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POSIX and C++11 require that a thread can destroy a mutex if no other thread owns the mutex, is blocked on the mutex, or will try to acquire it in the future. After destroying the mutex, it can reuse or unmap the underlying memory. Thus, we must not access a mutex' memory after releasing it. Currently, we can load the private flag after releasing the mutex, which is fixed by this patch. See https://sourceware.org/bugzilla/show_bug.cgi?id=13690 for more background. We need to call futex_wake on the lock after releasing it, however. This is by design, and can lead to spurious wake-ups on unrelated futex words (e.g., when the mutex memory is reused for another mutex). This behavior is documented in the glibc-internal futex API and in recent drafts of the Linux kernel's futex documentation (see the draft_futex branch of git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git).
176 lines
5.4 KiB
C
176 lines
5.4 KiB
C
/* Copyright (C) 2003-2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef _LOWLEVELLOCK_H
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#define _LOWLEVELLOCK_H 1
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#include <time.h>
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#include <sys/param.h>
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#include <bits/pthreadtypes.h>
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#include <atomic.h>
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#include <kernel-features.h>
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#include <lowlevellock-futex.h>
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static inline int
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__attribute__ ((always_inline))
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__lll_trylock (int *futex)
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{
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return atomic_compare_and_exchange_val_24_acq (futex, 1, 0) != 0;
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}
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#define lll_trylock(futex) __lll_trylock (&(futex))
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static inline int
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__attribute__ ((always_inline))
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__lll_cond_trylock (int *futex)
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{
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return atomic_compare_and_exchange_val_24_acq (futex, 2, 0) != 0;
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}
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#define lll_cond_trylock(futex) __lll_cond_trylock (&(futex))
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extern void __lll_lock_wait_private (int *futex) attribute_hidden;
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extern void __lll_lock_wait (int *futex, int private) attribute_hidden;
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extern int __lll_robust_lock_wait (int *futex, int private) attribute_hidden;
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static inline void
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__attribute__ ((always_inline))
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__lll_lock (int *futex, int private)
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{
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int val = atomic_compare_and_exchange_val_24_acq (futex, 1, 0);
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if (__glibc_unlikely (val != 0))
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{
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if (__builtin_constant_p (private) && private == LLL_PRIVATE)
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__lll_lock_wait_private (futex);
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else
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__lll_lock_wait (futex, private);
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}
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}
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#define lll_lock(futex, private) __lll_lock (&(futex), private)
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static inline int
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__attribute__ ((always_inline))
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__lll_robust_lock (int *futex, int id, int private)
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{
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int result = 0;
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if (atomic_compare_and_exchange_bool_acq (futex, id, 0) != 0)
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result = __lll_robust_lock_wait (futex, private);
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return result;
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}
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#define lll_robust_lock(futex, id, private) \
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__lll_robust_lock (&(futex), id, private)
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static inline void
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__attribute__ ((always_inline))
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__lll_cond_lock (int *futex, int private)
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{
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int val = atomic_compare_and_exchange_val_24_acq (futex, 2, 0);
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if (__glibc_unlikely (val != 0))
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__lll_lock_wait (futex, private);
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}
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#define lll_cond_lock(futex, private) __lll_cond_lock (&(futex), private)
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#define lll_robust_cond_lock(futex, id, private) \
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__lll_robust_lock (&(futex), (id) | FUTEX_WAITERS, private)
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extern int __lll_timedlock_wait (int *futex, const struct timespec *,
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int private) attribute_hidden;
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extern int __lll_robust_timedlock_wait (int *futex, const struct timespec *,
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int private) attribute_hidden;
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static inline int
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__attribute__ ((always_inline))
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__lll_timedlock (int *futex, const struct timespec *abstime, int private)
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{
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int val = atomic_compare_and_exchange_val_24_acq (futex, 1, 0);
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int result = 0;
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if (__glibc_unlikely (val != 0))
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result = __lll_timedlock_wait (futex, abstime, private);
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return result;
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}
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#define lll_timedlock(futex, abstime, private) \
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__lll_timedlock (&(futex), abstime, private)
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static inline int
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__attribute__ ((always_inline))
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__lll_robust_timedlock (int *futex, const struct timespec *abstime,
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int id, int private)
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{
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int result = 0;
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if (atomic_compare_and_exchange_bool_acq (futex, id, 0) != 0)
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result = __lll_robust_timedlock_wait (futex, abstime, private);
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return result;
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}
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#define lll_robust_timedlock(futex, abstime, id, private) \
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__lll_robust_timedlock (&(futex), abstime, id, private)
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#define lll_unlock(lock, private) \
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((void) ({ \
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int *__futex = &(lock); \
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int __private = (private); \
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int __val = atomic_exchange_24_rel (__futex, 0); \
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if (__glibc_unlikely (__val > 1)) \
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lll_futex_wake (__futex, 1, __private); \
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}))
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#define lll_robust_unlock(lock, private) \
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((void) ({ \
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int *__futex = &(lock); \
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int __private = (private); \
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int __val = atomic_exchange_rel (__futex, 0); \
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if (__glibc_unlikely (__val & FUTEX_WAITERS)) \
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lll_futex_wake (__futex, 1, __private); \
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}))
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#define lll_islocked(futex) \
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(futex != 0)
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/* Initializers for lock. */
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#define LLL_LOCK_INITIALIZER (0)
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#define LLL_LOCK_INITIALIZER_LOCKED (1)
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/* The kernel notifies a process which uses CLONE_CHILD_CLEARTID via futex
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wakeup when the clone terminates. The memory location contains the
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thread ID while the clone is running and is reset to zero
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afterwards. */
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#define lll_wait_tid(tid) \
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do \
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{ \
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__typeof (tid) __tid; \
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while ((__tid = (tid)) != 0) \
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lll_futex_wait (&(tid), __tid, LLL_SHARED); \
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} \
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while (0)
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extern int __lll_timedwait_tid (int *, const struct timespec *)
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attribute_hidden;
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#define lll_timedwait_tid(tid, abstime) \
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({ \
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int __res = 0; \
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if ((tid) != 0) \
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__res = __lll_timedwait_tid (&(tid), (abstime)); \
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__res; \
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})
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#endif /* lowlevellock.h */
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