| 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 | #include <linux/fault-inject.h>
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| 68 |
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| 69 | #include <asm/futex.h>
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| 70 |
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| 71 | #include "locking/rtmutex_common.h"
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| 72 |
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| 73 | |
| 74 | * READ this before attempting to hack on futexes!
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| 75 | *
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| 76 | * Basic futex operation and ordering guarantees
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| 77 | * =============================================
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| 78 | *
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| 79 | * The waiter reads the futex value in user space and calls
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| 80 | * futex_wait(). This function computes the hash bucket and acquires
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| 81 | * the hash bucket lock. After that it reads the futex user space value
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| 82 | * again and verifies that the data has not changed. If it has not changed
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| 83 | * it enqueues itself into the hash bucket, releases the hash bucket lock
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| 84 | * and schedules.
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| 85 | *
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| 86 | * The waker side modifies the user space value of the futex and calls
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| 87 | * futex_wake(). This function computes the hash bucket and acquires the
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| 88 | * hash bucket lock. Then it looks for waiters on that futex in the hash
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| 89 | * bucket and wakes them.
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| 90 | *
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| 91 | * In futex wake up scenarios where no tasks are blocked on a futex, taking
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| 92 | * the hb spinlock can be avoided and simply return. In order for this
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| 93 | * optimization to work, ordering guarantees must exist so that the waiter
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| 94 | * being added to the list is acknowledged when the list is concurrently being
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| 95 | * checked by the waker, avoiding scenarios like the following:
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| 96 | *
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| 97 | * CPU 0 CPU 1
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| 98 | * val = *futex;
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| 99 | * sys_futex(WAIT, futex, val);
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| 100 | * futex_wait(futex, val);
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| 101 | * uval = *futex;
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| 102 | * *futex = newval;
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| 103 | * sys_futex(WAKE, futex);
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| 104 | * futex_wake(futex);
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| 105 | * if (queue_empty())
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| 106 | * return;
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| 107 | * if (uval == val)
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| 108 | * lock(hash_bucket(futex));
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| 109 | * queue();
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| 110 | * unlock(hash_bucket(futex));
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| 111 | * schedule();
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| 112 | *
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| 113 | * This would cause the waiter on CPU 0 to wait forever because it
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| 114 | * missed the transition of the user space value from val to newval
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| 115 | * and the waker did not find the waiter in the hash bucket queue.
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| 116 | *
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| 117 | * The correct serialization ensures that a waiter either observes
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| 118 | * the changed user space value before blocking or is woken by a
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| 119 | * concurrent waker:
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| 120 | *
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| 121 | * CPU 0 CPU 1
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| 122 | * val = *futex;
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| 123 | * sys_futex(WAIT, futex, val);
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| 124 | * futex_wait(futex, val);
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| 125 | *
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| 126 | * waiters++; (a)
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| 127 | * mb(); (A) <-- paired with -.
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| 128 | * |
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| 129 | * lock(hash_bucket(futex)); |
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| 130 | * |
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| 131 | * uval = *futex; |
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| 132 | * | *futex = newval;
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| 133 | * | sys_futex(WAKE, futex);
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| 134 | * | futex_wake(futex);
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| 135 | * |
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| 136 | * `-------> mb(); (B)
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| 137 | * if (uval == val)
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| 138 | * queue();
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| 139 | * unlock(hash_bucket(futex));
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| 140 | * schedule(); if (waiters)
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| 141 | * lock(hash_bucket(futex));
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| 142 | * else wake_waiters(futex);
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| 143 | * waiters--; (b) unlock(hash_bucket(futex));
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| 144 | *
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| 145 | * Where (A) orders the waiters increment and the futex value read through
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| 146 | * atomic operations (see hb_waiters_inc) and where (B) orders the write
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| 147 | * to futex and the waiters read -- this is done by the barriers for both
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| 148 | * shared and private futexes in get_futex_key_refs().
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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 | |
| 259 | * The base of the bucket array and its size are always used together
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| 260 | * (after initialization only in hash_futex()), so ensure that they
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| 261 | * reside in the same cacheline.
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| 262 |
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| 263 | static struct {
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| 264 | struct futex_hash_bucket *queues;
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| 265 | unsigned long hashsize;
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| 266 | } __futex_data __read_mostly __aligned(2*sizeof(long));
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| 267 | #define futex_queues (__futex_data.queues)
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| 268 | #define futex_hashsize (__futex_data.hashsize)
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| 269 |
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| 270 |
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| 271 | |
| 272 | * Fault injections for futexes.
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| 273 |
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| 274 | #ifdef CONFIG_FAIL_FUTEX
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| 275 |
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| 276 | static struct {
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| 277 | struct fault_attr attr;
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| 278 |
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| 279 | bool ignore_private;
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| 280 | } fail_futex = {
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| 281 | .attr = FAULT_ATTR_INITIALIZER,
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| 282 | .ignore_private = false,
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| 283 | };
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| 284 |
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| 285 | static int __init setup_fail_futex(char *str)
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| 286 | {
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| 287 | return setup_fault_attr(&fail_futex.attr, str);
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| 288 | }
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| 289 | __setup("fail_futex=", setup_fail_futex);
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| 290 |
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| 291 | static bool should_fail_futex(bool fshared)
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| 292 | {
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| 293 | if (fail_futex.ignore_private && !fshared)
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| 294 | return false;
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| 295 |
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| 296 | return should_fail(&fail_futex.attr, 1);
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| 297 | }
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| 298 |
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| 299 | #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
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| 300 |
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| 301 | static int __init fail_futex_debugfs(void)
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| 302 | {
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| 303 | umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
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| 304 | struct dentry *dir;
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| 305 |
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| 306 | dir = fault_create_debugfs_attr("fail_futex", NULL,
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| 307 | &fail_futex.attr);
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| 308 | if (IS_ERR(dir))
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| 309 | return PTR_ERR(dir);
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| 310 |
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| 311 | if (!debugfs_create_bool("ignore-private", mode, dir,
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| 312 | &fail_futex.ignore_private)) {
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| 313 | debugfs_remove_recursive(dir);
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| 314 | return -ENOMEM;
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| 315 | }
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| 316 |
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| 317 | return 0;
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| 318 | }
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| 319 |
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| 320 | late_initcall(fail_futex_debugfs);
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| 321 |
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| 322 | #endif
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| 323 |
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| 324 | #else
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| 325 | static inline bool should_fail_futex(bool fshared)
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| 326 | {
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| 327 | return false;
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| 328 | }
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| 329 | #endif
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| 330 |
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| 331 | static inline void futex_get_mm(union futex_key *key)
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| 332 | {
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| 333 | atomic_inc(&key->private.mm->mm_count);
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| 334 | |
| 335 | * Ensure futex_get_mm() implies a full barrier such that
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| 336 | * get_futex_key() implies a full barrier. This is relied upon
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| 337 | * as full barrier (B), see the ordering comment above.
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| 338 |
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| 339 | smp_mb__after_atomic();
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| 340 | }
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| 341 |
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| 342 | |
| 343 | * Reflects a new waiter being added to the waitqueue.
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| 344 |
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| 345 | static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
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| 346 | {
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| 347 | #ifdef CONFIG_SMP
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| 348 | atomic_inc(&hb->waiters);
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| 349 | |
| 350 | * Full barrier (A), see the ordering comment above.
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| 351 |
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| 352 | smp_mb__after_atomic();
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| 353 | #endif
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| 354 | }
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| 355 |
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| 356 | |
| 357 | * Reflects a waiter being removed from the waitqueue by wakeup
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| 358 | * paths.
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| 359 |
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| 360 | static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
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| 361 | {
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| 362 | #ifdef CONFIG_SMP
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| 363 | atomic_dec(&hb->waiters);
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| 364 | #endif
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| 365 | }
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| 366 |
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| 367 | static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
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| 368 | {
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| 369 | #ifdef CONFIG_SMP
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| 370 | return atomic_read(&hb->waiters);
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| 371 | #else
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| 372 | return 1;
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| 373 | #endif
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| 374 | }
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| 375 |
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| 376 | |
| 377 | * We hash on the keys returned from get_futex_key (see below).
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| 378 |
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| 379 | static struct futex_hash_bucket *hash_futex(union futex_key *key)
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| 380 | {
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| 381 | u32 hash = jhash2((u32*)&key->both.word,
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| 382 | (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
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| 383 | key->both.offset);
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| 384 | return &futex_queues[hash & (futex_hashsize - 1)];
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| 385 | }
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| 386 |
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| 387 | |
| 388 | * Return 1 if two futex_keys are equal, 0 otherwise.
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| 389 |
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| 390 | static inline int match_futex(union futex_key *key1, union futex_key *key2)
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| 391 | {
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| 392 | return (key1 && key2
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| 393 | && key1->both.word == key2->both.word
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| 394 | && key1->both.ptr == key2->both.ptr
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| 395 | && key1->both.offset == key2->both.offset);
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| 396 | }
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| 397 |
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| 398 | |
| 399 | * Take a reference to the resource addressed by a key.
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| 400 | * Can be called while holding spinlocks.
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| 401 | *
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| 402 |
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| 403 | static void get_futex_key_refs(union futex_key *key)
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| 404 | {
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| 405 | if (!key->both.ptr)
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| 406 | return;
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| 407 |
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| 408 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
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| 409 | case FUT_OFF_INODE:
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| 410 | ihold(key->shared.inode);
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| 411 | break;
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| 412 | case FUT_OFF_MMSHARED:
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| 413 | futex_get_mm(key);
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| 414 | break;
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| 415 | default:
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| 416 | |
| 417 | * Private futexes do not hold reference on an inode or
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| 418 | * mm, therefore the only purpose of calling get_futex_key_refs
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| 419 | * is because we need the barrier for the lockless waiter check.
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| 420 |
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| 421 | smp_mb();
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| 422 | }
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| 423 | }
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| 424 |
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| 425 | |
| 426 | * Drop a reference to the resource addressed by a key.
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| 427 | * The hash bucket spinlock must not be held. This is
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| 428 | * a no-op for private futexes, see comment in the get
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| 429 | * counterpart.
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| 430 |
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| 431 | static void drop_futex_key_refs(union futex_key *key)
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| 432 | {
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| 433 | if (!key->both.ptr) {
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| 434 |
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| 435 | WARN_ON_ONCE(1);
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| 436 | return;
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| 437 | }
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| 438 |
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| 439 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
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| 440 | case FUT_OFF_INODE:
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| 441 | iput(key->shared.inode);
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| 442 | break;
|
| 443 | case FUT_OFF_MMSHARED:
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| 444 | mmdrop(key->private.mm);
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| 445 | break;
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| 446 | }
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| 447 | }
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| 448 |
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| 449 | |
| 450 | * get_futex_key() - Get parameters which are the keys for a futex
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| 451 | * @uaddr: virtual address of the futex
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| 452 | * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
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| 453 | * @key: address where result is stored.
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| 454 | * @rw: mapping needs to be read/write (values: VERIFY_READ,
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| 455 | * VERIFY_WRITE)
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| 456 | *
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| 457 | * Return: a negative error code or 0
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| 458 | *
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| 459 | * The key words are stored in *key on success.
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| 460 | *
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| 461 | * For shared mappings, it's (page->index, file_inode(vma->vm_file),
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| 462 | * offset_within_page). For private mappings, it's (uaddr, current->mm).
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| 463 | * We can usually work out the index without swapping in the page.
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| 464 | *
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| 465 | * lock_page() might sleep, the caller should not hold a spinlock.
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| 466 |
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| 467 | static int
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| 468 | get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
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| 469 | {
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| 470 | unsigned long address = (unsigned long)uaddr;
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| 471 | struct mm_struct *mm = current->mm;
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| 472 | struct page *page, *page_head;
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| 473 | int err, ro = 0;
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| 474 |
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| 475 | |
| 476 | * The futex address must be "naturally" aligned.
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| 477 |
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| 478 | key->both.offset = address % PAGE_SIZE;
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| 479 | if (unlikely((address % sizeof(u32)) != 0))
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| 480 | return -EINVAL;
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| 481 | address -= key->both.offset;
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| 482 |
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| 483 | if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
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| 484 | return -EFAULT;
|
| 485 |
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| 486 | if (unlikely(should_fail_futex(fshared)))
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| 487 | return -EFAULT;
|
| 488 |
|
| 489 | |
| 490 | * PROCESS_PRIVATE futexes are fast.
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| 491 | * As the mm cannot disappear under us and the 'key' only needs
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| 492 | * virtual address, we dont even have to find the underlying vma.
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| 493 | * Note : We do have to check 'uaddr' is a valid user address,
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| 494 | * but access_ok() should be faster than find_vma()
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| 495 |
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| 496 | if (!fshared) {
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| 497 | key->private.mm = mm;
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| 498 | key->private.address = address;
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| 499 | get_futex_key_refs(key);
|
| 500 | return 0;
|
| 501 | }
|
| 502 |
|
| 503 | again:
|
| 504 |
|
| 505 | if (unlikely(should_fail_futex(fshared)))
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| 506 | return -EFAULT;
|
| 507 |
|
| 508 | err = get_user_pages_fast(address, 1, 1, &page);
|
| 509 | |
| 510 | * If write access is not required (eg. FUTEX_WAIT), try
|
| 511 | * and get read-only access.
|
| 512 |
|
| 513 | if (err == -EFAULT && rw == VERIFY_READ) {
|
| 514 | err = get_user_pages_fast(address, 1, 0, &page);
|
| 515 | ro = 1;
|
| 516 | }
|
| 517 | if (err < 0)
|
| 518 | return err;
|
| 519 | else
|
| 520 | err = 0;
|
| 521 |
|
| 522 | #ifdef CONFIG_TRANSPARENT_HUGEPAGE
|
| 523 | page_head = page;
|
| 524 | if (unlikely(PageTail(page))) {
|
| 525 | put_page(page);
|
| 526 |
|
| 527 | local_irq_disable();
|
| 528 | if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) {
|
| 529 | page_head = compound_head(page);
|
| 530 | |
| 531 | * page_head is valid pointer but we must pin
|
| 532 | * it before taking the PG_lock and/or
|
| 533 | * PG_compound_lock. The moment we re-enable
|
| 534 | * irqs __split_huge_page_splitting() can
|
| 535 | * return and the head page can be freed from
|
| 536 | * under us. We can't take the PG_lock and/or
|
| 537 | * PG_compound_lock on a page that could be
|
| 538 | * freed from under us.
|
| 539 |
|
| 540 | if (page != page_head) {
|
| 541 | get_page(page_head);
|
| 542 | put_page(page);
|
| 543 | }
|
| 544 | local_irq_enable();
|
| 545 | } else {
|
| 546 | local_irq_enable();
|
| 547 | goto again;
|
| 548 | }
|
| 549 | }
|
| 550 | #else
|
| 551 | page_head = compound_head(page);
|
| 552 | if (page != page_head) {
|
| 553 | get_page(page_head);
|
| 554 | put_page(page);
|
| 555 | }
|
| 556 | #endif
|
| 557 |
|
| 558 | lock_page(page_head);
|
| 559 |
|
| 560 | |
| 561 | * If page_head->mapping is NULL, then it cannot be a PageAnon
|
| 562 | * page; but it might be the ZERO_PAGE or in the gate area or
|
| 563 | * in a special mapping (all cases which we are happy to fail);
|
| 564 | * or it may have been a good file page when get_user_pages_fast
|
| 565 | * found it, but truncated or holepunched or subjected to
|
| 566 | * invalidate_complete_page2 before we got the page lock (also
|
| 567 | * cases which we are happy to fail). And we hold a reference,
|
| 568 | * so refcount care in invalidate_complete_page's remove_mapping
|
| 569 | * prevents drop_caches from setting mapping to NULL beneath us.
|
| 570 | *
|
| 571 | * The case we do have to guard against is when memory pressure made
|
| 572 | * shmem_writepage move it from filecache to swapcache beneath us:
|
| 573 | * an unlikely race, but we do need to retry for page_head->mapping.
|
| 574 |
|
| 575 | if (!page_head->mapping) {
|
| 576 | int shmem_swizzled = PageSwapCache(page_head);
|
| 577 | unlock_page(page_head);
|
| 578 | put_page(page_head);
|
| 579 | if (shmem_swizzled)
|
| 580 | goto again;
|
| 581 | return -EFAULT;
|
| 582 | }
|
| 583 |
|
| 584 | |
| 585 | * Private mappings are handled in a simple way.
|
| 586 | *
|
| 587 | * NOTE: When userspace waits on a MAP_SHARED mapping, even if
|
| 588 | * it's a read-only handle, it's expected that futexes attach to
|
| 589 | * the object not the particular process.
|
| 590 |
|
| 591 | if (PageAnon(page_head)) {
|
| 592 | |
| 593 | * A RO anonymous page will never change and thus doesn't make
|
| 594 | * sense for futex operations.
|
| 595 |
|
| 596 | if (unlikely(should_fail_futex(fshared)) || ro) {
|
| 597 | err = -EFAULT;
|
| 598 | goto out;
|
| 599 | }
|
| 600 |
|
| 601 | key->both.offset |= FUT_OFF_MMSHARED;
|
| 602 | key->private.mm = mm;
|
| 603 | key->private.address = address;
|
| 604 | } else {
|
| 605 | key->both.offset |= FUT_OFF_INODE;
|
| 606 | key->shared.inode = page_head->mapping->host;
|
| 607 | key->shared.pgoff = basepage_index(page);
|
| 608 | }
|
| 609 |
|
| 610 | get_futex_key_refs(key);
|
| 611 |
|
| 612 | out:
|
| 613 | unlock_page(page_head);
|
| 614 | put_page(page_head);
|
| 615 | return err;
|
| 616 | }
|
| 617 |
|
| 618 | static inline void put_futex_key(union futex_key *key)
|
| 619 | {
|
| 620 | drop_futex_key_refs(key);
|
| 621 | }
|
| 622 |
|
| 623 | |
| 624 | * fault_in_user_writeable() - Fault in user address and verify RW access
|
| 625 | * @uaddr: pointer to faulting user space address
|
| 626 | *
|
| 627 | * Slow path to fixup the fault we just took in the atomic write
|
| 628 | * access to @uaddr.
|
| 629 | *
|
| 630 | * We have no generic implementation of a non-destructive write to the
|
| 631 | * user address. We know that we faulted in the atomic pagefault
|
| 632 | * disabled section so we can as well avoid the #PF overhead by
|
| 633 | * calling get_user_pages() right away.
|
| 634 |
|
| 635 | static int fault_in_user_writeable(u32 __user *uaddr)
|
| 636 | {
|
| 637 | struct mm_struct *mm = current->mm;
|
| 638 | int ret;
|
| 639 |
|
| 640 | down_read(&mm->mmap_sem);
|
| 641 | ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
|
| 642 | FAULT_FLAG_WRITE);
|
| 643 | up_read(&mm->mmap_sem);
|
| 644 |
|
| 645 | return ret < 0 ? ret : 0;
|
| 646 | }
|
| 647 |
|
| 648 | |
| 649 | * futex_top_waiter() - Return the highest priority waiter on a futex
|
| 650 | * @hb: the hash bucket the futex_q's reside in
|
| 651 | * @key: the futex key (to distinguish it from other futex futex_q's)
|
| 652 | *
|
| 653 | * Must be called with the hb lock held.
|
| 654 |
|
| 655 | static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
|
| 656 | union futex_key *key)
|
| 657 | {
|
| 658 | struct futex_q *this;
|
| 659 |
|
| 660 | plist_for_each_entry(this, &hb->chain, list) {
|
| 661 | if (match_futex(&this->key, key))
|
| 662 | return this;
|
| 663 | }
|
| 664 | return NULL;
|
| 665 | }
|
| 666 |
|
| 667 | static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
|
| 668 | u32 uval, u32 newval)
|
| 669 | {
|
| 670 | int ret;
|
| 671 |
|
| 672 | pagefault_disable();
|
| 673 | ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
|
| 674 | pagefault_enable();
|
| 675 |
|
| 676 | return ret;
|
| 677 | }
|
| 678 |
|
| 679 | static int get_futex_value_locked(u32 *dest, u32 __user *from)
|
| 680 | {
|
| 681 | int ret;
|
| 682 |
|
| 683 | pagefault_disable();
|
| 684 | ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
|
| 685 | pagefault_enable();
|
| 686 |
|
| 687 | return ret ? -EFAULT : 0;
|
| 688 | }
|
| 689 |
|
| 690 |
|
| 691 | |
| 692 | * PI code:
|
| 693 |
|
| 694 | static int refill_pi_state_cache(void)
|
| 695 | {
|
| 696 | struct futex_pi_state *pi_state;
|
| 697 |
|
| 698 | if (likely(current->pi_state_cache))
|
| 699 | return 0;
|
| 700 |
|
| 701 | pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
|
| 702 |
|
| 703 | if (!pi_state)
|
| 704 | return -ENOMEM;
|
| 705 |
|
| 706 | INIT_LIST_HEAD(&pi_state->list);
|
| 707 |
|
| 708 | pi_state->owner = NULL;
|
| 709 | atomic_set(&pi_state->refcount, 1);
|
| 710 | pi_state->key = FUTEX_KEY_INIT;
|
| 711 |
|
| 712 | current->pi_state_cache = pi_state;
|
| 713 |
|
| 714 | return 0;
|
| 715 | }
|
| 716 |
|
| 717 | static struct futex_pi_state * alloc_pi_state(void)
|
| 718 | {
|
| 719 | struct futex_pi_state *pi_state = current->pi_state_cache;
|
| 720 |
|
| 721 | WARN_ON(!pi_state);
|
| 722 | current->pi_state_cache = NULL;
|
| 723 |
|
| 724 | return pi_state;
|
| 725 | }
|
| 726 |
|
| 727 | |
| 728 | * Must be called with the hb lock held.
|
| 729 |
|
| 730 | static void free_pi_state(struct futex_pi_state *pi_state)
|
| 731 | {
|
| 732 | if (!pi_state)
|
| 733 | return;
|
| 734 |
|
| 735 | if (!atomic_dec_and_test(&pi_state->refcount))
|
| 736 | return;
|
| 737 |
|
| 738 | |
| 739 | * If pi_state->owner is NULL, the owner is most probably dying
|
| 740 | * and has cleaned up the pi_state already
|
| 741 |
|
| 742 | if (pi_state->owner) {
|
| 743 | raw_spin_lock_irq(&pi_state->owner->pi_lock);
|
| 744 | list_del_init(&pi_state->list);
|
| 745 | raw_spin_unlock_irq(&pi_state->owner->pi_lock);
|
| 746 |
|
| 747 | rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
|
| 748 | }
|
| 749 |
|
| 750 | if (current->pi_state_cache)
|
| 751 | kfree(pi_state);
|
| 752 | else {
|
| 753 | |
| 754 | * pi_state->list is already empty.
|
| 755 | * clear pi_state->owner.
|
| 756 | * refcount is at 0 - put it back to 1.
|
| 757 |
|
| 758 | pi_state->owner = NULL;
|
| 759 | atomic_set(&pi_state->refcount, 1);
|
| 760 | current->pi_state_cache = pi_state;
|
| 761 | }
|
| 762 | }
|
| 763 |
|
| 764 | |
| 765 | * Look up the task based on what TID userspace gave us.
|
| 766 | * We dont trust it.
|
| 767 |
|
| 768 | static struct task_struct * futex_find_get_task(pid_t pid)
|
| 769 | {
|
| 770 | struct task_struct *p;
|
| 771 |
|
| 772 | rcu_read_lock();
|
| 773 | p = find_task_by_vpid(pid);
|
| 774 | if (p)
|
| 775 | get_task_struct(p);
|
| 776 |
|
| 777 | rcu_read_unlock();
|
| 778 |
|
| 779 | return p;
|
| 780 | }
|
| 781 |
|
| 782 | |
| 783 | * This task is holding PI mutexes at exit time => bad.
|
| 784 | * Kernel cleans up PI-state, but userspace is likely hosed.
|
| 785 | * (Robust-futex cleanup is separate and might save the day for userspace.)
|
| 786 |
|
| 787 | void exit_pi_state_list(struct task_struct *curr)
|
| 788 | {
|
| 789 | struct list_head *next, *head = &curr->pi_state_list;
|
| 790 | struct futex_pi_state *pi_state;
|
| 791 | struct futex_hash_bucket *hb;
|
| 792 | union futex_key key = FUTEX_KEY_INIT;
|
| 793 |
|
| 794 | if (!futex_cmpxchg_enabled)
|
| 795 | return;
|
| 796 | |
| 797 | * We are a ZOMBIE and nobody can enqueue itself on
|
| 798 | * pi_state_list anymore, but we have to be careful
|
| 799 | * versus waiters unqueueing themselves:
|
| 800 |
|
| 801 | raw_spin_lock_irq(&curr->pi_lock);
|
| 802 | while (!list_empty(head)) {
|
| 803 |
|
| 804 | next = head->next;
|
| 805 | pi_state = list_entry(next, struct futex_pi_state, list);
|
| 806 | key = pi_state->key;
|
| 807 | hb = hash_futex(&key);
|
| 808 | raw_spin_unlock_irq(&curr->pi_lock);
|
| 809 |
|
| 810 | spin_lock(&hb->lock);
|
| 811 |
|
| 812 | raw_spin_lock_irq(&curr->pi_lock);
|
| 813 | |
| 814 | * We dropped the pi-lock, so re-check whether this
|
| 815 | * task still owns the PI-state:
|
| 816 |
|
| 817 | if (head->next != next) {
|
| 818 | spin_unlock(&hb->lock);
|
| 819 | continue;
|
| 820 | }
|
| 821 |
|
| 822 | WARN_ON(pi_state->owner != curr);
|
| 823 | WARN_ON(list_empty(&pi_state->list));
|
| 824 | list_del_init(&pi_state->list);
|
| 825 | pi_state->owner = NULL;
|
| 826 | raw_spin_unlock_irq(&curr->pi_lock);
|
| 827 |
|
| 828 | rt_mutex_unlock(&pi_state->pi_mutex);
|
| 829 |
|
| 830 | spin_unlock(&hb->lock);
|
| 831 |
|
| 832 | raw_spin_lock_irq(&curr->pi_lock);
|
| 833 | }
|
| 834 | raw_spin_unlock_irq(&curr->pi_lock);
|
| 835 | }
|
| 836 |
|
| 837 | |
| 838 | * We need to check the following states:
|
| 839 | *
|
| 840 | * Waiter | pi_state | pi->owner | uTID | uODIED | ?
|
| 841 | *
|
| 842 | * [1] NULL | --- | --- | 0 | 0/1 | Valid
|
| 843 | * [2] NULL | --- | --- | >0 | 0/1 | Valid
|
| 844 | *
|
| 845 | * [3] Found | NULL | -- | Any | 0/1 | Invalid
|
| 846 | *
|
| 847 | * [4] Found | Found | NULL | 0 | 1 | Valid
|
| 848 | * [5] Found | Found | NULL | >0 | 1 | Invalid
|
| 849 | *
|
| 850 | * [6] Found | Found | task | 0 | 1 | Valid
|
| 851 | *
|
| 852 | * [7] Found | Found | NULL | Any | 0 | Invalid
|
| 853 | *
|
| 854 | * [8] Found | Found | task | ==taskTID | 0/1 | Valid
|
| 855 | * [9] Found | Found | task | 0 | 0 | Invalid
|
| 856 | * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
|
| 857 | *
|
| 858 | * [1] Indicates that the kernel can acquire the futex atomically. We
|
| 859 | * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
|
| 860 | *
|
| 861 | * [2] Valid, if TID does not belong to a kernel thread. If no matching
|
| 862 | * thread is found then it indicates that the owner TID has died.
|
| 863 | *
|
| 864 | * [3] Invalid. The waiter is queued on a non PI futex
|
| 865 | *
|
| 866 | * [4] Valid state after exit_robust_list(), which sets the user space
|
| 867 | * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
|
| 868 | *
|
| 869 | * [5] The user space value got manipulated between exit_robust_list()
|
| 870 | * and exit_pi_state_list()
|
| 871 | *
|
| 872 | * [6] Valid state after exit_pi_state_list() which sets the new owner in
|
| 873 | * the pi_state but cannot access the user space value.
|
| 874 | *
|
| 875 | * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
|
| 876 | *
|
| 877 | * [8] Owner and user space value match
|
| 878 | *
|
| 879 | * [9] There is no transient state which sets the user space TID to 0
|
| 880 | * except exit_robust_list(), but this is indicated by the
|
| 881 | * FUTEX_OWNER_DIED bit. See [4]
|
| 882 | *
|
| 883 | * [10] There is no transient state which leaves owner and user space
|
| 884 | * TID out of sync.
|
| 885 |
|
| 886 |
|
| 887 | |
| 888 | * Validate that the existing waiter has a pi_state and sanity check
|
| 889 | * the pi_state against the user space value. If correct, attach to
|
| 890 | * it.
|
| 891 |
|
| 892 | static int attach_to_pi_state(u32 uval, struct futex_pi_state *pi_state,
|
| 893 | struct futex_pi_state **ps)
|
| 894 | {
|
| 895 | pid_t pid = uval & FUTEX_TID_MASK;
|
| 896 |
|
| 897 | |
| 898 | * Userspace might have messed up non-PI and PI futexes [3]
|
| 899 |
|
| 900 | if (unlikely(!pi_state))
|
| 901 | return -EINVAL;
|
| 902 |
|
| 903 | WARN_ON(!atomic_read(&pi_state->refcount));
|
| 904 |
|
| 905 | |
| 906 | * Handle the owner died case:
|
| 907 |
|
| 908 | if (uval & FUTEX_OWNER_DIED) {
|
| 909 | |
| 910 | * exit_pi_state_list sets owner to NULL and wakes the
|
| 911 | * topmost waiter. The task which acquires the
|
| 912 | * pi_state->rt_mutex will fixup owner.
|
| 913 |
|
| 914 | if (!pi_state->owner) {
|
| 915 | |
| 916 | * No pi state owner, but the user space TID
|
| 917 | * is not 0. Inconsistent state. [5]
|
| 918 |
|
| 919 | if (pid)
|
| 920 | return -EINVAL;
|
| 921 | |
| 922 | * Take a ref on the state and return success. [4]
|
| 923 |
|
| 924 | goto out_state;
|
| 925 | }
|
| 926 |
|
| 927 | |
| 928 | * If TID is 0, then either the dying owner has not
|
| 929 | * yet executed exit_pi_state_list() or some waiter
|
| 930 | * acquired the rtmutex in the pi state, but did not
|
| 931 | * yet fixup the TID in user space.
|
| 932 | *
|
| 933 | * Take a ref on the state and return success. [6]
|
| 934 |
|
| 935 | if (!pid)
|
| 936 | goto out_state;
|
| 937 | } else {
|
| 938 | |
| 939 | * If the owner died bit is not set, then the pi_state
|
| 940 | * must have an owner. [7]
|
| 941 |
|
| 942 | if (!pi_state->owner)
|
| 943 | return -EINVAL;
|
| 944 | }
|
| 945 |
|
| 946 | |
| 947 | * Bail out if user space manipulated the futex value. If pi
|
| 948 | * state exists then the owner TID must be the same as the
|
| 949 | * user space TID. [9/10]
|
| 950 |
|
| 951 | if (pid != task_pid_vnr(pi_state->owner))
|
| 952 | return -EINVAL;
|
| 953 | out_state:
|
| 954 | atomic_inc(&pi_state->refcount);
|
| 955 | *ps = pi_state;
|
| 956 | return 0;
|
| 957 | }
|
| 958 |
|
| 959 | |
| 960 | * Lookup the task for the TID provided from user space and attach to
|
| 961 | * it after doing proper sanity checks.
|
| 962 |
|
| 963 | static int attach_to_pi_owner(u32 uval, union futex_key *key,
|
| 964 | struct futex_pi_state **ps)
|
| 965 | {
|
| 966 | pid_t pid = uval & FUTEX_TID_MASK;
|
| 967 | struct futex_pi_state *pi_state;
|
| 968 | struct task_struct *p;
|
| 969 |
|
| 970 | |
| 971 | * We are the first waiter - try to look up the real owner and attach
|
| 972 | * the new pi_state to it, but bail out when TID = 0 [1]
|
| 973 |
|
| 974 | if (!pid)
|
| 975 | return -ESRCH;
|
| 976 | p = futex_find_get_task(pid);
|
| 977 | if (!p)
|
| 978 | return -ESRCH;
|
| 979 |
|
| 980 | if (unlikely(p->flags & PF_KTHREAD)) {
|
| 981 | put_task_struct(p);
|
| 982 | return -EPERM;
|
| 983 | }
|
| 984 |
|
| 985 | |
| 986 | * We need to look at the task state flags to figure out,
|
| 987 | * whether the task is exiting. To protect against the do_exit
|
| 988 | * change of the task flags, we do this protected by
|
| 989 | * p->pi_lock:
|
| 990 |
|
| 991 | raw_spin_lock_irq(&p->pi_lock);
|
| 992 | if (unlikely(p->flags & PF_EXITING)) {
|
| 993 | |
| 994 | * The task is on the way out. When PF_EXITPIDONE is
|
| 995 | * set, we know that the task has finished the
|
| 996 | * cleanup:
|
| 997 |
|
| 998 | int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
|
| 999 |
|
| 1000 | raw_spin_unlock_irq(&p->pi_lock);
|
| 1001 | put_task_struct(p);
|
| 1002 | return ret;
|
| 1003 | }
|
| 1004 |
|
| 1005 | |
| 1006 | * No existing pi state. First waiter. [2]
|
| 1007 |
|
| 1008 | pi_state = alloc_pi_state();
|
| 1009 |
|
| 1010 | |
| 1011 | * Initialize the pi_mutex in locked state and make @p
|
| 1012 | * the owner of it:
|
| 1013 |
|
| 1014 | rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
|
| 1015 |
|
| 1016 |
|
| 1017 | pi_state->key = *key;
|
| 1018 |
|
| 1019 | WARN_ON(!list_empty(&pi_state->list));
|
| 1020 | list_add(&pi_state->list, &p->pi_state_list);
|
| 1021 | pi_state->owner = p;
|
| 1022 | raw_spin_unlock_irq(&p->pi_lock);
|
| 1023 |
|
| 1024 | put_task_struct(p);
|
| 1025 |
|
| 1026 | *ps = pi_state;
|
| 1027 |
|
| 1028 | return 0;
|
| 1029 | }
|
| 1030 |
|
| 1031 | static int lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
|
| 1032 | union futex_key *key, struct futex_pi_state **ps)
|
| 1033 | {
|
| 1034 | struct futex_q *match = futex_top_waiter(hb, key);
|
| 1035 |
|
| 1036 | |
| 1037 | * If there is a waiter on that futex, validate it and
|
| 1038 | * attach to the pi_state when the validation succeeds.
|
| 1039 |
|
| 1040 | if (match)
|
| 1041 | return attach_to_pi_state(uval, match->pi_state, ps);
|
| 1042 |
|
| 1043 | |
| 1044 | * We are the first waiter - try to look up the owner based on
|
| 1045 | * @uval and attach to it.
|
| 1046 |
|
| 1047 | return attach_to_pi_owner(uval, key, ps);
|
| 1048 | }
|
| 1049 |
|
| 1050 | static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
|
| 1051 | {
|
| 1052 | u32 uninitialized_var(curval);
|
| 1053 |
|
| 1054 | if (unlikely(should_fail_futex(true)))
|
| 1055 | return -EFAULT;
|
| 1056 |
|
| 1057 | if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
|
| 1058 | return -EFAULT;
|
| 1059 |
|
| 1060 |
|
| 1061 | return curval != uval ? -EAGAIN : 0;
|
| 1062 | }
|
| 1063 |
|
| 1064 | |
| 1065 | * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
|
| 1066 | * @uaddr: the pi futex user address
|
| 1067 | * @hb: the pi futex hash bucket
|
| 1068 | * @key: the futex key associated with uaddr and hb
|
| 1069 | * @ps: the pi_state pointer where we store the result of the
|
| 1070 | * lookup
|
| 1071 | * @task: the task to perform the atomic lock work for. This will
|
| 1072 | * be "current" except in the case of requeue pi.
|
| 1073 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
|
| 1074 | *
|
| 1075 | * Return:
|
| 1076 | * 0 - ready to wait;
|
| 1077 | * 1 - acquired the lock;
|
| 1078 | * <0 - error
|
| 1079 | *
|
| 1080 | * The hb->lock and futex_key refs shall be held by the caller.
|
| 1081 |
|
| 1082 | static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
|
| 1083 | union futex_key *key,
|
| 1084 | struct futex_pi_state **ps,
|
| 1085 | struct task_struct *task, int set_waiters)
|
| 1086 | {
|
| 1087 | u32 uval, newval, vpid = task_pid_vnr(task);
|
| 1088 | struct futex_q *match;
|
| 1089 | int ret;
|
| 1090 |
|
| 1091 | |
| 1092 | * Read the user space value first so we can validate a few
|
| 1093 | * things before proceeding further.
|
| 1094 |
|
| 1095 | if (get_futex_value_locked(&uval, uaddr))
|
| 1096 | return -EFAULT;
|
| 1097 |
|
| 1098 | if (unlikely(should_fail_futex(true)))
|
| 1099 | return -EFAULT;
|
| 1100 |
|
| 1101 | |
| 1102 | * Detect deadlocks.
|
| 1103 |
|
| 1104 | if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
|
| 1105 | return -EDEADLK;
|
| 1106 |
|
| 1107 | if ((unlikely(should_fail_futex(true))))
|
| 1108 | return -EDEADLK;
|
| 1109 |
|
| 1110 | |
| 1111 | * Lookup existing state first. If it exists, try to attach to
|
| 1112 | * its pi_state.
|
| 1113 |
|
| 1114 | match = futex_top_waiter(hb, key);
|
| 1115 | if (match)
|
| 1116 | return attach_to_pi_state(uval, match->pi_state, ps);
|
| 1117 |
|
| 1118 | |
| 1119 | * No waiter and user TID is 0. We are here because the
|
| 1120 | * waiters or the owner died bit is set or called from
|
| 1121 | * requeue_cmp_pi or for whatever reason something took the
|
| 1122 | * syscall.
|
| 1123 |
|
| 1124 | if (!(uval & FUTEX_TID_MASK)) {
|
| 1125 | |
| 1126 | * We take over the futex. No other waiters and the user space
|
| 1127 | * TID is 0. We preserve the owner died bit.
|
| 1128 |
|
| 1129 | newval = uval & FUTEX_OWNER_DIED;
|
| 1130 | newval |= vpid;
|
| 1131 |
|
| 1132 |
|
| 1133 | if (set_waiters)
|
| 1134 | newval |= FUTEX_WAITERS;
|
| 1135 |
|
| 1136 | ret = lock_pi_update_atomic(uaddr, uval, newval);
|
| 1137 |
|
| 1138 | return ret < 0 ? ret : 1;
|
| 1139 | }
|
| 1140 |
|
| 1141 | |
| 1142 | * First waiter. Set the waiters bit before attaching ourself to
|
| 1143 | * the owner. If owner tries to unlock, it will be forced into
|
| 1144 | * the kernel and blocked on hb->lock.
|
| 1145 |
|
| 1146 | newval = uval | FUTEX_WAITERS;
|
| 1147 | ret = lock_pi_update_atomic(uaddr, uval, newval);
|
| 1148 | if (ret)
|
| 1149 | return ret;
|
| 1150 | |
| 1151 | * If the update of the user space value succeeded, we try to
|
| 1152 | * attach to the owner. If that fails, no harm done, we only
|
| 1153 | * set the FUTEX_WAITERS bit in the user space variable.
|
| 1154 |
|
| 1155 | return attach_to_pi_owner(uval, key, ps);
|
| 1156 | }
|
| 1157 |
|
| 1158 | |
| 1159 | * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
|
| 1160 | * @q: The futex_q to unqueue
|
| 1161 | *
|
| 1162 | * The q->lock_ptr must not be NULL and must be held by the caller.
|
| 1163 |
|
| 1164 | static void __unqueue_futex(struct futex_q *q)
|
| 1165 | {
|
| 1166 | struct futex_hash_bucket *hb;
|
| 1167 |
|
| 1168 | if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
|
| 1169 | || WARN_ON(plist_node_empty(&q->list)))
|
| 1170 | return;
|
| 1171 |
|
| 1172 | hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
|
| 1173 | plist_del(&q->list, &hb->chain);
|
| 1174 | hb_waiters_dec(hb);
|
| 1175 | }
|
| 1176 |
|
| 1177 | |
| 1178 | * The hash bucket lock must be held when this is called.
|
| 1179 | * Afterwards, the futex_q must not be accessed. Callers
|
| 1180 | * must ensure to later call wake_up_q() for the actual
|
| 1181 | * wakeups to occur.
|
| 1182 |
|
| 1183 | static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
|
| 1184 | {
|
| 1185 | struct task_struct *p = q->task;
|
| 1186 |
|
| 1187 | if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
|
| 1188 | return;
|
| 1189 |
|
| 1190 | |
| 1191 | * Queue the task for later wakeup for after we've released
|
| 1192 | * the hb->lock. wake_q_add() grabs reference to p.
|
| 1193 |
|
| 1194 | wake_q_add(wake_q, p);
|
| 1195 | __unqueue_futex(q);
|
| 1196 | |
| 1197 | * The waiting task can free the futex_q as soon as
|
| 1198 | * q->lock_ptr = NULL is written, without taking any locks. A
|
| 1199 | * memory barrier is required here to prevent the following
|
| 1200 | * store to lock_ptr from getting ahead of the plist_del.
|
| 1201 |
|
| 1202 | smp_wmb();
|
| 1203 | q->lock_ptr = NULL;
|
| 1204 | }
|
| 1205 |
|
| 1206 | static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this,
|
| 1207 | struct futex_hash_bucket *hb)
|
| 1208 | {
|
| 1209 | struct task_struct *new_owner;
|
| 1210 | struct futex_pi_state *pi_state = this->pi_state;
|
| 1211 | u32 uninitialized_var(curval), newval;
|
| 1212 | WAKE_Q(wake_q);
|
| 1213 | bool deboost;
|
| 1214 | int ret = 0;
|
| 1215 |
|
| 1216 | if (!pi_state)
|
| 1217 | return -EINVAL;
|
| 1218 |
|
| 1219 | |
| 1220 | * If current does not own the pi_state then the futex is
|
| 1221 | * inconsistent and user space fiddled with the futex value.
|
| 1222 |
|
| 1223 | if (pi_state->owner != current)
|
| 1224 | return -EINVAL;
|
| 1225 |
|
| 1226 | raw_spin_lock(&pi_state->pi_mutex.wait_lock);
|
| 1227 | new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
|
| 1228 |
|
| 1229 | |
| 1230 | * It is possible that the next waiter (the one that brought
|
| 1231 | * this owner to the kernel) timed out and is no longer
|
| 1232 | * waiting on the lock.
|
| 1233 |
|
| 1234 | if (!new_owner)
|
| 1235 | new_owner = this->task;
|
| 1236 |
|
| 1237 | |
| 1238 | * We pass it to the next owner. The WAITERS bit is always
|
| 1239 | * kept enabled while there is PI state around. We cleanup the
|
| 1240 | * owner died bit, because we are the owner.
|
| 1241 |
|
| 1242 | newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
|
| 1243 |
|
| 1244 | if (unlikely(should_fail_futex(true)))
|
| 1245 | ret = -EFAULT;
|
| 1246 |
|
| 1247 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
|
| 1248 | ret = -EFAULT;
|
| 1249 | else if (curval != uval)
|
| 1250 | ret = -EINVAL;
|
| 1251 | if (ret) {
|
| 1252 | raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
|
| 1253 | return ret;
|
| 1254 | }
|
| 1255 |
|
| 1256 | raw_spin_lock_irq(&pi_state->owner->pi_lock);
|
| 1257 | WARN_ON(list_empty(&pi_state->list));
|
| 1258 | list_del_init(&pi_state->list);
|
| 1259 | raw_spin_unlock_irq(&pi_state->owner->pi_lock);
|
| 1260 |
|
| 1261 | raw_spin_lock_irq(&new_owner->pi_lock);
|
| 1262 | WARN_ON(!list_empty(&pi_state->list));
|
| 1263 | list_add(&pi_state->list, &new_owner->pi_state_list);
|
| 1264 | pi_state->owner = new_owner;
|
| 1265 | raw_spin_unlock_irq(&new_owner->pi_lock);
|
| 1266 |
|
| 1267 | raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
|
| 1268 |
|
| 1269 | deboost = rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
|
| 1270 |
|
| 1271 | |
| 1272 | * First unlock HB so the waiter does not spin on it once he got woken
|
| 1273 | * up. Second wake up the waiter before the priority is adjusted. If we
|
| 1274 | * deboost first (and lose our higher priority), then the task might get
|
| 1275 | * scheduled away before the wake up can take place.
|
| 1276 |
|
| 1277 | spin_unlock(&hb->lock);
|
| 1278 | wake_up_q(&wake_q);
|
| 1279 | if (deboost)
|
| 1280 | rt_mutex_adjust_prio(current);
|
| 1281 |
|
| 1282 | return 0;
|
| 1283 | }
|
| 1284 |
|
| 1285 | |
| 1286 | * Express the locking dependencies for lockdep:
|
| 1287 |
|
| 1288 | static inline void
|
| 1289 | double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
|
| 1290 | {
|
| 1291 | if (hb1 <= hb2) {
|
| 1292 | spin_lock(&hb1->lock);
|
| 1293 | if (hb1 < hb2)
|
| 1294 | spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
|
| 1295 | } else {
|
| 1296 | spin_lock(&hb2->lock);
|
| 1297 | spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
|
| 1298 | }
|
| 1299 | }
|
| 1300 |
|
| 1301 | static inline void
|
| 1302 | double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
|
| 1303 | {
|
| 1304 | spin_unlock(&hb1->lock);
|
| 1305 | if (hb1 != hb2)
|
| 1306 | spin_unlock(&hb2->lock);
|
| 1307 | }
|
| 1308 |
|
| 1309 | |
| 1310 | * Wake up waiters matching bitset queued on this futex (uaddr).
|
| 1311 |
|
| 1312 | static int
|
| 1313 | futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
|
| 1314 | {
|
| 1315 | struct futex_hash_bucket *hb;
|
| 1316 | struct futex_q *this, *next;
|
| 1317 | union futex_key key = FUTEX_KEY_INIT;
|
| 1318 | int ret;
|
| 1319 | WAKE_Q(wake_q);
|
| 1320 |
|
| 1321 | if (!bitset)
|
| 1322 | return -EINVAL;
|
| 1323 |
|
| 1324 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
|
| 1325 | if (unlikely(ret != 0))
|
| 1326 | goto out;
|
| 1327 |
|
| 1328 | hb = hash_futex(&key);
|
| 1329 |
|
| 1330 |
|
| 1331 | if (!hb_waiters_pending(hb))
|
| 1332 | goto out_put_key;
|
| 1333 |
|
| 1334 | spin_lock(&hb->lock);
|
| 1335 |
|
| 1336 | plist_for_each_entry_safe(this, next, &hb->chain, list) {
|
| 1337 | if (match_futex (&this->key, &key)) {
|
| 1338 | if (this->pi_state || this->rt_waiter) {
|
| 1339 | ret = -EINVAL;
|
| 1340 | break;
|
| 1341 | }
|
| 1342 |
|
| 1343 |
|
| 1344 | if (!(this->bitset & bitset))
|
| 1345 | continue;
|
| 1346 |
|
| 1347 | mark_wake_futex(&wake_q, this);
|
| 1348 | if (++ret >= nr_wake)
|
| 1349 | break;
|
| 1350 | }
|
| 1351 | }
|
| 1352 |
|
| 1353 | spin_unlock(&hb->lock);
|
| 1354 | wake_up_q(&wake_q);
|
| 1355 | out_put_key:
|
| 1356 | put_futex_key(&key);
|
| 1357 | out:
|
| 1358 | return ret;
|
| 1359 | }
|
| 1360 |
|
| 1361 | |
| 1362 | * Wake up all waiters hashed on the physical page that is mapped
|
| 1363 | * to this virtual address:
|
| 1364 |
|
| 1365 | static int
|
| 1366 | futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
|
| 1367 | int nr_wake, int nr_wake2, int op)
|
| 1368 | {
|
| 1369 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
|
| 1370 | struct futex_hash_bucket *hb1, *hb2;
|
| 1371 | struct futex_q *this, *next;
|
| 1372 | int ret, op_ret;
|
| 1373 | WAKE_Q(wake_q);
|
| 1374 |
|
| 1375 | retry:
|
| 1376 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
|
| 1377 | if (unlikely(ret != 0))
|
| 1378 | goto out;
|
| 1379 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
|
| 1380 | if (unlikely(ret != 0))
|
| 1381 | goto out_put_key1;
|
| 1382 |
|
| 1383 | hb1 = hash_futex(&key1);
|
| 1384 | hb2 = hash_futex(&key2);
|
| 1385 |
|
| 1386 | retry_private:
|
| 1387 | double_lock_hb(hb1, hb2);
|
| 1388 | op_ret = futex_atomic_op_inuser(op, uaddr2);
|
| 1389 | if (unlikely(op_ret < 0)) {
|
| 1390 |
|
| 1391 | double_unlock_hb(hb1, hb2);
|
| 1392 |
|
| 1393 | #ifndef CONFIG_MMU
|
| 1394 | |
| 1395 | * we don't get EFAULT from MMU faults if we don't have an MMU,
|
| 1396 | * but we might get them from range checking
|
| 1397 |
|
| 1398 | ret = op_ret;
|
| 1399 | goto out_put_keys;
|
| 1400 | #endif
|
| 1401 |
|
| 1402 | if (unlikely(op_ret != -EFAULT)) {
|
| 1403 | ret = op_ret;
|
| 1404 | goto out_put_keys;
|
| 1405 | }
|
| 1406 |
|
| 1407 | ret = fault_in_user_writeable(uaddr2);
|
| 1408 | if (ret)
|
| 1409 | goto out_put_keys;
|
| 1410 |
|
| 1411 | if (!(flags & FLAGS_SHARED))
|
| 1412 | goto retry_private;
|
| 1413 |
|
| 1414 | put_futex_key(&key2);
|
| 1415 | put_futex_key(&key1);
|
| 1416 | goto retry;
|
| 1417 | }
|
| 1418 |
|
| 1419 | plist_for_each_entry_safe(this, next, &hb1->chain, list) {
|
| 1420 | if (match_futex (&this->key, &key1)) {
|
| 1421 | if (this->pi_state || this->rt_waiter) {
|
| 1422 | ret = -EINVAL;
|
| 1423 | goto out_unlock;
|
| 1424 | }
|
| 1425 | mark_wake_futex(&wake_q, this);
|
| 1426 | if (++ret >= nr_wake)
|
| 1427 | break;
|
| 1428 | }
|
| 1429 | }
|
| 1430 |
|
| 1431 | if (op_ret > 0) {
|
| 1432 | op_ret = 0;
|
| 1433 | plist_for_each_entry_safe(this, next, &hb2->chain, list) {
|
| 1434 | if (match_futex (&this->key, &key2)) {
|
| 1435 | if (this->pi_state || this->rt_waiter) {
|
| 1436 | ret = -EINVAL;
|
| 1437 | goto out_unlock;
|
| 1438 | }
|
| 1439 | mark_wake_futex(&wake_q, this);
|
| 1440 | if (++op_ret >= nr_wake2)
|
| 1441 | break;
|
| 1442 | }
|
| 1443 | }
|
| 1444 | ret += op_ret;
|
| 1445 | }
|
| 1446 |
|
| 1447 | out_unlock:
|
| 1448 | double_unlock_hb(hb1, hb2);
|
| 1449 | wake_up_q(&wake_q);
|
| 1450 | out_put_keys:
|
| 1451 | put_futex_key(&key2);
|
| 1452 | out_put_key1:
|
| 1453 | put_futex_key(&key1);
|
| 1454 | out:
|
| 1455 | return ret;
|
| 1456 | }
|
| 1457 |
|
| 1458 | |
| 1459 | * requeue_futex() - Requeue a futex_q from one hb to another
|
| 1460 | * @q: the futex_q to requeue
|
| 1461 | * @hb1: the source hash_bucket
|
| 1462 | * @hb2: the target hash_bucket
|
| 1463 | * @key2: the new key for the requeued futex_q
|
| 1464 |
|
| 1465 | static inline
|
| 1466 | void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
|
| 1467 | struct futex_hash_bucket *hb2, union futex_key *key2)
|
| 1468 | {
|
| 1469 |
|
| 1470 | |
| 1471 | * If key1 and key2 hash to the same bucket, no need to
|
| 1472 | * requeue.
|
| 1473 |
|
| 1474 | if (likely(&hb1->chain != &hb2->chain)) {
|
| 1475 | plist_del(&q->list, &hb1->chain);
|
| 1476 | hb_waiters_dec(hb1);
|
| 1477 | plist_add(&q->list, &hb2->chain);
|
| 1478 | hb_waiters_inc(hb2);
|
| 1479 | q->lock_ptr = &hb2->lock;
|
| 1480 | }
|
| 1481 | get_futex_key_refs(key2);
|
| 1482 | q->key = *key2;
|
| 1483 | }
|
| 1484 |
|
| 1485 | |
| 1486 | * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
|
| 1487 | * @q: the futex_q
|
| 1488 | * @key: the key of the requeue target futex
|
| 1489 | * @hb: the hash_bucket of the requeue target futex
|
| 1490 | *
|
| 1491 | * During futex_requeue, with requeue_pi=1, it is possible to acquire the
|
| 1492 | * target futex if it is uncontended or via a lock steal. Set the futex_q key
|
| 1493 | * to the requeue target futex so the waiter can detect the wakeup on the right
|
| 1494 | * futex, but remove it from the hb and NULL the rt_waiter so it can detect
|
| 1495 | * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
|
| 1496 | * to protect access to the pi_state to fixup the owner later. Must be called
|
| 1497 | * with both q->lock_ptr and hb->lock held.
|
| 1498 |
|
| 1499 | static inline
|
| 1500 | void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
|
| 1501 | struct futex_hash_bucket *hb)
|
| 1502 | {
|
| 1503 | get_futex_key_refs(key);
|
| 1504 | q->key = *key;
|
| 1505 |
|
| 1506 | __unqueue_futex(q);
|
| 1507 |
|
| 1508 | WARN_ON(!q->rt_waiter);
|
| 1509 | q->rt_waiter = NULL;
|
| 1510 |
|
| 1511 | q->lock_ptr = &hb->lock;
|
| 1512 |
|
| 1513 | wake_up_state(q->task, TASK_NORMAL);
|
| 1514 | }
|
| 1515 |
|
| 1516 | |
| 1517 | * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
|
| 1518 | * @pifutex: the user address of the to futex
|
| 1519 | * @hb1: the from futex hash bucket, must be locked by the caller
|
| 1520 | * @hb2: the to futex hash bucket, must be locked by the caller
|
| 1521 | * @key1: the from futex key
|
| 1522 | * @key2: the to futex key
|
| 1523 | * @ps: address to store the pi_state pointer
|
| 1524 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
|
| 1525 | *
|
| 1526 | * Try and get the lock on behalf of the top waiter if we can do it atomically.
|
| 1527 | * Wake the top waiter if we succeed. If the caller specified set_waiters,
|
| 1528 | * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
|
| 1529 | * hb1 and hb2 must be held by the caller.
|
| 1530 | *
|
| 1531 | * Return:
|
| 1532 | * 0 - failed to acquire the lock atomically;
|
| 1533 | * >0 - acquired the lock, return value is vpid of the top_waiter
|
| 1534 | * <0 - error
|
| 1535 |
|
| 1536 | static int futex_proxy_trylock_atomic(u32 __user *pifutex,
|
| 1537 | struct futex_hash_bucket *hb1,
|
| 1538 | struct futex_hash_bucket *hb2,
|
| 1539 | union futex_key *key1, union futex_key *key2,
|
| 1540 | struct futex_pi_state **ps, int set_waiters)
|
| 1541 | {
|
| 1542 | struct futex_q *top_waiter = NULL;
|
| 1543 | u32 curval;
|
| 1544 | int ret, vpid;
|
| 1545 |
|
| 1546 | if (get_futex_value_locked(&curval, pifutex))
|
| 1547 | return -EFAULT;
|
| 1548 |
|
| 1549 | if (unlikely(should_fail_futex(true)))
|
| 1550 | return -EFAULT;
|
| 1551 |
|
| 1552 | |
| 1553 | * Find the top_waiter and determine if there are additional waiters.
|
| 1554 | * If the caller intends to requeue more than 1 waiter to pifutex,
|
| 1555 | * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
|
| 1556 | * as we have means to handle the possible fault. If not, don't set
|
| 1557 | * the bit unecessarily as it will force the subsequent unlock to enter
|
| 1558 | * the kernel.
|
| 1559 |
|
| 1560 | top_waiter = futex_top_waiter(hb1, key1);
|
| 1561 |
|
| 1562 |
|
| 1563 | if (!top_waiter)
|
| 1564 | return 0;
|
| 1565 |
|
| 1566 |
|
| 1567 | if (!match_futex(top_waiter->requeue_pi_key, key2))
|
| 1568 | return -EINVAL;
|
| 1569 |
|
| 1570 | |
| 1571 | * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
|
| 1572 | * the contended case or if set_waiters is 1. The pi_state is returned
|
| 1573 | * in ps in contended cases.
|
| 1574 |
|
| 1575 | vpid = task_pid_vnr(top_waiter->task);
|
| 1576 | ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
|
| 1577 | set_waiters);
|
| 1578 | if (ret == 1) {
|
| 1579 | requeue_pi_wake_futex(top_waiter, key2, hb2);
|
| 1580 | return vpid;
|
| 1581 | }
|
| 1582 | return ret;
|
| 1583 | }
|
| 1584 |
|
| 1585 | |
| 1586 | * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
|
| 1587 | * @uaddr1: source futex user address
|
| 1588 | * @flags: futex flags (FLAGS_SHARED, etc.)
|
| 1589 | * @uaddr2: target futex user address
|
| 1590 | * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
|
| 1591 | * @nr_requeue: number of waiters to requeue (0-INT_MAX)
|
| 1592 | * @cmpval: @uaddr1 expected value (or %NULL)
|
| 1593 | * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
|
| 1594 | * pi futex (pi to pi requeue is not supported)
|
| 1595 | *
|
| 1596 | * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
|
| 1597 | * uaddr2 atomically on behalf of the top waiter.
|
| 1598 | *
|
| 1599 | * Return:
|
| 1600 | * >=0 - on success, the number of tasks requeued or woken;
|
| 1601 | * <0 - on error
|
| 1602 |
|
| 1603 | static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
|
| 1604 | u32 __user *uaddr2, int nr_wake, int nr_requeue,
|
| 1605 | u32 *cmpval, int requeue_pi)
|
| 1606 | {
|
| 1607 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
|
| 1608 | int drop_count = 0, task_count = 0, ret;
|
| 1609 | struct futex_pi_state *pi_state = NULL;
|
| 1610 | struct futex_hash_bucket *hb1, *hb2;
|
| 1611 | struct futex_q *this, *next;
|
| 1612 | WAKE_Q(wake_q);
|
| 1613 |
|
| 1614 | if (requeue_pi) {
|
| 1615 | |
| 1616 | * Requeue PI only works on two distinct uaddrs. This
|
| 1617 | * check is only valid for private futexes. See below.
|
| 1618 |
|
| 1619 | if (uaddr1 == uaddr2)
|
| 1620 | return -EINVAL;
|
| 1621 |
|
| 1622 | |
| 1623 | * requeue_pi requires a pi_state, try to allocate it now
|
| 1624 | * without any locks in case it fails.
|
| 1625 |
|
| 1626 | if (refill_pi_state_cache())
|
| 1627 | return -ENOMEM;
|
| 1628 | |
| 1629 | * requeue_pi must wake as many tasks as it can, up to nr_wake
|
| 1630 | * + nr_requeue, since it acquires the rt_mutex prior to
|
| 1631 | * returning to userspace, so as to not leave the rt_mutex with
|
| 1632 | * waiters and no owner. However, second and third wake-ups
|
| 1633 | * cannot be predicted as they involve race conditions with the
|
| 1634 | * first wake and a fault while looking up the pi_state. Both
|
| 1635 | * pthread_cond_signal() and pthread_cond_broadcast() should
|
| 1636 | * use nr_wake=1.
|
| 1637 |
|
| 1638 | if (nr_wake != 1)
|
| 1639 | return -EINVAL;
|
| 1640 | }
|
| 1641 |
|
| 1642 | retry:
|
| 1643 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
|
| 1644 | if (unlikely(ret != 0))
|
| 1645 | goto out;
|
| 1646 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
|
| 1647 | requeue_pi ? VERIFY_WRITE : VERIFY_READ);
|
| 1648 | if (unlikely(ret != 0))
|
| 1649 | goto out_put_key1;
|
| 1650 |
|
| 1651 | |
| 1652 | * The check above which compares uaddrs is not sufficient for
|
| 1653 | * shared futexes. We need to compare the keys:
|
| 1654 |
|
| 1655 | if (requeue_pi && match_futex(&key1, &key2)) {
|
| 1656 | ret = -EINVAL;
|
| 1657 | goto out_put_keys;
|
| 1658 | }
|
| 1659 |
|
| 1660 | hb1 = hash_futex(&key1);
|
| 1661 | hb2 = hash_futex(&key2);
|
| 1662 |
|
| 1663 | retry_private:
|
| 1664 | hb_waiters_inc(hb2);
|
| 1665 | double_lock_hb(hb1, hb2);
|
| 1666 |
|
| 1667 | if (likely(cmpval != NULL)) {
|
| 1668 | u32 curval;
|
| 1669 |
|
| 1670 | ret = get_futex_value_locked(&curval, uaddr1);
|
| 1671 |
|
| 1672 | if (unlikely(ret)) {
|
| 1673 | double_unlock_hb(hb1, hb2);
|
| 1674 | hb_waiters_dec(hb2);
|
| 1675 |
|
| 1676 | ret = get_user(curval, uaddr1);
|
| 1677 | if (ret)
|
| 1678 | goto out_put_keys;
|
| 1679 |
|
| 1680 | if (!(flags & FLAGS_SHARED))
|
| 1681 | goto retry_private;
|
| 1682 |
|
| 1683 | put_futex_key(&key2);
|
| 1684 | put_futex_key(&key1);
|
| 1685 | goto retry;
|
| 1686 | }
|
| 1687 | if (curval != *cmpval) {
|
| 1688 | ret = -EAGAIN;
|
| 1689 | goto out_unlock;
|
| 1690 | }
|
| 1691 | }
|
| 1692 |
|
| 1693 | if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
|
| 1694 | |
| 1695 | * Attempt to acquire uaddr2 and wake the top waiter. If we
|
| 1696 | * intend to requeue waiters, force setting the FUTEX_WAITERS
|
| 1697 | * bit. We force this here where we are able to easily handle
|
| 1698 | * faults rather in the requeue loop below.
|
| 1699 |
|
| 1700 | ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
|
| 1701 | &key2, &pi_state, nr_requeue);
|
| 1702 |
|
| 1703 | |
| 1704 | * At this point the top_waiter has either taken uaddr2 or is
|
| 1705 | * waiting on it. If the former, then the pi_state will not
|
| 1706 | * exist yet, look it up one more time to ensure we have a
|
| 1707 | * reference to it. If the lock was taken, ret contains the
|
| 1708 | * vpid of the top waiter task.
|
| 1709 |
|
| 1710 | if (ret > 0) {
|
| 1711 | WARN_ON(pi_state);
|
| 1712 | drop_count++;
|
| 1713 | task_count++;
|
| 1714 | |
| 1715 | * If we acquired the lock, then the user
|
| 1716 | * space value of uaddr2 should be vpid. It
|
| 1717 | * cannot be changed by the top waiter as it
|
| 1718 | * is blocked on hb2 lock if it tries to do
|
| 1719 | * so. If something fiddled with it behind our
|
| 1720 | * back the pi state lookup might unearth
|
| 1721 | * it. So we rather use the known value than
|
| 1722 | * rereading and handing potential crap to
|
| 1723 | * lookup_pi_state.
|
| 1724 |
|
| 1725 | ret = lookup_pi_state(ret, hb2, &key2, &pi_state);
|
| 1726 | }
|
| 1727 |
|
| 1728 | switch (ret) {
|
| 1729 | case 0:
|
| 1730 | break;
|
| 1731 | case -EFAULT:
|
| 1732 | free_pi_state(pi_state);
|
| 1733 | pi_state = NULL;
|
| 1734 | double_unlock_hb(hb1, hb2);
|
| 1735 | hb_waiters_dec(hb2);
|
| 1736 | put_futex_key(&key2);
|
| 1737 | put_futex_key(&key1);
|
| 1738 | ret = fault_in_user_writeable(uaddr2);
|
| 1739 | if (!ret)
|
| 1740 | goto retry;
|
| 1741 | goto out;
|
| 1742 | case -EAGAIN:
|
| 1743 | |
| 1744 | * Two reasons for this:
|
| 1745 | * - Owner is exiting and we just wait for the
|
| 1746 | * exit to complete.
|
| 1747 | * - The user space value changed.
|
| 1748 |
|
| 1749 | free_pi_state(pi_state);
|
| 1750 | pi_state = NULL;
|
| 1751 | double_unlock_hb(hb1, hb2);
|
| 1752 | hb_waiters_dec(hb2);
|
| 1753 | put_futex_key(&key2);
|
| 1754 | put_futex_key(&key1);
|
| 1755 | cond_resched();
|
| 1756 | goto retry;
|
| 1757 | default:
|
| 1758 | goto out_unlock;
|
| 1759 | }
|
| 1760 | }
|
| 1761 |
|
| 1762 | plist_for_each_entry_safe(this, next, &hb1->chain, list) {
|
| 1763 | if (task_count - nr_wake >= nr_requeue)
|
| 1764 | break;
|
| 1765 |
|
| 1766 | if (!match_futex(&this->key, &key1))
|
| 1767 | continue;
|
| 1768 |
|
| 1769 | |
| 1770 | * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
|
| 1771 | * be paired with each other and no other futex ops.
|
| 1772 | *
|
| 1773 | * We should never be requeueing a futex_q with a pi_state,
|
| 1774 | * which is awaiting a futex_unlock_pi().
|
| 1775 |
|
| 1776 | if ((requeue_pi && !this->rt_waiter) ||
|
| 1777 | (!requeue_pi && this->rt_waiter) ||
|
| 1778 | this->pi_state) {
|
| 1779 | ret = -EINVAL;
|
| 1780 | break;
|
| 1781 | }
|
| 1782 |
|
| 1783 | |
| 1784 | * Wake nr_wake waiters. For requeue_pi, if we acquired the
|
| 1785 | * lock, we already woke the top_waiter. If not, it will be
|
| 1786 | * woken by futex_unlock_pi().
|
| 1787 |
|
| 1788 | if (++task_count <= nr_wake && !requeue_pi) {
|
| 1789 | mark_wake_futex(&wake_q, this);
|
| 1790 | continue;
|
| 1791 | }
|
| 1792 |
|
| 1793 |
|
| 1794 | if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
|
| 1795 | ret = -EINVAL;
|
| 1796 | break;
|
| 1797 | }
|
| 1798 |
|
| 1799 | |
| 1800 | * Requeue nr_requeue waiters and possibly one more in the case
|
| 1801 | * of requeue_pi if we couldn't acquire the lock atomically.
|
| 1802 |
|
| 1803 | if (requeue_pi) {
|
| 1804 |
|
| 1805 | atomic_inc(&pi_state->refcount);
|
| 1806 | this->pi_state = pi_state;
|
| 1807 | ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
|
| 1808 | this->rt_waiter,
|
| 1809 | this->task);
|
| 1810 | if (ret == 1) {
|
| 1811 |
|
| 1812 | requeue_pi_wake_futex(this, &key2, hb2);
|
| 1813 | drop_count++;
|
| 1814 | continue;
|
| 1815 | } else if (ret) {
|
| 1816 |
|
| 1817 | this->pi_state = NULL;
|
| 1818 | free_pi_state(pi_state);
|
| 1819 | goto out_unlock;
|
| 1820 | }
|
| 1821 | }
|
| 1822 | requeue_futex(this, hb1, hb2, &key2);
|
| 1823 | drop_count++;
|
| 1824 | }
|
| 1825 |
|
| 1826 | out_unlock:
|
| 1827 | free_pi_state(pi_state);
|
| 1828 | double_unlock_hb(hb1, hb2);
|
| 1829 | wake_up_q(&wake_q);
|
| 1830 | hb_waiters_dec(hb2);
|
| 1831 |
|
| 1832 | |
| 1833 | * drop_futex_key_refs() must be called outside the spinlocks. During
|
| 1834 | * the requeue we moved futex_q's from the hash bucket at key1 to the
|
| 1835 | * one at key2 and updated their key pointer. We no longer need to
|
| 1836 | * hold the references to key1.
|
| 1837 |
|
| 1838 | while (--drop_count >= 0)
|
| 1839 | drop_futex_key_refs(&key1);
|
| 1840 |
|
| 1841 | out_put_keys:
|
| 1842 | put_futex_key(&key2);
|
| 1843 | out_put_key1:
|
| 1844 | put_futex_key(&key1);
|
| 1845 | out:
|
| 1846 | return ret ? ret : task_count;
|
| 1847 | }
|
| 1848 |
|
| 1849 |
|
| 1850 | static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
|
| 1851 | __acquires(&hb->lock)
|
| 1852 | {
|
| 1853 | struct futex_hash_bucket *hb;
|
| 1854 |
|
| 1855 | hb = hash_futex(&q->key);
|
| 1856 |
|
| 1857 | |
| 1858 | * Increment the counter before taking the lock so that
|
| 1859 | * a potential waker won't miss a to-be-slept task that is
|
| 1860 | * waiting for the spinlock. This is safe as all queue_lock()
|
| 1861 | * users end up calling queue_me(). Similarly, for housekeeping,
|
| 1862 | * decrement the counter at queue_unlock() when some error has
|
| 1863 | * occurred and we don't end up adding the task to the list.
|
| 1864 |
|
| 1865 | hb_waiters_inc(hb);
|
| 1866 |
|
| 1867 | q->lock_ptr = &hb->lock;
|
| 1868 |
|
| 1869 | spin_lock(&hb->lock);
|
| 1870 | return hb;
|
| 1871 | }
|
| 1872 |
|
| 1873 | static inline void
|
| 1874 | queue_unlock(struct futex_hash_bucket *hb)
|
| 1875 | __releases(&hb->lock)
|
| 1876 | {
|
| 1877 | spin_unlock(&hb->lock);
|
| 1878 | hb_waiters_dec(hb);
|
| 1879 | }
|
| 1880 |
|
| 1881 | |
| 1882 | * queue_me() - Enqueue the futex_q on the futex_hash_bucket
|
| 1883 | * @q: The futex_q to enqueue
|
| 1884 | * @hb: The destination hash bucket
|
| 1885 | *
|
| 1886 | * The hb->lock must be held by the caller, and is released here. A call to
|
| 1887 | * queue_me() is typically paired with exactly one call to unqueue_me(). The
|
| 1888 | * exceptions involve the PI related operations, which may use unqueue_me_pi()
|
| 1889 | * or nothing if the unqueue is done as part of the wake process and the unqueue
|
| 1890 | * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
|
| 1891 | * an example).
|
| 1892 |
|
| 1893 | static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
|
| 1894 | __releases(&hb->lock)
|
| 1895 | {
|
| 1896 | int prio;
|
| 1897 |
|
| 1898 | |
| 1899 | * The priority used to register this element is
|
| 1900 | * - either the real thread-priority for the real-time threads
|
| 1901 | * (i.e. threads with a priority lower than MAX_RT_PRIO)
|
| 1902 | * - or MAX_RT_PRIO for non-RT threads.
|
| 1903 | * Thus, all RT-threads are woken first in priority order, and
|
| 1904 | * the others are woken last, in FIFO order.
|
| 1905 |
|
| 1906 | prio = min(current->normal_prio, MAX_RT_PRIO);
|
| 1907 |
|
| 1908 | plist_node_init(&q->list, prio);
|
| 1909 | plist_add(&q->list, &hb->chain);
|
| 1910 | q->task = current;
|
| 1911 | spin_unlock(&hb->lock);
|
| 1912 | }
|
| 1913 |
|
| 1914 | |
| 1915 | * unqueue_me() - Remove the futex_q from its futex_hash_bucket
|
| 1916 | * @q: The futex_q to unqueue
|
| 1917 | *
|
| 1918 | * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
|
| 1919 | * be paired with exactly one earlier call to queue_me().
|
| 1920 | *
|
| 1921 | * Return:
|
| 1922 | * 1 - if the futex_q was still queued (and we removed unqueued it);
|
| 1923 | * 0 - if the futex_q was already removed by the waking thread
|
| 1924 |
|
| 1925 | static int unqueue_me(struct futex_q *q)
|
| 1926 | {
|
| 1927 | spinlock_t *lock_ptr;
|
| 1928 | int ret = 0;
|
| 1929 |
|
| 1930 |
|
| 1931 | retry:
|
| 1932 | lock_ptr = q->lock_ptr;
|
| 1933 | barrier();
|
| 1934 | if (lock_ptr != NULL) {
|
| 1935 | spin_lock(lock_ptr);
|
| 1936 | |
| 1937 | * q->lock_ptr can change between reading it and
|
| 1938 | * spin_lock(), causing us to take the wrong lock. This
|
| 1939 | * corrects the race condition.
|
| 1940 | *
|
| 1941 | * Reasoning goes like this: if we have the wrong lock,
|
| 1942 | * q->lock_ptr must have changed (maybe several times)
|
| 1943 | * between reading it and the spin_lock(). It can
|
| 1944 | * change again after the spin_lock() but only if it was
|
| 1945 | * already changed before the spin_lock(). It cannot,
|
| 1946 | * however, change back to the original value. Therefore
|
| 1947 | * we can detect whether we acquired the correct lock.
|
| 1948 |
|
| 1949 | if (unlikely(lock_ptr != q->lock_ptr)) {
|
| 1950 | spin_unlock(lock_ptr);
|
| 1951 | goto retry;
|
| 1952 | }
|
| 1953 | __unqueue_futex(q);
|
| 1954 |
|
| 1955 | BUG_ON(q->pi_state);
|
| 1956 |
|
| 1957 | spin_unlock(lock_ptr);
|
| 1958 | ret = 1;
|
| 1959 | }
|
| 1960 |
|
| 1961 | drop_futex_key_refs(&q->key);
|
| 1962 | return ret;
|
| 1963 | }
|
| 1964 |
|
| 1965 | |
| 1966 | * PI futexes can not be requeued and must remove themself from the
|
| 1967 | * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
|
| 1968 | * and dropped here.
|
| 1969 |
|
| 1970 | static void unqueue_me_pi(struct futex_q *q)
|
| 1971 | __releases(q->lock_ptr)
|
| 1972 | {
|
| 1973 | __unqueue_futex(q);
|
| 1974 |
|
| 1975 | BUG_ON(!q->pi_state);
|
| 1976 | free_pi_state(q->pi_state);
|
| 1977 | q->pi_state = NULL;
|
| 1978 |
|
| 1979 | spin_unlock(q->lock_ptr);
|
| 1980 | }
|
| 1981 |
|
| 1982 | |
| 1983 | * Fixup the pi_state owner with the new owner.
|
| 1984 | *
|
| 1985 | * Must be called with hash bucket lock held and mm->sem held for non
|
| 1986 | * private futexes.
|
| 1987 |
|
| 1988 | static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
|
| 1989 | struct task_struct *newowner)
|
| 1990 | {
|
| 1991 | u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
|
| 1992 | struct futex_pi_state *pi_state = q->pi_state;
|
| 1993 | struct task_struct *oldowner = pi_state->owner;
|
| 1994 | u32 uval, uninitialized_var(curval), newval;
|
| 1995 | int ret;
|
| 1996 |
|
| 1997 |
|
| 1998 | if (!pi_state->owner)
|
| 1999 | newtid |= FUTEX_OWNER_DIED;
|
| 2000 |
|
| 2001 | |
| 2002 | * We are here either because we stole the rtmutex from the
|
| 2003 | * previous highest priority waiter or we are the highest priority
|
| 2004 | * waiter but failed to get the rtmutex the first time.
|
| 2005 | * We have to replace the newowner TID in the user space variable.
|
| 2006 | * This must be atomic as we have to preserve the owner died bit here.
|
| 2007 | *
|
| 2008 | * Note: We write the user space value _before_ changing the pi_state
|
| 2009 | * because we can fault here. Imagine swapped out pages or a fork
|
| 2010 | * that marked all the anonymous memory readonly for cow.
|
| 2011 | *
|
| 2012 | * Modifying pi_state _before_ the user space value would
|
| 2013 | * leave the pi_state in an inconsistent state when we fault
|
| 2014 | * here, because we need to drop the hash bucket lock to
|
| 2015 | * handle the fault. This might be observed in the PID check
|
| 2016 | * in lookup_pi_state.
|
| 2017 |
|
| 2018 | retry:
|
| 2019 | if (get_futex_value_locked(&uval, uaddr))
|
| 2020 | goto handle_fault;
|
| 2021 |
|
| 2022 | while (1) {
|
| 2023 | newval = (uval & FUTEX_OWNER_DIED) | newtid;
|
| 2024 |
|
| 2025 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
|
| 2026 | goto handle_fault;
|
| 2027 | if (curval == uval)
|
| 2028 | break;
|
| 2029 | uval = curval;
|
| 2030 | }
|
| 2031 |
|
| 2032 | |
| 2033 | * We fixed up user space. Now we need to fix the pi_state
|
| 2034 | * itself.
|
| 2035 |
|
| 2036 | if (pi_state->owner != NULL) {
|
| 2037 | raw_spin_lock_irq(&pi_state->owner->pi_lock);
|
| 2038 | WARN_ON(list_empty(&pi_state->list));
|
| 2039 | list_del_init(&pi_state->list);
|
| 2040 | raw_spin_unlock_irq(&pi_state->owner->pi_lock);
|
| 2041 | }
|
| 2042 |
|
| 2043 | pi_state->owner = newowner;
|
| 2044 |
|
| 2045 | raw_spin_lock_irq(&newowner->pi_lock);
|
| 2046 | WARN_ON(!list_empty(&pi_state->list));
|
| 2047 | list_add(&pi_state->list, &newowner->pi_state_list);
|
| 2048 | raw_spin_unlock_irq(&newowner->pi_lock);
|
| 2049 | return 0;
|
| 2050 |
|
| 2051 | |
| 2052 | * To handle the page fault we need to drop the hash bucket
|
| 2053 | * lock here. That gives the other task (either the highest priority
|
| 2054 | * waiter itself or the task which stole the rtmutex) the
|
| 2055 | * chance to try the fixup of the pi_state. So once we are
|
| 2056 | * back from handling the fault we need to check the pi_state
|
| 2057 | * after reacquiring the hash bucket lock and before trying to
|
| 2058 | * do another fixup. When the fixup has been done already we
|
| 2059 | * simply return.
|
| 2060 |
|
| 2061 | handle_fault:
|
| 2062 | spin_unlock(q->lock_ptr);
|
| 2063 |
|
| 2064 | ret = fault_in_user_writeable(uaddr);
|
| 2065 |
|
| 2066 | spin_lock(q->lock_ptr);
|
| 2067 |
|
| 2068 | |
| 2069 | * Check if someone else fixed it for us:
|
| 2070 |
|
| 2071 | if (pi_state->owner != oldowner)
|
| 2072 | return 0;
|
| 2073 |
|
| 2074 | if (ret)
|
| 2075 | return ret;
|
| 2076 |
|
| 2077 | goto retry;
|
| 2078 | }
|
| 2079 |
|
| 2080 | static long futex_wait_restart(struct restart_block *restart);
|
| 2081 |
|
| 2082 | |
| 2083 | * fixup_owner() - Post lock pi_state and corner case management
|
| 2084 | * @uaddr: user address of the futex
|
| 2085 | * @q: futex_q (contains pi_state and access to the rt_mutex)
|
| 2086 | * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
|
| 2087 | *
|
| 2088 | * After attempting to lock an rt_mutex, this function is called to cleanup
|
| 2089 | * the pi_state owner as well as handle race conditions that may allow us to
|
| 2090 | * acquire the lock. Must be called with the hb lock held.
|
| 2091 | *
|
| 2092 | * Return:
|
| 2093 | * 1 - success, lock taken;
|
| 2094 | * 0 - success, lock not taken;
|
| 2095 | * <0 - on error (-EFAULT)
|
| 2096 |
|
| 2097 | static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
|
| 2098 | {
|
| 2099 | struct task_struct *owner;
|
| 2100 | int ret = 0;
|
| 2101 |
|
| 2102 | if (locked) {
|
| 2103 | |
| 2104 | * Got the lock. We might not be the anticipated owner if we
|
| 2105 | * did a lock-steal - fix up the PI-state in that case:
|
| 2106 |
|
| 2107 | if (q->pi_state->owner != current)
|
| 2108 | ret = fixup_pi_state_owner(uaddr, q, current);
|
| 2109 | goto out;
|
| 2110 | }
|
| 2111 |
|
| 2112 | |
| 2113 | * Catch the rare case, where the lock was released when we were on the
|
| 2114 | * way back before we locked the hash bucket.
|
| 2115 |
|
| 2116 | if (q->pi_state->owner == current) {
|
| 2117 | |
| 2118 | * Try to get the rt_mutex now. This might fail as some other
|
| 2119 | * task acquired the rt_mutex after we removed ourself from the
|
| 2120 | * rt_mutex waiters list.
|
| 2121 |
|
| 2122 | if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
|
| 2123 | locked = 1;
|
| 2124 | goto out;
|
| 2125 | }
|
| 2126 |
|
| 2127 | |
| 2128 | * pi_state is incorrect, some other task did a lock steal and
|
| 2129 | * we returned due to timeout or signal without taking the
|
| 2130 | * rt_mutex. Too late.
|
| 2131 |
|
| 2132 | raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
|
| 2133 | owner = rt_mutex_owner(&q->pi_state->pi_mutex);
|
| 2134 | if (!owner)
|
| 2135 | owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
|
| 2136 | raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
|
| 2137 | ret = fixup_pi_state_owner(uaddr, q, owner);
|
| 2138 | goto out;
|
| 2139 | }
|
| 2140 |
|
| 2141 | |
| 2142 | * Paranoia check. If we did not take the lock, then we should not be
|
| 2143 | * the owner of the rt_mutex.
|
| 2144 |
|
| 2145 | if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
|
| 2146 | printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
|
| 2147 | "pi-state %p\n", ret,
|
| 2148 | q->pi_state->pi_mutex.owner,
|
| 2149 | q->pi_state->owner);
|
| 2150 |
|
| 2151 | out:
|
| 2152 | return ret ? ret : locked;
|
| 2153 | }
|
| 2154 |
|
| 2155 | |
| 2156 | * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
|
| 2157 | * @hb: the futex hash bucket, must be locked by the caller
|
| 2158 | * @q: the futex_q to queue up on
|
| 2159 | * @timeout: the prepared hrtimer_sleeper, or null for no timeout
|
| 2160 |
|
| 2161 | static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
|
| 2162 | struct hrtimer_sleeper *timeout)
|
| 2163 | {
|
| 2164 | |
| 2165 | * The task state is guaranteed to be set before another task can
|
| 2166 | * wake it. set_current_state() is implemented using smp_store_mb() and
|
| 2167 | * queue_me() calls spin_unlock() upon completion, both serializing
|
| 2168 | * access to the hash list and forcing another memory barrier.
|
| 2169 |
|
| 2170 | set_current_state(TASK_INTERRUPTIBLE);
|
| 2171 | queue_me(q, hb);
|
| 2172 |
|
| 2173 |
|
| 2174 | if (timeout)
|
| 2175 | hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
|
| 2176 |
|
| 2177 | |
| 2178 | * If we have been removed from the hash list, then another task
|
| 2179 | * has tried to wake us, and we can skip the call to schedule().
|
| 2180 |
|
| 2181 | if (likely(!plist_node_empty(&q->list))) {
|
| 2182 | |
| 2183 | * If the timer has already expired, current will already be
|
| 2184 | * flagged for rescheduling. Only call schedule if there
|
| 2185 | * is no timeout, or if it has yet to expire.
|
| 2186 |
|
| 2187 | if (!timeout || timeout->task)
|
| 2188 | freezable_schedule();
|
| 2189 | }
|
| 2190 | __set_current_state(TASK_RUNNING);
|
| 2191 | }
|
| 2192 |
|
| 2193 | |
| 2194 | * futex_wait_setup() - Prepare to wait on a futex
|
| 2195 | * @uaddr: the futex userspace address
|
| 2196 | * @val: the expected value
|
| 2197 | * @flags: futex flags (FLAGS_SHARED, etc.)
|
| 2198 | * @q: the associated futex_q
|
| 2199 | * @hb: storage for hash_bucket pointer to be returned to caller
|
| 2200 | *
|
| 2201 | * Setup the futex_q and locate the hash_bucket. Get the futex value and
|
| 2202 | * compare it with the expected value. Handle atomic faults internally.
|
| 2203 | * Return with the hb lock held and a q.key reference on success, and unlocked
|
| 2204 | * with no q.key reference on failure.
|
| 2205 | *
|
| 2206 | * Return:
|
| 2207 | * 0 - uaddr contains val and hb has been locked;
|
| 2208 | * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
|
| 2209 |
|
| 2210 | static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
|
| 2211 | struct futex_q *q, struct futex_hash_bucket **hb)
|
| 2212 | {
|
| 2213 | u32 uval;
|
| 2214 | int ret;
|
| 2215 |
|
| 2216 | |
| 2217 | * Access the page AFTER the hash-bucket is locked.
|
| 2218 | * Order is important:
|
| 2219 | *
|
| 2220 | * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
|
| 2221 | * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
|
| 2222 | *
|
| 2223 | * The basic logical guarantee of a futex is that it blocks ONLY
|
| 2224 | * if cond(var) is known to be true at the time of blocking, for
|
| 2225 | * any cond. If we locked the hash-bucket after testing *uaddr, that
|
| 2226 | * would open a race condition where we could block indefinitely with
|
| 2227 | * cond(var) false, which would violate the guarantee.
|
| 2228 | *
|
| 2229 | * On the other hand, we insert q and release the hash-bucket only
|
| 2230 | * after testing *uaddr. This guarantees that futex_wait() will NOT
|
| 2231 | * absorb a wakeup if *uaddr does not match the desired values
|
| 2232 | * while the syscall executes.
|
| 2233 |
|
| 2234 | retry:
|
| 2235 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
|
| 2236 | if (unlikely(ret != 0))
|
| 2237 | return ret;
|
| 2238 |
|
| 2239 | retry_private:
|
| 2240 | *hb = queue_lock(q);
|
| 2241 |
|
| 2242 | ret = get_futex_value_locked(&uval, uaddr);
|
| 2243 |
|
| 2244 | if (ret) {
|
| 2245 | queue_unlock(*hb);
|
| 2246 |
|
| 2247 | ret = get_user(uval, uaddr);
|
| 2248 | if (ret)
|
| 2249 | goto out;
|
| 2250 |
|
| 2251 | if (!(flags & FLAGS_SHARED))
|
| 2252 | goto retry_private;
|
| 2253 |
|
| 2254 | put_futex_key(&q->key);
|
| 2255 | goto retry;
|
| 2256 | }
|
| 2257 |
|
| 2258 | if (uval != val) {
|
| 2259 | queue_unlock(*hb);
|
| 2260 | ret = -EWOULDBLOCK;
|
| 2261 | }
|
| 2262 |
|
| 2263 | out:
|
| 2264 | if (ret)
|
| 2265 | put_futex_key(&q->key);
|
| 2266 | return ret;
|
| 2267 | }
|
| 2268 |
|
| 2269 | static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
|
| 2270 | ktime_t *abs_time, u32 bitset)
|
| 2271 | {
|
| 2272 | struct hrtimer_sleeper timeout, *to = NULL;
|
| 2273 | struct restart_block *restart;
|
| 2274 | struct futex_hash_bucket *hb;
|
| 2275 | struct futex_q q = futex_q_init;
|
| 2276 | int ret;
|
| 2277 |
|
| 2278 | if (!bitset)
|
| 2279 | return -EINVAL;
|
| 2280 | q.bitset = bitset;
|
| 2281 |
|
| 2282 | if (abs_time) {
|
| 2283 | to = &timeout;
|
| 2284 |
|
| 2285 | hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
|
| 2286 | CLOCK_REALTIME : CLOCK_MONOTONIC,
|
| 2287 | HRTIMER_MODE_ABS);
|
| 2288 | hrtimer_init_sleeper(to, current);
|
| 2289 | hrtimer_set_expires_range_ns(&to->timer, *abs_time,
|
| 2290 | current->timer_slack_ns);
|
| 2291 | }
|
| 2292 |
|
| 2293 | retry:
|
| 2294 | |
| 2295 | * Prepare to wait on uaddr. On success, holds hb lock and increments
|
| 2296 | * q.key refs.
|
| 2297 |
|
| 2298 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
|
| 2299 | if (ret)
|
| 2300 | goto out;
|
| 2301 |
|
| 2302 |
|
| 2303 | futex_wait_queue_me(hb, &q, to);
|
| 2304 |
|
| 2305 |
|
| 2306 | ret = 0;
|
| 2307 |
|
| 2308 | if (!unqueue_me(&q))
|
| 2309 | goto out;
|
| 2310 | ret = -ETIMEDOUT;
|
| 2311 | if (to && !to->task)
|
| 2312 | goto out;
|
| 2313 |
|
| 2314 | |
| 2315 | * We expect signal_pending(current), but we might be the
|
| 2316 | * victim of a spurious wakeup as well.
|
| 2317 |
|
| 2318 | if (!signal_pending(current))
|
| 2319 | goto retry;
|
| 2320 |
|
| 2321 | ret = -ERESTARTSYS;
|
| 2322 | if (!abs_time)
|
| 2323 | goto out;
|
| 2324 |
|
| 2325 | restart = ¤t->restart_block;
|
| 2326 | restart->fn = futex_wait_restart;
|
| 2327 | restart->futex.uaddr = uaddr;
|
| 2328 | restart->futex.val = val;
|
| 2329 | restart->futex.time = abs_time->tv64;
|
| 2330 | restart->futex.bitset = bitset;
|
| 2331 | restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
|
| 2332 |
|
| 2333 | ret = -ERESTART_RESTARTBLOCK;
|
| 2334 |
|
| 2335 | out:
|
| 2336 | if (to) {
|
| 2337 | hrtimer_cancel(&to->timer);
|
| 2338 | destroy_hrtimer_on_stack(&to->timer);
|
| 2339 | }
|
| 2340 | return ret;
|
| 2341 | }
|
| 2342 |
|
| 2343 |
|
| 2344 | static long futex_wait_restart(struct restart_block *restart)
|
| 2345 | {
|
| 2346 | u32 __user *uaddr = restart->futex.uaddr;
|
| 2347 | ktime_t t, *tp = NULL;
|
| 2348 |
|
| 2349 | if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
|
| 2350 | t.tv64 = restart->futex.time;
|
| 2351 | tp = &t;
|
| 2352 | }
|
| 2353 | restart->fn = do_no_restart_syscall;
|
| 2354 |
|
| 2355 | return (long)futex_wait(uaddr, restart->futex.flags,
|
| 2356 | restart->futex.val, tp, restart->futex.bitset);
|
| 2357 | }
|
| 2358 |
|
| 2359 |
|
| 2360 | |
| 2361 | * Userspace tried a 0 -> TID atomic transition of the futex value
|
| 2362 | * and failed. The kernel side here does the whole locking operation:
|
| 2363 | * if there are waiters then it will block as a consequence of relying
|
| 2364 | * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
|
| 2365 | * a 0 value of the futex too.).
|
| 2366 | *
|
| 2367 | * Also serves as futex trylock_pi()'ing, and due semantics.
|
| 2368 |
|
| 2369 | static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
|
| 2370 | ktime_t *time, int trylock)
|
| 2371 | {
|
| 2372 | struct hrtimer_sleeper timeout, *to = NULL;
|
| 2373 | struct futex_hash_bucket *hb;
|
| 2374 | struct futex_q q = futex_q_init;
|
| 2375 | int res, ret;
|
| 2376 |
|
| 2377 | if (refill_pi_state_cache())
|
| 2378 | return -ENOMEM;
|
| 2379 |
|
| 2380 | if (time) {
|
| 2381 | to = &timeout;
|
| 2382 | hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
|
| 2383 | HRTIMER_MODE_ABS);
|
| 2384 | hrtimer_init_sleeper(to, current);
|
| 2385 | hrtimer_set_expires(&to->timer, *time);
|
| 2386 | }
|
| 2387 |
|
| 2388 | retry:
|
| 2389 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
|
| 2390 | if (unlikely(ret != 0))
|
| 2391 | goto out;
|
| 2392 |
|
| 2393 | retry_private:
|
| 2394 | hb = queue_lock(&q);
|
| 2395 |
|
| 2396 | ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
|
| 2397 | if (unlikely(ret)) {
|
| 2398 | |
| 2399 | * Atomic work succeeded and we got the lock,
|
| 2400 | * or failed. Either way, we do _not_ block.
|
| 2401 |
|
| 2402 | switch (ret) {
|
| 2403 | case 1:
|
| 2404 |
|
| 2405 | ret = 0;
|
| 2406 | goto out_unlock_put_key;
|
| 2407 | case -EFAULT:
|
| 2408 | goto uaddr_faulted;
|
| 2409 | case -EAGAIN:
|
| 2410 | |
| 2411 | * Two reasons for this:
|
| 2412 | * - Task is exiting and we just wait for the
|
| 2413 | * exit to complete.
|
| 2414 | * - The user space value changed.
|
| 2415 |
|
| 2416 | queue_unlock(hb);
|
| 2417 | put_futex_key(&q.key);
|
| 2418 | cond_resched();
|
| 2419 | goto retry;
|
| 2420 | default:
|
| 2421 | goto out_unlock_put_key;
|
| 2422 | }
|
| 2423 | }
|
| 2424 |
|
| 2425 | |
| 2426 | * Only actually queue now that the atomic ops are done:
|
| 2427 |
|
| 2428 | queue_me(&q, hb);
|
| 2429 |
|
| 2430 | WARN_ON(!q.pi_state);
|
| 2431 | |
| 2432 | * Block on the PI mutex:
|
| 2433 |
|
| 2434 | if (!trylock) {
|
| 2435 | ret = rt_mutex_timed_futex_lock(&q.pi_state->pi_mutex, to);
|
| 2436 | } else {
|
| 2437 | ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
|
| 2438 |
|
| 2439 | ret = ret ? 0 : -EWOULDBLOCK;
|
| 2440 | }
|
| 2441 |
|
| 2442 | spin_lock(q.lock_ptr);
|
| 2443 | |
| 2444 | * Fixup the pi_state owner and possibly acquire the lock if we
|
| 2445 | * haven't already.
|
| 2446 |
|
| 2447 | res = fixup_owner(uaddr, &q, !ret);
|
| 2448 | |
| 2449 | * If fixup_owner() returned an error, proprogate that. If it acquired
|
| 2450 | * the lock, clear our -ETIMEDOUT or -EINTR.
|
| 2451 |
|
| 2452 | if (res)
|
| 2453 | ret = (res < 0) ? res : 0;
|
| 2454 |
|
| 2455 | |
| 2456 | * If fixup_owner() faulted and was unable to handle the fault, unlock
|
| 2457 | * it and return the fault to userspace.
|
| 2458 |
|
| 2459 | if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
|
| 2460 | rt_mutex_unlock(&q.pi_state->pi_mutex);
|
| 2461 |
|
| 2462 |
|
| 2463 | unqueue_me_pi(&q);
|
| 2464 |
|
| 2465 | goto out_put_key;
|
| 2466 |
|
| 2467 | out_unlock_put_key:
|
| 2468 | queue_unlock(hb);
|
| 2469 |
|
| 2470 | out_put_key:
|
| 2471 | put_futex_key(&q.key);
|
| 2472 | out:
|
| 2473 | if (to)
|
| 2474 | destroy_hrtimer_on_stack(&to->timer);
|
| 2475 | return ret != -EINTR ? ret : -ERESTARTNOINTR;
|
| 2476 |
|
| 2477 | uaddr_faulted:
|
| 2478 | queue_unlock(hb);
|
| 2479 |
|
| 2480 | ret = fault_in_user_writeable(uaddr);
|
| 2481 | if (ret)
|
| 2482 | goto out_put_key;
|
| 2483 |
|
| 2484 | if (!(flags & FLAGS_SHARED))
|
| 2485 | goto retry_private;
|
| 2486 |
|
| 2487 | put_futex_key(&q.key);
|
| 2488 | goto retry;
|
| 2489 | }
|
| 2490 |
|
| 2491 | |
| 2492 | * Userspace attempted a TID -> 0 atomic transition, and failed.
|
| 2493 | * This is the in-kernel slowpath: we look up the PI state (if any),
|
| 2494 | * and do the rt-mutex unlock.
|
| 2495 |
|
| 2496 | static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
|
| 2497 | {
|
| 2498 | u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
|
| 2499 | union futex_key key = FUTEX_KEY_INIT;
|
| 2500 | struct futex_hash_bucket *hb;
|
| 2501 | struct futex_q *match;
|
| 2502 | int ret;
|
| 2503 |
|
| 2504 | retry:
|
| 2505 | if (get_user(uval, uaddr))
|
| 2506 | return -EFAULT;
|
| 2507 | |
| 2508 | * We release only a lock we actually own:
|
| 2509 |
|
| 2510 | if ((uval & FUTEX_TID_MASK) != vpid)
|
| 2511 | return -EPERM;
|
| 2512 |
|
| 2513 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
|
| 2514 | if (ret)
|
| 2515 | return ret;
|
| 2516 |
|
| 2517 | hb = hash_futex(&key);
|
| 2518 | spin_lock(&hb->lock);
|
| 2519 |
|
| 2520 | |
| 2521 | * Check waiters first. We do not trust user space values at
|
| 2522 | * all and we at least want to know if user space fiddled
|
| 2523 | * with the futex value instead of blindly unlocking.
|
| 2524 |
|
| 2525 | match = futex_top_waiter(hb, &key);
|
| 2526 | if (match) {
|
| 2527 | ret = wake_futex_pi(uaddr, uval, match, hb);
|
| 2528 | |
| 2529 | * In case of success wake_futex_pi dropped the hash
|
| 2530 | * bucket lock.
|
| 2531 |
|
| 2532 | if (!ret)
|
| 2533 | goto out_putkey;
|
| 2534 | |
| 2535 | * The atomic access to the futex value generated a
|
| 2536 | * pagefault, so retry the user-access and the wakeup:
|
| 2537 |
|
| 2538 | if (ret == -EFAULT)
|
| 2539 | goto pi_faulted;
|
| 2540 | |
| 2541 | * wake_futex_pi has detected invalid state. Tell user
|
| 2542 | * space.
|
| 2543 |
|
| 2544 | goto out_unlock;
|
| 2545 | }
|
| 2546 |
|
| 2547 | |
| 2548 | * We have no kernel internal state, i.e. no waiters in the
|
| 2549 | * kernel. Waiters which are about to queue themselves are stuck
|
| 2550 | * on hb->lock. So we can safely ignore them. We do neither
|
| 2551 | * preserve the WAITERS bit not the OWNER_DIED one. We are the
|
| 2552 | * owner.
|
| 2553 |
|
| 2554 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))
|
| 2555 | goto pi_faulted;
|
| 2556 |
|
| 2557 | |
| 2558 | * If uval has changed, let user space handle it.
|
| 2559 |
|
| 2560 | ret = (curval == uval) ? 0 : -EAGAIN;
|
| 2561 |
|
| 2562 | out_unlock:
|
| 2563 | spin_unlock(&hb->lock);
|
| 2564 | out_putkey:
|
| 2565 | put_futex_key(&key);
|
| 2566 | return ret;
|
| 2567 |
|
| 2568 | pi_faulted:
|
| 2569 | spin_unlock(&hb->lock);
|
| 2570 | put_futex_key(&key);
|
| 2571 |
|
| 2572 | ret = fault_in_user_writeable(uaddr);
|
| 2573 | if (!ret)
|
| 2574 | goto retry;
|
| 2575 |
|
| 2576 | return ret;
|
| 2577 | }
|
| 2578 |
|
| 2579 | |
| 2580 | * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
|
| 2581 | * @hb: the hash_bucket futex_q was original enqueued on
|
| 2582 | * @q: the futex_q woken while waiting to be requeued
|
| 2583 | * @key2: the futex_key of the requeue target futex
|
| 2584 | * @timeout: the timeout associated with the wait (NULL if none)
|
| 2585 | *
|
| 2586 | * Detect if the task was woken on the initial futex as opposed to the requeue
|
| 2587 | * target futex. If so, determine if it was a timeout or a signal that caused
|
| 2588 | * the wakeup and return the appropriate error code to the caller. Must be
|
| 2589 | * called with the hb lock held.
|
| 2590 | *
|
| 2591 | * Return:
|
| 2592 | * 0 = no early wakeup detected;
|
| 2593 | * <0 = -ETIMEDOUT or -ERESTARTNOINTR
|
| 2594 |
|
| 2595 | static inline
|
| 2596 | int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
|
| 2597 | struct futex_q *q, union futex_key *key2,
|
| 2598 | struct hrtimer_sleeper *timeout)
|
| 2599 | {
|
| 2600 | int ret = 0;
|
| 2601 |
|
| 2602 | |
| 2603 | * With the hb lock held, we avoid races while we process the wakeup.
|
| 2604 | * We only need to hold hb (and not hb2) to ensure atomicity as the
|
| 2605 | * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
|
| 2606 | * It can't be requeued from uaddr2 to something else since we don't
|
| 2607 | * support a PI aware source futex for requeue.
|
| 2608 |
|
| 2609 | if (!match_futex(&q->key, key2)) {
|
| 2610 | WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
|
| 2611 | |
| 2612 | * We were woken prior to requeue by a timeout or a signal.
|
| 2613 | * Unqueue the futex_q and determine which it was.
|
| 2614 |
|
| 2615 | plist_del(&q->list, &hb->chain);
|
| 2616 | hb_waiters_dec(hb);
|
| 2617 |
|
| 2618 |
|
| 2619 | ret = -EWOULDBLOCK;
|
| 2620 | if (timeout && !timeout->task)
|
| 2621 | ret = -ETIMEDOUT;
|
| 2622 | else if (signal_pending(current))
|
| 2623 | ret = -ERESTARTNOINTR;
|
| 2624 | }
|
| 2625 | return ret;
|
| 2626 | }
|
| 2627 |
|
| 2628 | |
| 2629 | * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
|
| 2630 | * @uaddr: the futex we initially wait on (non-pi)
|
| 2631 | * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
|
| 2632 | * the same type, no requeueing from private to shared, etc.
|
| 2633 | * @val: the expected value of uaddr
|
| 2634 | * @abs_time: absolute timeout
|
| 2635 | * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
|
| 2636 | * @uaddr2: the pi futex we will take prior to returning to user-space
|
| 2637 | *
|
| 2638 | * The caller will wait on uaddr and will be requeued by futex_requeue() to
|
| 2639 | * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
|
| 2640 | * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
|
| 2641 | * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
|
| 2642 | * without one, the pi logic would not know which task to boost/deboost, if
|
| 2643 | * there was a need to.
|
| 2644 | *
|
| 2645 | * We call schedule in futex_wait_queue_me() when we enqueue and return there
|
| 2646 | * via the following--
|
| 2647 | * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
|
| 2648 | * 2) wakeup on uaddr2 after a requeue
|
| 2649 | * 3) signal
|
| 2650 | * 4) timeout
|
| 2651 | *
|
| 2652 | * If 3, cleanup and return -ERESTARTNOINTR.
|
| 2653 | *
|
| 2654 | * If 2, we may then block on trying to take the rt_mutex and return via:
|
| 2655 | * 5) successful lock
|
| 2656 | * 6) signal
|
| 2657 | * 7) timeout
|
| 2658 | * 8) other lock acquisition failure
|
| 2659 | *
|
| 2660 | * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
|
| 2661 | *
|
| 2662 | * If 4 or 7, we cleanup and return with -ETIMEDOUT.
|
| 2663 | *
|
| 2664 | * Return:
|
| 2665 | * 0 - On success;
|
| 2666 | * <0 - On error
|
| 2667 |
|
| 2668 | static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
|
| 2669 | u32 val, ktime_t *abs_time, u32 bitset,
|
| 2670 | u32 __user *uaddr2)
|
| 2671 | {
|
| 2672 | struct hrtimer_sleeper timeout, *to = NULL;
|
| 2673 | struct rt_mutex_waiter rt_waiter;
|
| 2674 | struct rt_mutex *pi_mutex = NULL;
|
| 2675 | struct futex_hash_bucket *hb;
|
| 2676 | union futex_key key2 = FUTEX_KEY_INIT;
|
| 2677 | struct futex_q q = futex_q_init;
|
| 2678 | int res, ret;
|
| 2679 |
|
| 2680 | if (uaddr == uaddr2)
|
| 2681 | return -EINVAL;
|
| 2682 |
|
| 2683 | if (!bitset)
|
| 2684 | return -EINVAL;
|
| 2685 |
|
| 2686 | if (abs_time) {
|
| 2687 | to = &timeout;
|
| 2688 | hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
|
| 2689 | CLOCK_REALTIME : CLOCK_MONOTONIC,
|
| 2690 | HRTIMER_MODE_ABS);
|
| 2691 | hrtimer_init_sleeper(to, current);
|
| 2692 | hrtimer_set_expires_range_ns(&to->timer, *abs_time,
|
| 2693 | current->timer_slack_ns);
|
| 2694 | }
|
| 2695 |
|
| 2696 | |
| 2697 | * The waiter is allocated on our stack, manipulated by the requeue
|
| 2698 | * code while we sleep on uaddr.
|
| 2699 |
|
| 2700 | debug_rt_mutex_init_waiter(&rt_waiter);
|
| 2701 | RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
|
| 2702 | RB_CLEAR_NODE(&rt_waiter.tree_entry);
|
| 2703 | rt_waiter.task = NULL;
|
| 2704 |
|
| 2705 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
|
| 2706 | if (unlikely(ret != 0))
|
| 2707 | goto out;
|
| 2708 |
|
| 2709 | q.bitset = bitset;
|
| 2710 | q.rt_waiter = &rt_waiter;
|
| 2711 | q.requeue_pi_key = &key2;
|
| 2712 |
|
| 2713 | |
| 2714 | * Prepare to wait on uaddr. On success, increments q.key (key1) ref
|
| 2715 | * count.
|
| 2716 |
|
| 2717 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
|
| 2718 | if (ret)
|
| 2719 | goto out_key2;
|
| 2720 |
|
| 2721 | |
| 2722 | * The check above which compares uaddrs is not sufficient for
|
| 2723 | * shared futexes. We need to compare the keys:
|
| 2724 |
|
| 2725 | if (match_futex(&q.key, &key2)) {
|
| 2726 | queue_unlock(hb);
|
| 2727 | ret = -EINVAL;
|
| 2728 | goto out_put_keys;
|
| 2729 | }
|
| 2730 |
|
| 2731 |
|
| 2732 | futex_wait_queue_me(hb, &q, to);
|
| 2733 |
|
| 2734 | spin_lock(&hb->lock);
|
| 2735 | ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
|
| 2736 | spin_unlock(&hb->lock);
|
| 2737 | if (ret)
|
| 2738 | goto out_put_keys;
|
| 2739 |
|
| 2740 | |
| 2741 | * In order for us to be here, we know our q.key == key2, and since
|
| 2742 | * we took the hb->lock above, we also know that futex_requeue() has
|
| 2743 | * completed and we no longer have to concern ourselves with a wakeup
|
| 2744 | * race with the atomic proxy lock acquisition by the requeue code. The
|
| 2745 | * futex_requeue dropped our key1 reference and incremented our key2
|
| 2746 | * reference count.
|
| 2747 |
|
| 2748 |
|
| 2749 |
|
| 2750 | if (!q.rt_waiter) {
|
| 2751 | |
| 2752 | * Got the lock. We might not be the anticipated owner if we
|
| 2753 | * did a lock-steal - fix up the PI-state in that case.
|
| 2754 |
|
| 2755 | if (q.pi_state && (q.pi_state->owner != current)) {
|
| 2756 | spin_lock(q.lock_ptr);
|
| 2757 | ret = fixup_pi_state_owner(uaddr2, &q, current);
|
| 2758 | spin_unlock(q.lock_ptr);
|
| 2759 | }
|
| 2760 | } else {
|
| 2761 | |
| 2762 | * We have been woken up by futex_unlock_pi(), a timeout, or a
|
| 2763 | * signal. futex_unlock_pi() will not destroy the lock_ptr nor
|
| 2764 | * the pi_state.
|
| 2765 |
|
| 2766 | WARN_ON(!q.pi_state);
|
| 2767 | pi_mutex = &q.pi_state->pi_mutex;
|
| 2768 | ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter);
|
| 2769 | debug_rt_mutex_free_waiter(&rt_waiter);
|
| 2770 |
|
| 2771 | spin_lock(q.lock_ptr);
|
| 2772 | |
| 2773 | * Fixup the pi_state owner and possibly acquire the lock if we
|
| 2774 | * haven't already.
|
| 2775 |
|
| 2776 | res = fixup_owner(uaddr2, &q, !ret);
|
| 2777 | |
| 2778 | * If fixup_owner() returned an error, proprogate that. If it
|
| 2779 | * acquired the lock, clear -ETIMEDOUT or -EINTR.
|
| 2780 |
|
| 2781 | if (res)
|
| 2782 | ret = (res < 0) ? res : 0;
|
| 2783 |
|
| 2784 |
|
| 2785 | unqueue_me_pi(&q);
|
| 2786 | }
|
| 2787 |
|
| 2788 | |
| 2789 | * If fixup_pi_state_owner() faulted and was unable to handle the
|
| 2790 | * fault, unlock the rt_mutex and return the fault to userspace.
|
| 2791 |
|
| 2792 | if (ret == -EFAULT) {
|
| 2793 | if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
|
| 2794 | rt_mutex_unlock(pi_mutex);
|
| 2795 | } else if (ret == -EINTR) {
|
| 2796 | |
| 2797 | * We've already been requeued, but cannot restart by calling
|
| 2798 | * futex_lock_pi() directly. We could restart this syscall, but
|
| 2799 | * it would detect that the user space "val" changed and return
|
| 2800 | * -EWOULDBLOCK. Save the overhead of the restart and return
|
| 2801 | * -EWOULDBLOCK directly.
|
| 2802 |
|
| 2803 | ret = -EWOULDBLOCK;
|
| 2804 | }
|
| 2805 |
|
| 2806 | out_put_keys:
|
| 2807 | put_futex_key(&q.key);
|
| 2808 | out_key2:
|
| 2809 | put_futex_key(&key2);
|
| 2810 |
|
| 2811 | out:
|
| 2812 | if (to) {
|
| 2813 | hrtimer_cancel(&to->timer);
|
| 2814 | destroy_hrtimer_on_stack(&to->timer);
|
| 2815 | }
|
| 2816 | return ret;
|
| 2817 | }
|
| 2818 |
|
| 2819 | |
| 2820 | * Support for robust futexes: the kernel cleans up held futexes at
|
| 2821 | * thread exit time.
|
| 2822 | *
|
| 2823 | * Implementation: user-space maintains a per-thread list of locks it
|
| 2824 | * is holding. Upon do_exit(), the kernel carefully walks this list,
|
| 2825 | * and marks all locks that are owned by this thread with the
|
| 2826 | * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
|
| 2827 | * always manipulated with the lock held, so the list is private and
|
| 2828 | * per-thread. Userspace also maintains a per-thread 'list_op_pending'
|
| 2829 | * field, to allow the kernel to clean up if the thread dies after
|
| 2830 | * acquiring the lock, but just before it could have added itself to
|
| 2831 | * the list. There can only be one such pending lock.
|
| 2832 |
|
| 2833 |
|
| 2834 | |
| 2835 | * sys_set_robust_list() - Set the robust-futex list head of a task
|
| 2836 | * @head: pointer to the list-head
|
| 2837 | * @len: length of the list-head, as userspace expects
|
| 2838 |
|
| 2839 | SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
|
| 2840 | size_t, len)
|
| 2841 | {
|
| 2842 | if (!futex_cmpxchg_enabled)
|
| 2843 | return -ENOSYS;
|
| 2844 | |
| 2845 | * The kernel knows only one size for now:
|
| 2846 |
|
| 2847 | if (unlikely(len != sizeof(*head)))
|
| 2848 | return -EINVAL;
|
| 2849 |
|
| 2850 | current->robust_list = head;
|
| 2851 |
|
| 2852 | return 0;
|
| 2853 | }
|
| 2854 |
|
| 2855 | |
| 2856 | * sys_get_robust_list() - Get the robust-futex list head of a task
|
| 2857 | * @pid: pid of the process [zero for current task]
|
| 2858 | * @head_ptr: pointer to a list-head pointer, the kernel fills it in
|
| 2859 | * @len_ptr: pointer to a length field, the kernel fills in the header size
|
| 2860 |
|
| 2861 | SYSCALL_DEFINE3(get_robust_list, int, pid,
|
| 2862 | struct robust_list_head __user * __user *, head_ptr,
|
| 2863 | size_t __user *, len_ptr)
|
| 2864 | {
|
| 2865 | struct robust_list_head __user *head;
|
| 2866 | unsigned long ret;
|
| 2867 | struct task_struct *p;
|
| 2868 |
|
| 2869 | if (!futex_cmpxchg_enabled)
|
| 2870 | return -ENOSYS;
|
| 2871 |
|
| 2872 | rcu_read_lock();
|
| 2873 |
|
| 2874 | ret = -ESRCH;
|
| 2875 | if (!pid)
|
| 2876 | p = current;
|
| 2877 | else {
|
| 2878 | p = find_task_by_vpid(pid);
|
| 2879 | if (!p)
|
| 2880 | goto err_unlock;
|
| 2881 | }
|
| 2882 |
|
| 2883 | ret = -EPERM;
|
| 2884 | if (!ptrace_may_access(p, PTRACE_MODE_READ))
|
| 2885 | goto err_unlock;
|
| 2886 |
|
| 2887 | head = p->robust_list;
|
| 2888 | rcu_read_unlock();
|
| 2889 |
|
| 2890 | if (put_user(sizeof(*head), len_ptr))
|
| 2891 | return -EFAULT;
|
| 2892 | return put_user(head, head_ptr);
|
| 2893 |
|
| 2894 | err_unlock:
|
| 2895 | rcu_read_unlock();
|
| 2896 |
|
| 2897 | return ret;
|
| 2898 | }
|
| 2899 |
|
| 2900 | |
| 2901 | * Process a futex-list entry, check whether it's owned by the
|
| 2902 | * dying task, and do notification if so:
|
| 2903 |
|
| 2904 | int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
|
| 2905 | {
|
| 2906 | u32 uval, uninitialized_var(nval), mval;
|
| 2907 |
|
| 2908 | retry:
|
| 2909 | if (get_user(uval, uaddr))
|
| 2910 | return -1;
|
| 2911 |
|
| 2912 | if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
|
| 2913 | |
| 2914 | * Ok, this dying thread is truly holding a futex
|
| 2915 | * of interest. Set the OWNER_DIED bit atomically
|
| 2916 | * via cmpxchg, and if the value had FUTEX_WAITERS
|
| 2917 | * set, wake up a waiter (if any). (We have to do a
|
| 2918 | * futex_wake() even if OWNER_DIED is already set -
|
| 2919 | * to handle the rare but possible case of recursive
|
| 2920 | * thread-death.) The rest of the cleanup is done in
|
| 2921 | * userspace.
|
| 2922 |
|
| 2923 | mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
|
| 2924 | |
| 2925 | * We are not holding a lock here, but we want to have
|
| 2926 | * the pagefault_disable/enable() protection because
|
| 2927 | * we want to handle the fault gracefully. If the
|
| 2928 | * access fails we try to fault in the futex with R/W
|
| 2929 | * verification via get_user_pages. get_user() above
|
| 2930 | * does not guarantee R/W access. If that fails we
|
| 2931 | * give up and leave the futex locked.
|
| 2932 |
|
| 2933 | if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
|
| 2934 | if (fault_in_user_writeable(uaddr))
|
| 2935 | return -1;
|
| 2936 | goto retry;
|
| 2937 | }
|
| 2938 | if (nval != uval)
|
| 2939 | goto retry;
|
| 2940 |
|
| 2941 | |
| 2942 | * Wake robust non-PI futexes here. The wakeup of
|
| 2943 | * PI futexes happens in exit_pi_state():
|
| 2944 |
|
| 2945 | if (!pi && (uval & FUTEX_WAITERS))
|
| 2946 | futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
|
| 2947 | }
|
| 2948 | return 0;
|
| 2949 | }
|
| 2950 |
|
| 2951 | |
| 2952 | * Fetch a robust-list pointer. Bit 0 signals PI futexes:
|
| 2953 |
|
| 2954 | static inline int fetch_robust_entry(struct robust_list __user **entry,
|
| 2955 | struct robust_list __user * __user *head,
|
| 2956 | unsigned int *pi)
|
| 2957 | {
|
| 2958 | unsigned long uentry;
|
| 2959 |
|
| 2960 | if (get_user(uentry, (unsigned long __user *)head))
|
| 2961 | return -EFAULT;
|
| 2962 |
|
| 2963 | *entry = (void __user *)(uentry & ~1UL);
|
| 2964 | *pi = uentry & 1;
|
| 2965 |
|
| 2966 | return 0;
|
| 2967 | }
|
| 2968 |
|
| 2969 | |
| 2970 | * Walk curr->robust_list (very carefully, it's a userspace list!)
|
| 2971 | * and mark any locks found there dead, and notify any waiters.
|
| 2972 | *
|
| 2973 | * We silently return on any sign of list-walking problem.
|
| 2974 |
|
| 2975 | void exit_robust_list(struct task_struct *curr)
|
| 2976 | {
|
| 2977 | struct robust_list_head __user *head = curr->robust_list;
|
| 2978 | struct robust_list __user *entry, *next_entry, *pending;
|
| 2979 | unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
|
| 2980 | unsigned int uninitialized_var(next_pi);
|
| 2981 | unsigned long futex_offset;
|
| 2982 | int rc;
|
| 2983 |
|
| 2984 | if (!futex_cmpxchg_enabled)
|
| 2985 | return;
|
| 2986 |
|
| 2987 | |
| 2988 | * Fetch the list head (which was registered earlier, via
|
| 2989 | * sys_set_robust_list()):
|
| 2990 |
|
| 2991 | if (fetch_robust_entry(&entry, &head->list.next, &pi))
|
| 2992 | return;
|
| 2993 | |
| 2994 | * Fetch the relative futex offset:
|
| 2995 |
|
| 2996 | if (get_user(futex_offset, &head->futex_offset))
|
| 2997 | return;
|
| 2998 | |
| 2999 | * Fetch any possibly pending lock-add first, and handle it
|
| 3000 | * if it exists:
|
| 3001 |
|
| 3002 | if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
|
| 3003 | return;
|
| 3004 |
|
| 3005 | next_entry = NULL;
|
| 3006 | while (entry != &head->list) {
|
| 3007 | |
| 3008 | * Fetch the next entry in the list before calling
|
| 3009 | * handle_futex_death:
|
| 3010 |
|
| 3011 | rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
|
| 3012 | |
| 3013 | * A pending lock might already be on the list, so
|
| 3014 | * don't process it twice:
|
| 3015 |
|
| 3016 | if (entry != pending)
|
| 3017 | if (handle_futex_death((void __user *)entry + futex_offset,
|
| 3018 | curr, pi))
|
| 3019 | return;
|
| 3020 | if (rc)
|
| 3021 | return;
|
| 3022 | entry = next_entry;
|
| 3023 | pi = next_pi;
|
| 3024 | |
| 3025 | * Avoid excessively long or circular lists:
|
| 3026 |
|
| 3027 | if (!--limit)
|
| 3028 | break;
|
| 3029 |
|
| 3030 | cond_resched();
|
| 3031 | }
|
| 3032 |
|
| 3033 | if (pending)
|
| 3034 | handle_futex_death((void __user *)pending + futex_offset,
|
| 3035 | curr, pip);
|
| 3036 | }
|
| 3037 |
|
| 3038 | long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
|
| 3039 | u32 __user *uaddr2, u32 val2, u32 val3)
|
| 3040 | {
|
| 3041 | int cmd = op & FUTEX_CMD_MASK;
|
| 3042 | unsigned int flags = 0;
|
| 3043 |
|
| 3044 | if (!(op & FUTEX_PRIVATE_FLAG))
|
| 3045 | flags |= FLAGS_SHARED;
|
| 3046 |
|
| 3047 | if (op & FUTEX_CLOCK_REALTIME) {
|
| 3048 | flags |= FLAGS_CLOCKRT;
|
| 3049 | if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
|
| 3050 | return -ENOSYS;
|
| 3051 | }
|
| 3052 |
|
| 3053 | switch (cmd) {
|
| 3054 | case FUTEX_LOCK_PI:
|
| 3055 | case FUTEX_UNLOCK_PI:
|
| 3056 | case FUTEX_TRYLOCK_PI:
|
| 3057 | case FUTEX_WAIT_REQUEUE_PI:
|
| 3058 | case FUTEX_CMP_REQUEUE_PI:
|
| 3059 | if (!futex_cmpxchg_enabled)
|
| 3060 | return -ENOSYS;
|
| 3061 | }
|
| 3062 |
|
| 3063 | switch (cmd) {
|
| 3064 | case FUTEX_WAIT:
|
| 3065 | val3 = FUTEX_BITSET_MATCH_ANY;
|
| 3066 | case FUTEX_WAIT_BITSET:
|
| 3067 | return futex_wait(uaddr, flags, val, timeout, val3);
|
| 3068 | case FUTEX_WAKE:
|
| 3069 | val3 = FUTEX_BITSET_MATCH_ANY;
|
| 3070 | case FUTEX_WAKE_BITSET:
|
| 3071 | return futex_wake(uaddr, flags, val, val3);
|
| 3072 | case FUTEX_REQUEUE:
|
| 3073 | return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
|
| 3074 | case FUTEX_CMP_REQUEUE:
|
| 3075 | return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
|
| 3076 | case FUTEX_WAKE_OP:
|
| 3077 | return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
|
| 3078 | case FUTEX_LOCK_PI:
|
| 3079 | return futex_lock_pi(uaddr, flags, timeout, 0);
|
| 3080 | case FUTEX_UNLOCK_PI:
|
| 3081 | return futex_unlock_pi(uaddr, flags);
|
| 3082 | case FUTEX_TRYLOCK_PI:
|
| 3083 | return futex_lock_pi(uaddr, flags, NULL, 1);
|
| 3084 | case FUTEX_WAIT_REQUEUE_PI:
|
| 3085 | val3 = FUTEX_BITSET_MATCH_ANY;
|
| 3086 | return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
|
| 3087 | uaddr2);
|
| 3088 | case FUTEX_CMP_REQUEUE_PI:
|
| 3089 | return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
|
| 3090 | }
|
| 3091 | return -ENOSYS;
|
| 3092 | }
|
| 3093 |
|
| 3094 |
|
| 3095 | SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
|
| 3096 | struct timespec __user *, utime, u32 __user *, uaddr2,
|
| 3097 | u32, val3)
|
| 3098 | {
|
| 3099 | struct timespec ts;
|
| 3100 | ktime_t t, *tp = NULL;
|
| 3101 | u32 val2 = 0;
|
| 3102 | int cmd = op & FUTEX_CMD_MASK;
|
| 3103 |
|
| 3104 | if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
|
| 3105 | cmd == FUTEX_WAIT_BITSET ||
|
| 3106 | cmd == FUTEX_WAIT_REQUEUE_PI)) {
|
| 3107 | if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
|
| 3108 | return -EFAULT;
|
| 3109 | if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
|
| 3110 | return -EFAULT;
|
| 3111 | if (!timespec_valid(&ts))
|
| 3112 | return -EINVAL;
|
| 3113 |
|
| 3114 | t = timespec_to_ktime(ts);
|
| 3115 | if (cmd == FUTEX_WAIT)
|
| 3116 | t = ktime_add_safe(ktime_get(), t);
|
| 3117 | tp = &t;
|
| 3118 | }
|
| 3119 | |
| 3120 | * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
|
| 3121 | * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
|
| 3122 |
|
| 3123 | if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
|
| 3124 | cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
|
| 3125 | val2 = (u32) (unsigned long) utime;
|
| 3126 |
|
| 3127 | return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
|
| 3128 | }
|
| 3129 |
|
| 3130 | static void __init futex_detect_cmpxchg(void)
|
| 3131 | {
|
| 3132 | #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
|
| 3133 | u32 curval;
|
| 3134 |
|
| 3135 | |
| 3136 | * This will fail and we want it. Some arch implementations do
|
| 3137 | * runtime detection of the futex_atomic_cmpxchg_inatomic()
|
| 3138 | * functionality. We want to know that before we call in any
|
| 3139 | * of the complex code paths. Also we want to prevent
|
| 3140 | * registration of robust lists in that case. NULL is
|
| 3141 | * guaranteed to fault and we get -EFAULT on functional
|
| 3142 | * implementation, the non-functional ones will return
|
| 3143 | * -ENOSYS.
|
| 3144 |
|
| 3145 | if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
|
| 3146 | futex_cmpxchg_enabled = 1;
|
| 3147 | #endif
|
| 3148 | }
|
| 3149 |
|
| 3150 | static int __init futex_init(void)
|
| 3151 | {
|
| 3152 | unsigned int futex_shift;
|
| 3153 | unsigned long i;
|
| 3154 |
|
| 3155 | #if CONFIG_BASE_SMALL
|
| 3156 | futex_hashsize = 16;
|
| 3157 | #else
|
| 3158 | futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
|
| 3159 | #endif
|
| 3160 |
|
| 3161 | futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
|
| 3162 | futex_hashsize, 0,
|
| 3163 | futex_hashsize < 256 ? HASH_SMALL : 0,
|
| 3164 | &futex_shift, NULL,
|
| 3165 | futex_hashsize, futex_hashsize);
|
| 3166 | futex_hashsize = 1UL << futex_shift;
|
| 3167 |
|
| 3168 | futex_detect_cmpxchg();
|
| 3169 |
|
| 3170 | for (i = 0; i < futex_hashsize; i++) {
|
| 3171 | atomic_set(&futex_queues[i].waiters, 0);
|
| 3172 | plist_head_init(&futex_queues[i].chain);
|
| 3173 | spin_lock_init(&futex_queues[i].lock);
|
| 3174 | }
|
| 3175 |
|
| 3176 | return 0;
|
| 3177 | }
|
| 3178 | __initcall(futex_init);
|