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739e14f900
Explain that pthread_rwlock_unlock may crash if called on a lock not held by the current thread.
80 lines
2.7 KiB
C
80 lines
2.7 KiB
C
/* Copyright (C) 2003-2016 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Martin Schwidefsky <schwidefsky@de.ibm.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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#include <errno.h>
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#include <sysdep.h>
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#include <lowlevellock.h>
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#include <futex-internal.h>
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#include <pthread.h>
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#include <pthreadP.h>
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#include <stap-probe.h>
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#include <elide.h>
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/* Unlock RWLOCK. */
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int
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__pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
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{
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int futex_shared =
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rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
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LIBC_PROBE (rwlock_unlock, 1, rwlock);
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/* Trying to elide an unlocked lock may crash the process. This
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is expected and is compatible with POSIX.1-2008: "results are
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undefined if the read-write lock rwlock is not held by the
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calling thread". */
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if (ELIDE_UNLOCK (rwlock->__data.__writer == 0
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&& rwlock->__data.__nr_readers == 0))
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return 0;
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lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
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if (rwlock->__data.__writer)
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rwlock->__data.__writer = 0;
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else
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--rwlock->__data.__nr_readers;
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/* If there are still readers present, we do not yet need to wake writers
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nor are responsible to wake any readers. */
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if (rwlock->__data.__nr_readers == 0)
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{
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/* Note that if there is a blocked writer, we effectively make it
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responsible for waking any readers because we don't wake readers in
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this case. */
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if (rwlock->__data.__nr_writers_queued)
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{
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++rwlock->__data.__writer_wakeup;
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lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
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futex_wake (&rwlock->__data.__writer_wakeup, 1, futex_shared);
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return 0;
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}
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else if (rwlock->__data.__nr_readers_queued)
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{
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++rwlock->__data.__readers_wakeup;
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lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
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futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX,
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futex_shared);
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return 0;
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}
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}
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lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
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return 0;
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}
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weak_alias (__pthread_rwlock_unlock, pthread_rwlock_unlock)
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hidden_def (__pthread_rwlock_unlock)
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