something fiddled with it behind our
|
| 1641 | * back the pi state lookup might unearth
|
| 1642 | * it. So we rather use the known value than
|
| 1643 | * rereading and handing potential crap to
|
| 1644 | * lookup_pi_state.
|
| 1645 |
|
| 1646 | ret = lookup_pi_state(ret, hb2, &key2, &pi_state);
|
| 1647 | }
|
| 1648 |
|
| 1649 | switch (ret) {
|
| 1650 | case 0:
|
| 1651 | break;
|
| 1652 | case -EFAULT:
|
| 1653 | double_unlock_hb(hb1, hb2);
|
| 1654 | hb_waiters_dec(hb2);
|
| 1655 | put_futex_key(&key2);
|
| 1656 | put_futex_key(&key1);
|
| 1657 | ret = fault_in_user_writeable(uaddr2);
|
| 1658 | if (!ret)
|
| 1659 | goto retry;
|
| 1660 | goto out;
|
| 1661 | case -EAGAIN:
|
| 1662 |
|
| 1663 | double_unlock_hb(hb1, hb2);
|
| 1664 | hb_waiters_dec(hb2);
|
| 1665 | put_futex_key(&key2);
|
| 1666 | put_futex_key(&key1);
|
| 1667 | cond_resched();
|
| 1668 | goto retry;
|
| 1669 | default:
|
| 1670 | goto out_unlock;
|
| 1671 | }
|
| 1672 | }
|
| 1673 |
|
| 1674 | plist_for_each_entry_safe(this, next, &hb1->chain, list) {
|
| 1675 | if (task_count - nr_wake >= nr_requeue)
|
| 1676 | break;
|
| 1677 |
|
| 1678 | if (!match_futex(&this->key, &key1))
|
| 1679 | continue;
|
| 1680 |
|
| 1681 | |
| 1682 | * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
|
| 1683 | * be paired with each other and no other futex ops.
|
| 1684 | *
|
| 1685 | * We should never be requeueing a futex_q with a pi_state,
|
| 1686 | * which is awaiting a futex_unlock_pi().
|
| 1687 |
|
| 1688 | if ((requeue_pi && !this->rt_waiter) ||
|
| 1689 | (!requeue_pi && this->rt_waiter) ||
|
| 1690 | this->pi_state) {
|
| 1691 | ret = -EINVAL;
|
| 1692 | break;
|
| 1693 | }
|
| 1694 |
|
| 1695 | |
| 1696 | * Wake nr_wake waiters. For requeue_pi, if we acquired the
|
| 1697 | * lock, we already woke the top_waiter. If not, it will be
|
| 1698 | * woken by futex_unlock_pi().
|
| 1699 |
|
| 1700 | if (++task_count <= nr_wake && !requeue_pi) {
|
| 1701 | wake_futex(this);
|
| 1702 | continue;
|
| 1703 | }
|
| 1704 |
|
| 1705 |
|
| 1706 | if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
|
| 1707 | ret = -EINVAL;
|
| 1708 | break;
|
| 1709 | }
|
| 1710 |
|
| 1711 | |
| 1712 | * Requeue nr_requeue waiters and possibly one more in the case
|
| 1713 | * of requeue_pi if we couldn't acquire the lock atomically.
|
| 1714 |
|
| 1715 | if (requeue_pi) {
|
| 1716 |
|
| 1717 | atomic_inc(&pi_state->refcount);
|
| 1718 | this->pi_state = pi_state;
|
| 1719 | ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
|
| 1720 | this->rt_waiter,
|
| 1721 | this->task, 1);
|
| 1722 | if (ret == 1) {
|
| 1723 |
|
| 1724 | requeue_pi_wake_futex(this, &key2, hb2);
|
| 1725 | drop_count++;
|
| 1726 | continue;
|
| 1727 | } else if (ret) {
|
| 1728 |
|
| 1729 | this->pi_state = NULL;
|
| 1730 | free_pi_state(pi_state);
|
| 1731 | goto out_unlock;
|
| 1732 | }
|
| 1733 | }
|
| 1734 | requeue_futex(this, hb1, hb2, &key2);
|
| 1735 | drop_count++;
|
| 1736 | }
|
| 1737 |
|
| 1738 | out_unlock:
|
| 1739 | double_unlock_hb(hb1, hb2);
|
| 1740 | hb_waiters_dec(hb2);
|
| 1741 |
|
| 1742 | |
| 1743 | * drop_futex_key_refs() must be called outside the spinlocks. During
|
| 1744 | * the requeue we moved futex_q's from the hash bucket at key1 to the
|
| 1745 | * one at key2 and updated their key pointer. We no longer need to
|
| 1746 | * hold the references to key1.
|
| 1747 |
|
| 1748 | while (--drop_count >= 0)
|
| 1749 | drop_futex_key_refs(&key1);
|
| 1750 |
|
| 1751 | out_put_keys:
|
| 1752 | put_futex_key(&key2);
|
| 1753 | out_put_key1:
|
| 1754 | put_futex_key(&key1);
|
| 1755 | out:
|
| 1756 | if (pi_state != NULL)
|
| 1757 | free_pi_state(pi_state);
|
| 1758 | return ret ? ret : task_count;
|
| 1759 | }
|
| 1760 |
|
| 1761 |
|
| 1762 | static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
|
| 1763 | __acquires(&hb->lock)
|
| 1764 | {
|
| 1765 | struct futex_hash_bucket *hb;
|
| 1766 |
|
| 1767 | hb = hash_futex(&q->key);
|
| 1768 |
|
| 1769 | |
| 1770 | * Increment the counter before taking the lock so that
|
| 1771 | * a potential waker won't miss a to-be-slept task that is
|
| 1772 | * waiting for the spinlock. This is safe as all queue_lock()
|
| 1773 | * users end up calling queue_me(). Similarly, for housekeeping,
|
| 1774 | * decrement the counter at queue_unlock() when some error has
|
| 1775 | * occurred and we don't end up adding the task to the list.
|
| 1776 |
|
| 1777 | hb_waiters_inc(hb);
|
| 1778 |
|
| 1779 | q->lock_ptr = &hb->lock;
|
| 1780 |
|
| 1781 | spin_lock(&hb->lock);
|
| 1782 | return hb;
|
| 1783 | }
|
| 1784 |
|
| 1785 | static inline void
|
| 1786 | queue_unlock(struct futex_hash_bucket *hb)
|
| 1787 | __releases(&hb->lock)
|
| 1788 | {
|
| 1789 | spin_unlock(&hb->lock);
|
| 1790 | hb_waiters_dec(hb);
|
| 1791 | }
|
| 1792 |
|
| 1793 | |
| 1794 | * queue_me() - Enqueue the futex_q on the futex_hash_bucket
|
| 1795 | * @q: The futex_q to enqueue
|
| 1796 | * @hb: The destination hash bucket
|
| 1797 | *
|
| 1798 | * The hb->lock must be held by the caller, and is released here. A call to
|
| 1799 | * queue_me() is typically paired with exactly one call to unqueue_me(). The
|
| 1800 | * exceptions involve the PI related operations, which may use unqueue_me_pi()
|
| 1801 | * or nothing if the unqueue is done as part of the wake process and the unqueue
|
| 1802 | * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
|
| 1803 | * an example).
|
| 1804 |
|
| 1805 | static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
|
| 1806 | __releases(&hb->lock)
|
| 1807 | {
|
| 1808 | int prio;
|
| 1809 |
|
| 1810 | |
| 1811 | * The priority used to register this element is
|
| 1812 | * - either the real thread-priority for the real-time threads
|
| 1813 | * (i.e. threads with a priority lower than MAX_RT_PRIO)
|
| 1814 | * - or MAX_RT_PRIO for non-RT threads.
|
| 1815 | * Thus, all RT-threads are woken first in priority order, and
|
| 1816 | * the others are woken last, in FIFO order.
|
| 1817 |
|
| 1818 | prio = min(current->normal_prio, MAX_RT_PRIO);
|
| 1819 |
|
| 1820 | plist_node_init(&q->list, prio);
|
| 1821 | plist_add(&q->list, &hb->chain);
|
| 1822 | q->task = current;
|
| 1823 | spin_unlock(&hb->lock);
|
| 1824 | }
|
| 1825 |
|
| 1826 | |
| 1827 | * unqueue_me() - Remove the futex_q from its futex_hash_bucket
|
| 1828 | * @q: The futex_q to unqueue
|
| 1829 | *
|
| 1830 | * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
|
| 1831 | * be paired with exactly one earlier call to queue_me().
|
| 1832 | *
|
| 1833 | * Return:
|
| 1834 | * 1 - if the futex_q was still queued (and we removed unqueued it);
|
| 1835 | * 0 - if the futex_q was already removed by the waking thread
|
| 1836 |
|
| 1837 | static int unqueue_me(struct futex_q *q)
|
| 1838 | {
|
| 1839 | spinlock_t *lock_ptr;
|
| 1840 | int ret = 0;
|
| 1841 |
|
| 1842 |
|
| 1843 | retry:
|
| 1844 | lock_ptr = q->lock_ptr;
|
| 1845 | barrier();
|
| 1846 | if (lock_ptr != NULL) {
|
| 1847 | spin_lock(lock_ptr);
|
| 1848 | |
| 1849 | * q->lock_ptr can change between reading it and
|
| 1850 | * spin_lock(), causing us to take the wrong lock. This
|
| 1851 | * corrects the race condition.
|
| 1852 | *
|
| 1853 | * Reasoning goes like this: if we have the wrong lock,
|
| 1854 | * q->lock_ptr must have changed (maybe several times)
|
| 1855 | * between reading it and the spin_lock(). It can
|
| 1856 | * change again after the spin_lock() but only if it was
|
| 1857 | * already changed before the spin_lock(). It cannot,
|
| 1858 | * however, change back to the original value. Therefore
|
| 1859 | * we can detect whether we acquired the correct lock.
|
| 1860 |
|
| 1861 | if (unlikely(lock_ptr != q->lock_ptr)) {
|
| 1862 | spin_unlock(lock_ptr);
|
| 1863 | goto retry;
|
| 1864 | }
|
| 1865 | __unqueue_futex(q);
|
| 1866 |
|
| 1867 | BUG_ON(q->pi_state);
|
| 1868 |
|
| 1869 | spin_unlock(lock_ptr);
|
| 1870 | ret = 1;
|
| 1871 | }
|
| 1872 |
|
| 1873 | drop_futex_key_refs(&q->key);
|
| 1874 | return ret;
|
| 1875 | }
|
| 1876 |
|
| 1877 | |
| 1878 | * PI futexes can not be requeued and must remove themself from the
|
| 1879 | * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
|
| 1880 | * and dropped here.
|
| 1881 |
|
| 1882 | static void unqueue_me_pi(struct futex_q *q)
|
| 1883 | __releases(q->lock_ptr)
|
| 1884 | {
|
| 1885 | __unqueue_futex(q);
|
| 1886 |
|
| 1887 | BUG_ON(!q->pi_state);
|
| 1888 | free_pi_state(q->pi_state);
|
| 1889 | q->pi_state = NULL;
|
| 1890 |
|
| 1891 | spin_unlock(q->lock_ptr);
|
| 1892 | }
|
| 1893 |
|
| 1894 | |
| 1895 | * Fixup the pi_state owner with the new owner.
|
| 1896 | *
|
| 1897 | * Must be called with hash bucket lock held and mm->sem held for non
|
| 1898 | * private futexes.
|
| 1899 |
|
| 1900 | static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
|
| 1901 | struct task_struct *newowner)
|
| 1902 | {
|
| 1903 | u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
|
| 1904 | struct futex_pi_state *pi_state = q->pi_state;
|
| 1905 | struct task_struct *oldowner = pi_state->owner;
|
| 1906 | u32 uval, uninitialized_var(curval), newval;
|
| 1907 | int ret;
|
| 1908 |
|
| 1909 |
|
| 1910 | if (!pi_state->owner)
|
| 1911 | newtid |= FUTEX_OWNER_DIED;
|
| 1912 |
|
| 1913 | |
| 1914 | * We are here either because we stole the rtmutex from the
|
| 1915 | * previous highest priority waiter or we are the highest priority
|
| 1916 | * waiter but failed to get the rtmutex the first time.
|
| 1917 | * We have to replace the newowner TID in the user space variable.
|
| 1918 | * This must be atomic as we have to preserve the owner died bit here.
|
| 1919 | *
|
| 1920 | * Note: We write the user space value _before_ changing the pi_state
|
| 1921 | * because we can fault here. Imagine swapped out pages or a fork
|
| 1922 | * that marked all the anonymous memory readonly for cow.
|
| 1923 | *
|
| 1924 | * Modifying pi_state _before_ the user space value would
|
| 1925 | * leave the pi_state in an inconsistent state when we fault
|
| 1926 | * here, because we need to drop the hash bucket lock to
|
| 1927 | * handle the fault. This might be observed in the PID check
|
| 1928 | * in lookup_pi_state.
|
| 1929 |
|
| 1930 | retry:
|
| 1931 | if (get_futex_value_locked(&uval, uaddr))
|
| 1932 | goto handle_fault;
|
| 1933 |
|
| 1934 | while (1) {
|
| 1935 | newval = (uval & FUTEX_OWNER_DIED) | newtid;
|
| 1936 |
|
| 1937 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
|
| 1938 | goto handle_fault;
|
| 1939 | if (curval == uval)
|
| 1940 | break;
|
| 1941 | uval = curval;
|
| 1942 | }
|
| 1943 |
|
| 1944 | |
| 1945 | * We fixed up user space. Now we need to fix the pi_state
|
| 1946 | * itself.
|
| 1947 |
|
| 1948 | if (pi_state->owner != NULL) {
|
| 1949 | raw_spin_lock_irq(&pi_state->owner->pi_lock);
|
| 1950 | WARN_ON(list_empty(&pi_state->list));
|
| 1951 | list_del_init(&pi_state->list);
|
| 1952 | raw_spin_unlock_irq(&pi_state->owner->pi_lock);
|
| 1953 | }
|
| 1954 |
|
| 1955 | pi_state->owner = newowner;
|
| 1956 |
|
| 1957 | raw_spin_lock_irq(&newowner->pi_lock);
|
| 1958 | WARN_ON(!list_empty(&pi_state->list));
|
| 1959 | list_add(&pi_state->list, &newowner->pi_state_list);
|
| 1960 | raw_spin_unlock_irq(&newowner->pi_lock);
|
| 1961 | return 0;
|
| 1962 |
|
| 1963 | |
| 1964 | * To handle the page fault we need to drop the hash bucket
|
| 1965 | * lock here. That gives the other task (either the highest priority
|
| 1966 | * waiter itself or the task which stole the rtmutex) the
|
| 1967 | * chance to try the fixup of the pi_state. So once we are
|
| 1968 | * back from handling the fault we need to check the pi_state
|
| 1969 | * after reacquiring the hash bucket lock and before trying to
|
| 1970 | * do another fixup. When the fixup has been done already we
|
| 1971 | * simply return.
|
| 1972 |
|
| 1973 | handle_fault:
|
| 1974 | spin_unlock(q->lock_ptr);
|
| 1975 |
|
| 1976 | ret = fault_in_user_writeable(uaddr);
|
| 1977 |
|
| 1978 | spin_lock(q->lock_ptr);
|
| 1979 |
|
| 1980 | |
| 1981 | * Check if someone else fixed it for us:
|
| 1982 |
|
| 1983 | if (pi_state->owner != oldowner)
|
| 1984 | return 0;
|
| 1985 |
|
| 1986 | if (ret)
|
| 1987 | return ret;
|
| 1988 |
|
| 1989 | goto retry;
|
| 1990 | }
|
| 1991 |
|
| 1992 | static long futex_wait_restart(struct restart_block *restart);
|
| 1993 |
|
| 1994 | |
| 1995 | * fixup_owner() - Post lock pi_state and corner case management
|
| 1996 | * @uaddr: user address of the futex
|
| 1997 | * @q: futex_q (contains pi_state and access to the rt_mutex)
|
| 1998 | * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
|
| 1999 | *
|
| 2000 | * After attempting to lock an rt_mutex, this function is called to cleanup
|
| 2001 | * the pi_state owner as well as handle race conditions that may allow us to
|
| 2002 | * acquire the lock. Must be called with the hb lock held.
|
| 2003 | *
|
| 2004 | * Return:
|
| 2005 | * 1 - success, lock taken;
|
| 2006 | * 0 - success, lock not taken;
|
| 2007 | * <0 - on error (-EFAULT)
|
| 2008 |
|
| 2009 | static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
|
| 2010 | {
|
| 2011 | struct task_struct *owner;
|
| 2012 | int ret = 0;
|
| 2013 |
|
| 2014 | if (locked) {
|
| 2015 | |
| 2016 | * Got the lock. We might not be the anticipated owner if we
|
| 2017 | * did a lock-steal - fix up the PI-state in that case:
|
| 2018 |
|
| 2019 | if (q->pi_state->owner != current)
|
| 2020 | ret = fixup_pi_state_owner(uaddr, q, current);
|
| 2021 | goto out;
|
| 2022 | }
|
| 2023 |
|
| 2024 | |
| 2025 | * Catch the rare case, where the lock was released when we were on the
|
| 2026 | * way back before we locked the hash bucket.
|
| 2027 |
|
| 2028 | if (q->pi_state->owner == current) {
|
| 2029 | |
| 2030 | * Try to get the rt_mutex now. This might fail as some other
|
| 2031 | * task acquired the rt_mutex after we removed ourself from the
|
| 2032 | * rt_mutex waiters list.
|
| 2033 |
|
| 2034 | if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
|
| 2035 | locked = 1;
|
| 2036 | goto out;
|
| 2037 | }
|
| 2038 |
|
| 2039 | |
| 2040 | * pi_state is incorrect, some other task did a lock steal and
|
| 2041 | * we returned due to timeout or signal without taking the
|
| 2042 | * rt_mutex. Too late.
|
| 2043 |
|
| 2044 | raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
|
| 2045 | owner = rt_mutex_owner(&q->pi_state->pi_mutex);
|
| 2046 | if (!owner)
|
| 2047 | owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
|
| 2048 | raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
|
| 2049 | ret = fixup_pi_state_owner(uaddr, q, owner);
|
| 2050 | goto out;
|
| 2051 | }
|
| 2052 |
|
| 2053 | |
| 2054 | * Paranoia check. If we did not take the lock, then we should not be
|
| 2055 | * the owner of the rt_mutex.
|
| 2056 |
|
| 2057 | if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
|
| 2058 | printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
|
| 2059 | "pi-state %p\n", ret,
|
| 2060 | q->pi_state->pi_mutex.owner,
|
| 2061 | q->pi_state->owner);
|
| 2062 |
|
| 2063 | out:
|
| 2064 | return ret ? ret : locked;
|
| 2065 | }
|
| 2066 |
|
| 2067 | |
| 2068 | * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
|
| 2069 | * @hb: the futex hash bucket, must be locked by the caller
|
| 2070 | * @q: the futex_q to queue up on
|
| 2071 | * @timeout: the prepared hrtimer_sleeper, or null for no timeout
|
| 2072 |
|
| 2073 | static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
|
| 2074 | struct hrtimer_sleeper *timeout)
|
| 2075 | {
|
| 2076 | |
| 2077 | * The task state is guaranteed to be set before another task can
|
| 2078 | * wake it. set_current_state() is implemented using set_mb() and
|
| 2079 | * queue_me() calls spin_unlock() upon completion, both serializing
|
| 2080 | * access to the hash list and forcing another memory barrier.
|
| 2081 |
|
| 2082 | set_current_state(TASK_INTERRUPTIBLE);
|
| 2083 | queue_me(q, hb);
|
| 2084 |
|
| 2085 |
|
| 2086 | if (timeout) {
|
| 2087 | hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
|
| 2088 | if (!hrtimer_active(&timeout->timer))
|
| 2089 | timeout->task = NULL;
|
| 2090 | }
|
| 2091 |
|
| 2092 | |
| 2093 | * If we have been removed from the hash list, then another task
|
| 2094 | * has tried to wake us, and we can skip the call to schedule().
|
| 2095 |
|
| 2096 | if (likely(!plist_node_empty(&q->list))) {
|
| 2097 | |
| 2098 | * If the timer has already expired, current will already be
|
| 2099 | * flagged for rescheduling. Only call schedule if there
|
| 2100 | * is no timeout, or if it has yet to expire.
|
| 2101 |
|
| 2102 | if (!timeout || timeout->task)
|
| 2103 | freezable_schedule();
|
| 2104 | }
|
| 2105 | __set_current_state(TASK_RUNNING);
|
| 2106 | }
|
| 2107 |
|
| 2108 | |
| 2109 | * futex_wait_setup() - Prepare to wait on a futex
|
| 2110 | * @uaddr: the futex userspace address
|
| 2111 | * @val: the expected value
|
| 2112 | * @flags: futex flags (FLAGS_SHARED, etc.)
|
| 2113 | * @q: the associated futex_q
|
| 2114 | * @hb: storage for hash_bucket pointer to be returned to caller
|
| 2115 | *
|
| 2116 | * Setup the futex_q and locate the hash_bucket. Get the futex value and
|
| 2117 | * compare it with the expected value. Handle atomic faults internally.
|
| 2118 | * Return with the hb lock held and a q.key reference on success, and unlocked
|
| 2119 | * with no q.key reference on failure.
|
| 2120 | *
|
| 2121 | * Return:
|
| 2122 | * 0 - uaddr contains val and hb has been locked;
|
| 2123 | * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
|
| 2124 |
|
| 2125 | static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
|
| 2126 | struct futex_q *q, struct futex_hash_bucket **hb)
|
| 2127 | {
|
| 2128 | u32 uval;
|
| 2129 | int ret;
|
| 2130 |
|
| 2131 | |
| 2132 | * Access the page AFTER the hash-bucket is locked.
|
| 2133 | * Order is important:
|
| 2134 | *
|
| 2135 | * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
|
| 2136 | * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
|
| 2137 | *
|
| 2138 | * The basic logical guarantee of a futex is that it blocks ONLY
|
| 2139 | * if cond(var) is known to be true at the time of blocking, for
|
| 2140 | * any cond. If we locked the hash-bucket after testing *uaddr, that
|
| 2141 | * would open a race condition where we could block indefinitely with
|
| 2142 | * cond(var) false, which would violate the guarantee.
|
| 2143 | *
|
| 2144 | * On the other hand, we insert q and release the hash-bucket only
|
| 2145 | * after testing *uaddr. This guarantees that futex_wait() will NOT
|
| 2146 | * absorb a wakeup if *uaddr does not match the desired values
|
| 2147 | * while the syscall executes.
|
| 2148 |
|
| 2149 | retry:
|
| 2150 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
|
| 2151 | if (unlikely(ret != 0))
|
| 2152 | return ret;
|
| 2153 |
|
| 2154 | retry_private:
|
| 2155 | *hb = queue_lock(q);
|
| 2156 |
|
| 2157 | ret = get_futex_value_locked(&uval, uaddr);
|
| 2158 |
|
| 2159 | if (ret) {
|
| 2160 | queue_unlock(*hb);
|
| 2161 |
|
| 2162 | ret = get_user(uval, uaddr);
|
| 2163 | if (ret)
|
| 2164 | goto out;
|
| 2165 |
|
| 2166 | if (!(flags & FLAGS_SHARED))
|
| 2167 | goto retry_private;
|
| 2168 |
|
| 2169 | put_futex_key(&q->key);
|
| 2170 | goto retry;
|
| 2171 | }
|
| 2172 |
|
| 2173 | if (uval != val) {
|
| 2174 | queue_unlock(*hb);
|
| 2175 | ret = -EWOULDBLOCK;
|
| 2176 | }
|
| 2177 |
|
| 2178 | out:
|
| 2179 | if (ret)
|
| 2180 | put_futex_key(&q->key);
|
| 2181 | return ret;
|
| 2182 | }
|
| 2183 |
|
| 2184 | static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
|
| 2185 | ktime_t *abs_time, u32 bitset)
|
| 2186 | {
|
| 2187 | struct hrtimer_sleeper timeout, *to = NULL;
|
| 2188 | struct restart_block *restart;
|
| 2189 | struct futex_hash_bucket *hb;
|
| 2190 | struct futex_q q = futex_q_init;
|
| 2191 | int ret;
|
| 2192 |
|
| 2193 | if (!bitset)
|
| 2194 | return -EINVAL;
|
| 2195 | q.bitset = bitset;
|
| 2196 |
|
| 2197 | if (abs_time) {
|
| 2198 | to = &timeout;
|
| 2199 |
|
| 2200 | hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
|
| 2201 | CLOCK_REALTIME : CLOCK_MONOTONIC,
|
| 2202 | HRTIMER_MODE_ABS);
|
| 2203 | hrtimer_init_sleeper(to, current);
|
| 2204 | hrtimer_set_expires_range_ns(&to->timer, *abs_time,
|
| 2205 | current->timer_slack_ns);
|
| 2206 | }
|
| 2207 |
|
| 2208 | retry:
|
| 2209 | |
| 2210 | * Prepare to wait on uaddr. On success, holds hb lock and increments
|
| 2211 | * q.key refs.
|
| 2212 |
|
| 2213 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
|
| 2214 | if (ret)
|
| 2215 | goto out;
|
| 2216 |
|
| 2217 |
|
| 2218 | futex_wait_queue_me(hb, &q, to);
|
| 2219 |
|
| 2220 |
|
| 2221 | ret = 0;
|
| 2222 |
|
| 2223 | if (!unqueue_me(&q))
|
| 2224 | goto out;
|
| 2225 | ret = -ETIMEDOUT;
|
| 2226 | if (to && !to->task)
|
| 2227 | goto out;
|
| 2228 |
|
| 2229 | |
| 2230 | * We expect signal_pending(current), but we might be the
|
| 2231 | * victim of a spurious wakeup as well.
|
| 2232 |
|
| 2233 | if (!signal_pending(current))
|
| 2234 | goto retry;
|
| 2235 |
|
| 2236 | ret = -ERESTARTSYS;
|
| 2237 | if (!abs_time)
|
| 2238 | goto out;
|
| 2239 |
|
| 2240 | restart = ¤t_thread_info()->restart_block;
|
| 2241 | restart->fn = futex_wait_restart;
|
| 2242 | restart->futex.uaddr = uaddr;
|
| 2243 | restart->futex.val = val;
|
| 2244 | restart->futex.time = abs_time->tv64;
|
| 2245 | restart->futex.bitset = bitset;
|
| 2246 | restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
|
| 2247 |
|
| 2248 | ret = -ERESTART_RESTARTBLOCK;
|
| 2249 |
|
| 2250 | out:
|
| 2251 | if (to) {
|
| 2252 | hrtimer_cancel(&to->timer);
|
| 2253 | destroy_hrtimer_on_stack(&to->timer);
|
| 2254 | }
|
| 2255 | return ret;
|
| 2256 | }
|
| 2257 |
|
| 2258 |
|
| 2259 | static long futex_wait_restart(struct restart_block *restart)
|
| 2260 | {
|
| 2261 | u32 __user *uaddr = restart->futex.uaddr;
|
| 2262 | ktime_t t, *tp = NULL;
|
| 2263 |
|
| 2264 | if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
|
| 2265 | t.tv64 = restart->futex.time;
|
| 2266 | tp = &t;
|
| 2267 | }
|
| 2268 | restart->fn = do_no_restart_syscall;
|
| 2269 |
|
| 2270 | return (long)futex_wait(uaddr, restart->futex.flags,
|
| 2271 | restart->futex.val, tp, restart->futex.bitset);
|
| 2272 | }
|
| 2273 |
|
| 2274 |
|
| 2275 | |
| 2276 | * Userspace tried a 0 -> TID atomic transition of the futex value
|
| 2277 | * and failed. The kernel side here does the whole locking operation:
|
| 2278 | * if there are waiters then it will block, it does PI, etc. (Due to
|
| 2279 | * races the kernel might see a 0 value of the futex too.)
|
| 2280 |
|
| 2281 | static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
|
| 2282 | ktime_t *time, int trylock)
|
| 2283 | {
|
| 2284 | struct hrtimer_sleeper timeout, *to = NULL;
|
| 2285 | struct futex_hash_bucket *hb;
|
| 2286 | struct futex_q q = futex_q_init;
|
| 2287 | int res, ret;
|
| 2288 |
|
| 2289 | if (refill_pi_state_cache())
|
| 2290 | return -ENOMEM;
|
| 2291 |
|
| 2292 | if (time) {
|
| 2293 | to = &timeout;
|
| 2294 | hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
|
| 2295 | HRTIMER_MODE_ABS);
|
| 2296 | hrtimer_init_sleeper(to, current);
|
| 2297 | hrtimer_set_expires(&to->timer, *time);
|
| 2298 | }
|
| 2299 |
|
| 2300 | retry:
|
| 2301 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
|
| 2302 | if (unlikely(ret != 0))
|
| 2303 | goto out;
|
| 2304 |
|
| 2305 | retry_private:
|
| 2306 | hb = queue_lock(&q);
|
| 2307 |
|
| 2308 | ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
|
| 2309 | if (unlikely(ret)) {
|
| 2310 | switch (ret) {
|
| 2311 | case 1:
|
| 2312 |
|
| 2313 | ret = 0;
|
| 2314 | goto out_unlock_put_key;
|
| 2315 | case -EFAULT:
|
| 2316 | goto uaddr_faulted;
|
| 2317 | case -EAGAIN:
|
| 2318 | |
| 2319 | * Task is exiting and we just wait for the
|
| 2320 | * exit to complete.
|
| 2321 |
|
| 2322 | queue_unlock(hb);
|
| 2323 | put_futex_key(&q.key);
|
| 2324 | cond_resched();
|
| 2325 | goto retry;
|
| 2326 | default:
|
| 2327 | goto out_unlock_put_key;
|
| 2328 | }
|
| 2329 | }
|
| 2330 |
|
| 2331 | |
| 2332 | * Only actually queue now that the atomic ops are done:
|
| 2333 |
|
| 2334 | queue_me(&q, hb);
|
| 2335 |
|
| 2336 | WARN_ON(!q.pi_state);
|
| 2337 | |
| 2338 | * Block on the PI mutex:
|
| 2339 |
|
| 2340 | if (!trylock)
|
| 2341 | ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
|
| 2342 | else {
|
| 2343 | ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
|
| 2344 |
|
| 2345 | ret = ret ? 0 : -EWOULDBLOCK;
|
| 2346 | }
|
| 2347 |
|
| 2348 | spin_lock(q.lock_ptr);
|
| 2349 | |
| 2350 | * Fixup the pi_state owner and possibly acquire the lock if we
|
| 2351 | * haven't already.
|
| 2352 |
|
| 2353 | res = fixup_owner(uaddr, &q, !ret);
|
| 2354 | |
| 2355 | * If fixup_owner() returned an error, proprogate that. If it acquired
|
| 2356 | * the lock, clear our -ETIMEDOUT or -EINTR.
|
| 2357 |
|
| 2358 | if (res)
|
| 2359 | ret = (res < 0) ? res : 0;
|
| 2360 |
|
| 2361 | |
| 2362 | * If fixup_owner() faulted and was unable to handle the fault, unlock
|
| 2363 | * it and return the fault to userspace.
|
| 2364 |
|
| 2365 | if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
|
| 2366 | rt_mutex_unlock(&q.pi_state->pi_mutex);
|
| 2367 |
|
| 2368 |
|
| 2369 | unqueue_me_pi(&q);
|
| 2370 |
|
| 2371 | goto out_put_key;
|
| 2372 |
|
| 2373 | out_unlock_put_key:
|
| 2374 | queue_unlock(hb);
|
| 2375 |
|
| 2376 | out_put_key:
|
| 2377 | put_futex_key(&q.key);
|
| 2378 | out:
|
| 2379 | if (to)
|
| 2380 | destroy_hrtimer_on_stack(&to->timer);
|
| 2381 | return ret != -EINTR ? ret : -ERESTARTNOINTR;
|
| 2382 |
|
| 2383 | uaddr_faulted:
|
| 2384 | queue_unlock(hb);
|
| 2385 |
|
| 2386 | ret = fault_in_user_writeable(uaddr);
|
| 2387 | if (ret)
|
| 2388 | goto out_put_key;
|
| 2389 |
|
| 2390 | if (!(flags & FLAGS_SHARED))
|
| 2391 | goto retry_private;
|
| 2392 |
|
| 2393 | put_futex_key(&q.key);
|
| 2394 | goto retry;
|
| 2395 | }
|
| 2396 |
|
| 2397 | |
| 2398 | * Userspace attempted a TID -> 0 atomic transition, and failed.
|
| 2399 | * This is the in-kernel slowpath: we look up the PI state (if any),
|
| 2400 | * and do the rt-mutex unlock.
|
| 2401 |
|
| 2402 | static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
|
| 2403 | {
|
| 2404 | struct futex_hash_bucket *hb;
|
| 2405 | struct futex_q *this, *next;
|
| 2406 | union futex_key key = FUTEX_KEY_INIT;
|
| 2407 | u32 uval, vpid = task_pid_vnr(current);
|
| 2408 | int ret;
|
| 2409 |
|
| 2410 | retry:
|
| 2411 | if (get_user(uval, uaddr))
|
| 2412 | return -EFAULT;
|
| 2413 | |
| 2414 | * We release only a lock we actually own:
|
| 2415 |
|
| 2416 | if ((uval & FUTEX_TID_MASK) != vpid)
|
| 2417 | return -EPERM;
|
| 2418 |
|
| 2419 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
|
| 2420 | if (unlikely(ret != 0))
|
| 2421 | goto out;
|
| 2422 |
|
| 2423 | hb = hash_futex(&key);
|
| 2424 | spin_lock(&hb->lock);
|
| 2425 |
|
| 2426 | |
| 2427 | * To avoid races, try to do the TID -> 0 atomic transition
|
| 2428 | * again. If it succeeds then we can return without waking
|
| 2429 | * anyone else up. We only try this if neither the waiters nor
|
| 2430 | * the owner died bit are set.
|
| 2431 |
|
| 2432 | if (!(uval & ~FUTEX_TID_MASK) &&
|
| 2433 | cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0))
|
| 2434 | goto pi_faulted;
|
| 2435 | |
| 2436 | * Rare case: we managed to release the lock atomically,
|
| 2437 | * no need to wake anyone else up:
|
| 2438 |
|
| 2439 | if (unlikely(uval == vpid))
|
| 2440 | goto out_unlock;
|
| 2441 |
|
| 2442 | |
| 2443 | * Ok, other tasks may need to be woken up - check waiters
|
| 2444 | * and do the wakeup if necessary:
|
| 2445 |
|
| 2446 | plist_for_each_entry_safe(this, next, &hb->chain, list) {
|
| 2447 | if (!match_futex (&this->key, &key))
|
| 2448 | continue;
|
| 2449 | ret = wake_futex_pi(uaddr, uval, this);
|
| 2450 | |
| 2451 | * The atomic access to the futex value
|
| 2452 | * generated a pagefault, so retry the
|
| 2453 | * user-access and the wakeup:
|
| 2454 |
|
| 2455 | if (ret == -EFAULT)
|
| 2456 | goto pi_faulted;
|
| 2457 | goto out_unlock;
|
| 2458 | }
|
| 2459 | |
| 2460 | * No waiters - kernel unlocks the futex:
|
| 2461 |
|
| 2462 | ret = unlock_futex_pi(uaddr, uval);
|
| 2463 | if (ret == -EFAULT)
|
| 2464 | goto pi_faulted;
|
| 2465 |
|
| 2466 | out_unlock:
|
| 2467 | spin_unlock(&hb->lock);
|
| 2468 | put_futex_key(&key);
|
| 2469 |
|
| 2470 | out:
|
| 2471 | return ret;
|
| 2472 |
|
| 2473 | pi_faulted:
|
| 2474 | spin_unlock(&hb->lock);
|
| 2475 | put_futex_key(&key);
|
| 2476 |
|
| 2477 | ret = fault_in_user_writeable(uaddr);
|
| 2478 | if (!ret)
|
| 2479 | goto retry;
|
| 2480 |
|
| 2481 | return ret;
|
| 2482 | }
|
| 2483 |
|
| 2484 | |
| 2485 | * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
|
| 2486 | * @hb: the hash_bucket futex_q was original enqueued on
|
| 2487 | * @q: the futex_q woken while waiting to be requeued
|
| 2488 | * @key2: the futex_key of the requeue target futex
|
| 2489 | * @timeout: the timeout associated with the wait (NULL if none)
|
| 2490 | *
|
| 2491 | * Detect if the task was woken on the initial futex as opposed to the requeue
|
| 2492 | * target futex. If so, determine if it was a timeout or a signal that caused
|
| 2493 | * the wakeup and return the appropriate error code to the caller. Must be
|
| 2494 | * called with the hb lock held.
|
| 2495 | *
|
| 2496 | * Return:
|
| 2497 | * 0 = no early wakeup detected;
|
| 2498 | * <0 = -ETIMEDOUT or -ERESTARTNOINTR
|
| 2499 |
|
| 2500 | static inline
|
| 2501 | int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
|
| 2502 | struct futex_q *q, union futex_key *key2,
|
| 2503 | struct hrtimer_sleeper *timeout)
|
| 2504 | {
|
| 2505 | int ret = 0;
|
| 2506 |
|
| 2507 | |
| 2508 | * With the hb lock held, we avoid races while we process the wakeup.
|
| 2509 | * We only need to hold hb (and not hb2) to ensure atomicity as the
|
| 2510 | * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
|
| 2511 | * It can't be requeued from uaddr2 to something else since we don't
|
| 2512 | * support a PI aware source futex for requeue.
|
| 2513 |
|
| 2514 | if (!match_futex(&q->key, key2)) {
|
| 2515 | WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
|
| 2516 | |
| 2517 | * We were woken prior to requeue by a timeout or a signal.
|
| 2518 | * Unqueue the futex_q and determine which it was.
|
| 2519 |
|
| 2520 | plist_del(&q->list, &hb->chain);
|
| 2521 | hb_waiters_dec(hb);
|
| 2522 |
|
| 2523 |
|
| 2524 | ret = -EWOULDBLOCK;
|
| 2525 | if (timeout && !timeout->task)
|
| 2526 | ret = -ETIMEDOUT;
|
| 2527 | else if (signal_pending(current))
|
| 2528 | ret = -ERESTARTNOINTR;
|
| 2529 | }
|
| 2530 | return ret;
|
| 2531 | }
|
| 2532 |
|
| 2533 | |
| 2534 | * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
|
| 2535 | * @uaddr: the futex we initially wait on (non-pi)
|
| 2536 | * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
|
| 2537 | * the same type, no requeueing from private to shared, etc.
|
| 2538 | * @val: the expected value of uaddr
|
| 2539 | * @abs_time: absolute timeout
|
| 2540 | * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
|
| 2541 | * @uaddr2: the pi futex we will take prior to returning to user-space
|
| 2542 | *
|
| 2543 | * The caller will wait on uaddr and will be requeued by futex_requeue() to
|
| 2544 | * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
|
| 2545 | * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
|
| 2546 | * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
|
| 2547 | * without one, the pi logic would not know which task to boost/deboost, if
|
| 2548 | * there was a need to.
|
| 2549 | *
|
| 2550 | * We call schedule in futex_wait_queue_me() when we enqueue and return there
|
| 2551 | * via the following--
|
| 2552 | * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
|
| 2553 | * 2) wakeup on uaddr2 after a requeue
|
| 2554 | * 3) signal
|
| 2555 | * 4) timeout
|
| 2556 | *
|
| 2557 | * If 3, cleanup and return -ERESTARTNOINTR.
|
| 2558 | *
|
| 2559 | * If 2, we may then block on trying to take the rt_mutex and return via:
|
| 2560 | * 5) successful lock
|
| 2561 | * 6) signal
|
| 2562 | * 7) timeout
|
| 2563 | * 8) other lock acquisition failure
|
| 2564 | *
|
| 2565 | * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
|
| 2566 | *
|
| 2567 | * If 4 or 7, we cleanup and return with -ETIMEDOUT.
|
| 2568 | *
|
| 2569 | * Return:
|
| 2570 | * 0 - On success;
|
| 2571 | * <0 - On error
|
| 2572 |
|
| 2573 | static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
|
| 2574 | u32 val, ktime_t *abs_time, u32 bitset,
|
| 2575 | u32 __user *uaddr2)
|
| 2576 | {
|
| 2577 | struct hrtimer_sleeper timeout, *to = NULL;
|
| 2578 | struct rt_mutex_waiter rt_waiter;
|
| 2579 | struct rt_mutex *pi_mutex = NULL;
|
| 2580 | struct futex_hash_bucket *hb;
|
| 2581 | union futex_key key2 = FUTEX_KEY_INIT;
|
| 2582 | struct futex_q q = futex_q_init;
|
| 2583 | int res, ret;
|
| 2584 |
|
| 2585 | if (uaddr == uaddr2)
|
| 2586 | return -EINVAL;
|
| 2587 |
|
| 2588 | if (!bitset)
|
| 2589 | return -EINVAL;
|
| 2590 |
|
| 2591 | if (abs_time) {
|
| 2592 | to = &timeout;
|
| 2593 | hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
|
| 2594 | CLOCK_REALTIME : CLOCK_MONOTONIC,
|
| 2595 | HRTIMER_MODE_ABS);
|
| 2596 | hrtimer_init_sleeper(to, current);
|
| 2597 | hrtimer_set_expires_range_ns(&to->timer, *abs_time,
|
| 2598 | current->timer_slack_ns);
|
| 2599 | }
|
| 2600 |
|
| 2601 | |
| 2602 | * The waiter is allocated on our stack, manipulated by the requeue
|
| 2603 | * code while we sleep on uaddr.
|
| 2604 |
|
| 2605 | debug_rt_mutex_init_waiter(&rt_waiter);
|
| 2606 | RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
|
| 2607 | RB_CLEAR_NODE(&rt_waiter.tree_entry);
|
| 2608 | rt_waiter.task = NULL;
|
| 2609 |
|
| 2610 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
|
| 2611 | if (unlikely(ret != 0))
|
| 2612 | goto out;
|
| 2613 |
|
| 2614 | q.bitset = bitset;
|
| 2615 | q.rt_waiter = &rt_waiter;
|
| 2616 | q.requeue_pi_key = &key2;
|
| 2617 |
|
| 2618 | |
| 2619 | * Prepare to wait on uaddr. On success, increments q.key (key1) ref
|
| 2620 | * count.
|
| 2621 |
|
| 2622 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
|
| 2623 | if (ret)
|
| 2624 | goto out_key2;
|
| 2625 |
|
| 2626 | |
| 2627 | * The check above which compares uaddrs is not sufficient for
|
| 2628 | * shared futexes. We need to compare the keys:
|
| 2629 |
|
| 2630 | if (match_futex(&q.key, &key2)) {
|
| 2631 | ret = -EINVAL;
|
| 2632 | goto out_put_keys;
|
| 2633 | }
|
| 2634 |
|
| 2635 |
|
| 2636 | futex_wait_queue_me(hb, &q, to);
|
| 2637 |
|
| 2638 | spin_lock(&hb->lock);
|
| 2639 | ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
|
| 2640 | spin_unlock(&hb->lock);
|
| 2641 | if (ret)
|
| 2642 | goto out_put_keys;
|
| 2643 |
|
| 2644 | |
| 2645 | * In order for us to be here, we know our q.key == key2, and since
|
| 2646 | * we took the hb->lock above, we also know that futex_requeue() has
|
| 2647 | * completed and we no longer have to concern ourselves with a wakeup
|
| 2648 | * race with the atomic proxy lock acquisition by the requeue code. The
|
| 2649 | * futex_requeue dropped our key1 reference and incremented our key2
|
| 2650 | * reference count.
|
| 2651 |
|
| 2652 |
|
| 2653 |
|
| 2654 | if (!q.rt_waiter) {
|
| 2655 | |
| 2656 | * Got the lock. We might not be the anticipated owner if we
|
| 2657 | * did a lock-steal - fix up the PI-state in that case.
|
| 2658 |
|
| 2659 | if (q.pi_state && (q.pi_state->owner != current)) {
|
| 2660 | spin_lock(q.lock_ptr);
|
| 2661 | ret = fixup_pi_state_owner(uaddr2, &q, current);
|
| 2662 | spin_unlock(q.lock_ptr);
|
| 2663 | }
|
| 2664 | } else {
|
| 2665 | |
| 2666 | * We have been woken up by futex_unlock_pi(), a timeout, or a
|
| 2667 | * signal. futex_unlock_pi() will not destroy the lock_ptr nor
|
| 2668 | * the pi_state.
|
| 2669 |
|
| 2670 | WARN_ON(!q.pi_state);
|
| 2671 | pi_mutex = &q.pi_state->pi_mutex;
|
| 2672 | ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
|
| 2673 | debug_rt_mutex_free_waiter(&rt_waiter);
|
| 2674 |
|
| 2675 | spin_lock(q.lock_ptr);
|
| 2676 | |
| 2677 | * Fixup the pi_state owner and possibly acquire the lock if we
|
| 2678 | * haven't already.
|
| 2679 |
|
| 2680 | res = fixup_owner(uaddr2, &q, !ret);
|
| 2681 | |
| 2682 | * If fixup_owner() returned an error, proprogate that. If it
|
| 2683 | * acquired the lock, clear -ETIMEDOUT or -EINTR.
|
| 2684 |
|
| 2685 | if (res)
|
| 2686 | ret = (res < 0) ? res : 0;
|
| 2687 |
|
| 2688 |
|
| 2689 | unqueue_me_pi(&q);
|
| 2690 | }
|
| 2691 |
|
| 2692 | |
| 2693 | * If fixup_pi_state_owner() faulted and was unable to handle the
|
| 2694 | * fault, unlock the rt_mutex and return the fault to userspace.
|
| 2695 |
|
| 2696 | if (ret == -EFAULT) {
|
| 2697 | if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
|
| 2698 | rt_mutex_unlock(pi_mutex);
|
| 2699 | } else if (ret == -EINTR) {
|
| 2700 | |
| 2701 | * We've already been requeued, but cannot restart by calling
|
| 2702 | * futex_lock_pi() directly. We could restart this syscall, but
|
| 2703 | * it would detect that the user space "val" changed and return
|
| 2704 | * -EWOULDBLOCK. Save the overhead of the restart and return
|
| 2705 | * -EWOULDBLOCK directly.
|
| 2706 |
|
| 2707 | ret = -EWOULDBLOCK;
|
| 2708 | }
|
| 2709 |
|
| 2710 | out_put_keys:
|
| 2711 | put_futex_key(&q.key);
|
| 2712 | out_key2:
|
| 2713 | put_futex_key(&key2);
|
| 2714 |
|
| 2715 | out:
|
| 2716 | if (to) {
|
| 2717 | hrtimer_cancel(&to->timer);
|
| 2718 | destroy_hrtimer_on_stack(&to->timer);
|
| 2719 | }
|
| 2720 | return ret;
|
| 2721 | }
|
| 2722 |
|
| 2723 | |
| 2724 | * Support for robust futexes: the kernel cleans up held futexes at
|
| 2725 | * thread exit time.
|
| 2726 | *
|
| 2727 | * Implementation: user-space maintains a per-thread list of locks it
|
| 2728 | * is holding. Upon do_exit(), the kernel carefully walks this list,
|
| 2729 | * and marks all locks that are owned by this thread with the
|
| 2730 | * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
|
| 2731 | * always manipulated with the lock held, so the list is private and
|
| 2732 | * per-thread. Userspace also maintains a per-thread 'list_op_pending'
|
| 2733 | * field, to allow the kernel to clean up if the thread dies after
|
| 2734 | * acquiring the lock, but just before it could have added itself to
|
| 2735 | * the list. There can only be one such pending lock.
|
| 2736 |
|
| 2737 |
|
| 2738 | |
| 2739 | * sys_set_robust_list() - Set the robust-futex list head of a task
|
| 2740 | * @head: pointer to the list-head
|
| 2741 | * @len: length of the list-head, as userspace expects
|
| 2742 |
|
| 2743 | SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
|
| 2744 | size_t, len)
|
| 2745 | {
|
| 2746 | if (!futex_cmpxchg_enabled)
|
| 2747 | return -ENOSYS;
|
| 2748 | |
| 2749 | * The kernel knows only one size for now:
|
| 2750 |
|
| 2751 | if (unlikely(len != sizeof(*head)))
|
| 2752 | return -EINVAL;
|
| 2753 |
|
| 2754 | current->robust_list = head;
|
| 2755 |
|
| 2756 | return 0;
|
| 2757 | }
|
| 2758 |
|
| 2759 | |
| 2760 | * sys_get_robust_list() - Get the robust-futex list head of a task
|
| 2761 | * @pid: pid of the process [zero for current task]
|
| 2762 | * @head_ptr: pointer to a list-head pointer, the kernel fills it in
|
| 2763 | * @len_ptr: pointer to a length field, the kernel fills in the header size
|
| 2764 |
|
| 2765 | SYSCALL_DEFINE3(get_robust_list, int, pid,
|
| 2766 | struct robust_list_head __user * __user *, head_ptr,
|
| 2767 | size_t __user *, len_ptr)
|
| 2768 | {
|
| 2769 | struct robust_list_head __user *head;
|
| 2770 | unsigned long ret;
|
| 2771 | struct task_struct *p;
|
| 2772 |
|
| 2773 | if (!futex_cmpxchg_enabled)
|
| 2774 | return -ENOSYS;
|
| 2775 |
|
| 2776 | rcu_read_lock();
|
| 2777 |
|
| 2778 | ret = -ESRCH;
|
| 2779 | if (!pid)
|
| 2780 | p = current;
|
| 2781 | else {
|
| 2782 | p = find_task_by_vpid(pid);
|
| 2783 | if (!p)
|
| 2784 | goto err_unlock;
|
| 2785 | }
|
| 2786 |
|
| 2787 | ret = -EPERM;
|
| 2788 | if (!ptrace_may_access(p, PTRACE_MODE_READ))
|
| 2789 | goto err_unlock;
|
| 2790 |
|
| 2791 | head = p->robust_list;
|
| 2792 | rcu_read_unlock();
|
| 2793 |
|
| 2794 | if (put_user(sizeof(*head), len_ptr))
|
| 2795 | return -EFAULT;
|
| 2796 | return put_user(head, head_ptr);
|
| 2797 |
|
| 2798 | err_unlock:
|
| 2799 | rcu_read_unlock();
|
| 2800 |
|
| 2801 | return ret;
|
| 2802 | }
|
| 2803 |
|
| 2804 | |
| 2805 | * Process a futex-list entry, check whether it's owned by the
|
| 2806 | * dying task, and do notification if so:
|
| 2807 |
|
| 2808 | int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
|
| 2809 | {
|
| 2810 | u32 uval, uninitialized_var(nval), mval;
|
| 2811 |
|
| 2812 | retry:
|
| 2813 | if (get_user(uval, uaddr))
|
| 2814 | return -1;
|
| 2815 |
|
| 2816 | if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
|
| 2817 | |
| 2818 | * Ok, this dying thread is truly holding a futex
|
| 2819 | * of interest. Set the OWNER_DIED bit atomically
|
| 2820 | * via cmpxchg, and if the value had FUTEX_WAITERS
|
| 2821 | * set, wake up a waiter (if any). (We have to do a
|
| 2822 | * futex_wake() even if OWNER_DIED is already set -
|
| 2823 | * to handle the rare but possible case of recursive
|
| 2824 | * thread-death.) The rest of the cleanup is done in
|
| 2825 | * userspace.
|
| 2826 |
|
| 2827 | mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
|
| 2828 | |
| 2829 | * We are not holding a lock here, but we want to have
|
| 2830 | * the pagefault_disable/enable() protection because
|
| 2831 | * we want to handle the fault gracefully. If the
|
| 2832 | * access fails we try to fault in the futex with R/W
|
| 2833 | * verification via get_user_pages. get_user() above
|
| 2834 | * does not guarantee R/W access. If that fails we
|
| 2835 | * give up and leave the futex locked.
|
| 2836 |
|
| 2837 | if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
|
| 2838 | if (fault_in_user_writeable(uaddr))
|
| 2839 | return -1;
|
| 2840 | goto retry;
|
| 2841 | }
|
| 2842 | if (nval != uval)
|
| 2843 | goto retry;
|
| 2844 |
|
| 2845 | |
| 2846 | * Wake robust non-PI futexes here. The wakeup of
|
| 2847 | * PI futexes happens in exit_pi_state():
|
| 2848 |
|
| 2849 | if (!pi && (uval & FUTEX_WAITERS))
|
| 2850 | futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
|
| 2851 | }
|
| 2852 | return 0;
|
| 2853 | }
|
| 2854 |
|
| 2855 | |
| 2856 | * Fetch a robust-list pointer. Bit 0 signals PI futexes:
|
| 2857 |
|
| 2858 | static inline int fetch_robust_entry(struct robust_list __user **entry,
|
| 2859 | struct robust_list __user * __user *head,
|
| 2860 | unsigned int *pi)
|
| 2861 | {
|
| 2862 | unsigned long uentry;
|
| 2863 |
|
| 2864 | if (get_user(uentry, (unsigned long __user *)head))
|
| 2865 | return -EFAULT;
|
| 2866 |
|
| 2867 | *entry = (void __user *)(uentry & ~1UL);
|
| 2868 | *pi = uentry & 1;
|
| 2869 |
|
| 2870 | return 0;
|
| 2871 | }
|
| 2872 |
|
| 2873 | |
| 2874 | * Walk curr->robust_list (very carefully, it's a userspace list!)
|
| 2875 | * and mark any locks found there dead, and notify any waiters.
|
| 2876 | *
|
| 2877 | * We silently return on any sign of list-walking problem.
|
| 2878 |
|
| 2879 | void exit_robust_list(struct task_struct *curr)
|
| 2880 | {
|
| 2881 | struct robust_list_head __user *head = curr->robust_list;
|
| 2882 | struct robust_list __user *entry, *next_entry, *pending;
|
| 2883 | unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
|
| 2884 | unsigned int uninitialized_var(next_pi);
|
| 2885 | unsigned long futex_offset;
|
| 2886 | int rc;
|
| 2887 |
|
| 2888 | if (!futex_cmpxchg_enabled)
|
| 2889 | return;
|
| 2890 |
|
| 2891 | |
| 2892 | * Fetch the list head (which was registered earlier, via
|
| 2893 | * sys_set_robust_list()):
|
| 2894 |
|
| 2895 | if (fetch_robust_entry(&entry, &head->list.next, &pi))
|
| 2896 | return;
|
| 2897 | |
| 2898 | * Fetch the relative futex offset:
|
| 2899 |
|
| 2900 | if (get_user(futex_offset, &head->futex_offset))
|
| 2901 | return;
|
| 2902 | |
| 2903 | * Fetch any possibly pending lock-add first, and handle it
|
| 2904 | * if it exists:
|
| 2905 |
|
| 2906 | if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
|
| 2907 | return;
|
| 2908 |
|
| 2909 | next_entry = NULL;
|
| 2910 | while (entry != &head->list) {
|
| 2911 | |
| 2912 | * Fetch the next entry in the list before calling
|
| 2913 | * handle_futex_death:
|
| 2914 |
|
| 2915 | rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
|
| 2916 | |
| 2917 | * A pending lock might already be on the list, so
|
| 2918 | * don't process it twice:
|
| 2919 |
|
| 2920 | if (entry != pending)
|
| 2921 | if (handle_futex_death((void __user *)entry + futex_offset,
|
| 2922 | curr, pi))
|
| 2923 | return;
|
| 2924 | if (rc)
|
| 2925 | return;
|
| 2926 | entry = next_entry;
|
| 2927 | pi = next_pi;
|
| 2928 | |
| 2929 | * Avoid excessively long or circular lists:
|
| 2930 |
|
| 2931 | if (!--limit)
|
| 2932 | break;
|
| 2933 |
|
| 2934 | cond_resched();
|
| 2935 | }
|
| 2936 |
|
| 2937 | if (pending)
|
| 2938 | handle_futex_death((void __user *)pending + futex_offset,
|
| 2939 | curr, pip);
|
| 2940 | }
|
| 2941 |
|
| 2942 | long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
|
| 2943 | u32 __user *uaddr2, u32 val2, u32 val3)
|
| 2944 | {
|
| 2945 | int cmd = op & FUTEX_CMD_MASK;
|
| 2946 | unsigned int flags = 0;
|
| 2947 |
|
| 2948 | if (!(op & FUTEX_PRIVATE_FLAG))
|
| 2949 | flags |= FLAGS_SHARED;
|
| 2950 |
|
| 2951 | if (op & FUTEX_CLOCK_REALTIME) {
|
| 2952 | flags |= FLAGS_CLOCKRT;
|
| 2953 | if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
|
| 2954 | return -ENOSYS;
|
| 2955 | }
|
| 2956 |
|
| 2957 | switch (cmd) {
|
| 2958 | case FUTEX_LOCK_PI:
|
| 2959 | case FUTEX_UNLOCK_PI:
|
| 2960 | case FUTEX_TRYLOCK_PI:
|
| 2961 | case FUTEX_WAIT_REQUEUE_PI:
|
| 2962 | case FUTEX_CMP_REQUEUE_PI:
|
| 2963 | if (!futex_cmpxchg_enabled)
|
| 2964 | return -ENOSYS;
|
| 2965 | }
|
| 2966 |
|
| 2967 | switch (cmd) {
|
| 2968 | case FUTEX_WAIT:
|
| 2969 | val3 = FUTEX_BITSET_MATCH_ANY;
|
| 2970 | case FUTEX_WAIT_BITSET:
|
| 2971 | return futex_wait(uaddr, flags, val, timeout, val3);
|
| 2972 | case FUTEX_WAKE:
|
| 2973 | val3 = FUTEX_BITSET_MATCH_ANY;
|
| 2974 | case FUTEX_WAKE_BITSET:
|
| 2975 | return futex_wake(uaddr, flags, val, val3);
|
| 2976 | case FUTEX_REQUEUE:
|
| 2977 | return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
|
| 2978 | case FUTEX_CMP_REQUEUE:
|
| 2979 | return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
|
| 2980 | case FUTEX_WAKE_OP:
|
| 2981 | return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
|
| 2982 | case FUTEX_LOCK_PI:
|
| 2983 | return futex_lock_pi(uaddr, flags, val, timeout, 0);
|
| 2984 | case FUTEX_UNLOCK_PI:
|
| 2985 | return futex_unlock_pi(uaddr, flags);
|
| 2986 | case FUTEX_TRYLOCK_PI:
|
| 2987 | return futex_lock_pi(uaddr, flags, 0, timeout, 1);
|
| 2988 | case FUTEX_WAIT_REQUEUE_PI:
|
| 2989 | val3 = FUTEX_BITSET_MATCH_ANY;
|
| 2990 | return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
|
| 2991 | uaddr2);
|
| 2992 | case FUTEX_CMP_REQUEUE_PI:
|
| 2993 | return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
|
| 2994 | }
|
| 2995 | return -ENOSYS;
|
| 2996 | }
|
| 2997 |
|
| 2998 |
|
| 2999 | SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
|
| 3000 | struct timespec __user *, utime, u32 __user *, uaddr2,
|
| 3001 | u32, val3)
|
| 3002 | {
|
| 3003 | struct timespec ts;
|
| 3004 | ktime_t t, *tp = NULL;
|
| 3005 | u32 val2 = 0;
|
| 3006 | int cmd = op & FUTEX_CMD_MASK;
|
| 3007 |
|
| 3008 | if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
|
| 3009 | cmd == FUTEX_WAIT_BITSET ||
|
| 3010 | cmd == FUTEX_WAIT_REQUEUE_PI)) {
|
| 3011 | if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
|
| 3012 | return -EFAULT;
|
| 3013 | if (!timespec_valid(&ts))
|
| 3014 | return -EINVAL;
|
| 3015 |
|
| 3016 | t = timespec_to_ktime(ts);
|
| 3017 | if (cmd == FUTEX_WAIT)
|
| 3018 | t = ktime_add_safe(ktime_get(), t);
|
| 3019 | tp = &t;
|
| 3020 | }
|
| 3021 | |
| 3022 | * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
|
| 3023 | * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
|
| 3024 |
|
| 3025 | if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
|
| 3026 | cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
|
| 3027 | val2 = (u32) (unsigned long) utime;
|
| 3028 |
|
| 3029 | return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
|
| 3030 | }
|
| 3031 |
|
| 3032 | static void __init futex_detect_cmpxchg(void)
|
| 3033 | {
|
| 3034 | #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
|
| 3035 | u32 curval;
|
| 3036 |
|
| 3037 | |
| 3038 | * This will fail and we want it. Some arch implementations do
|
| 3039 | * runtime detection of the futex_atomic_cmpxchg_inatomic()
|
| 3040 | * functionality. We want to know that before we call in any
|
| 3041 | * of the complex code paths. Also we want to prevent
|
| 3042 | * registration of robust lists in that case. NULL is
|
| 3043 | * guaranteed to fault and we get -EFAULT on functional
|
| 3044 | * implementation, the non-functional ones will return
|
| 3045 | * -ENOSYS.
|
| 3046 |
|
| 3047 | if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
|
| 3048 | futex_cmpxchg_enabled = 1;
|
| 3049 | #endif
|
| 3050 | }
|
| 3051 |
|
| 3052 | static int __init futex_init(void)
|
| 3053 | {
|
| 3054 | unsigned int futex_shift;
|
| 3055 | unsigned long i;
|
| 3056 |
|
| 3057 | #if CONFIG_BASE_SMALL
|
| 3058 | futex_hashsize = 16;
|
| 3059 | #else
|
| 3060 | futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
|
| 3061 | #endif
|
| 3062 |
|
| 3063 | futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
|
| 3064 | futex_hashsize, 0,
|
| 3065 | futex_hashsize < 256 ? HASH_SMALL : 0,
|
| 3066 | &futex_shift, NULL,
|
| 3067 | futex_hashsize, futex_hashsize);
|
| 3068 | futex_hashsize = 1UL << futex_shift;
|
| 3069 |
|
| 3070 | futex_detect_cmpxchg();
|
| 3071 |
|
| 3072 | for (i = 0; i < futex_hashsize; i++) {
|
| 3073 | atomic_set(&futex_queues[i].waiters, 0);
|
| 3074 | plist_head_init(&futex_queues[i].chain);
|
| 3075 | spin_lock_init(&futex_queues[i].lock);
|
| 3076 | }
|
| 3077 |
|
| 3078 | return 0;
|
| 3079 | }
|
| 3080 | __initcall(futex_init);
|