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389fdf78b2
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).
318 lines
9.3 KiB
C
318 lines
9.3 KiB
C
/* Copyright (C) 2002-2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
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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 <assert.h>
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#include <errno.h>
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#include <stdlib.h>
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#include "pthreadP.h"
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#include <lowlevellock.h>
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#include <stap-probe.h>
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#ifndef lll_unlock_elision
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#define lll_unlock_elision(a,b,c) ({ lll_unlock (a,c); 0; })
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#endif
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static int
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internal_function
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__pthread_mutex_unlock_full (pthread_mutex_t *mutex, int decr)
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__attribute_noinline__;
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int
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internal_function attribute_hidden
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__pthread_mutex_unlock_usercnt (pthread_mutex_t *mutex, int decr)
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{
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int type = PTHREAD_MUTEX_TYPE_ELISION (mutex);
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if (__builtin_expect (type &
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~(PTHREAD_MUTEX_KIND_MASK_NP|PTHREAD_MUTEX_ELISION_FLAGS_NP), 0))
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return __pthread_mutex_unlock_full (mutex, decr);
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if (__builtin_expect (type, PTHREAD_MUTEX_TIMED_NP)
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== PTHREAD_MUTEX_TIMED_NP)
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{
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/* Always reset the owner field. */
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normal:
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mutex->__data.__owner = 0;
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if (decr)
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/* One less user. */
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--mutex->__data.__nusers;
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/* Unlock. */
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lll_unlock (mutex->__data.__lock, PTHREAD_MUTEX_PSHARED (mutex));
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LIBC_PROBE (mutex_release, 1, mutex);
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return 0;
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}
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else if (__glibc_likely (type == PTHREAD_MUTEX_TIMED_ELISION_NP))
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{
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/* Don't reset the owner/users fields for elision. */
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return lll_unlock_elision (mutex->__data.__lock, mutex->__data.__elision,
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PTHREAD_MUTEX_PSHARED (mutex));
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}
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else if (__builtin_expect (PTHREAD_MUTEX_TYPE (mutex)
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== PTHREAD_MUTEX_RECURSIVE_NP, 1))
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{
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/* Recursive mutex. */
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if (mutex->__data.__owner != THREAD_GETMEM (THREAD_SELF, tid))
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return EPERM;
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if (--mutex->__data.__count != 0)
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/* We still hold the mutex. */
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return 0;
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goto normal;
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}
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else if (__builtin_expect (PTHREAD_MUTEX_TYPE (mutex)
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== PTHREAD_MUTEX_ADAPTIVE_NP, 1))
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goto normal;
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else
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{
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/* Error checking mutex. */
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assert (type == PTHREAD_MUTEX_ERRORCHECK_NP);
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if (mutex->__data.__owner != THREAD_GETMEM (THREAD_SELF, tid)
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|| ! lll_islocked (mutex->__data.__lock))
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return EPERM;
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goto normal;
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}
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}
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static int
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internal_function
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__pthread_mutex_unlock_full (pthread_mutex_t *mutex, int decr)
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{
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int newowner = 0;
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switch (PTHREAD_MUTEX_TYPE (mutex))
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{
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case PTHREAD_MUTEX_ROBUST_RECURSIVE_NP:
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/* Recursive mutex. */
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if ((mutex->__data.__lock & FUTEX_TID_MASK)
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== THREAD_GETMEM (THREAD_SELF, tid)
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&& __builtin_expect (mutex->__data.__owner
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== PTHREAD_MUTEX_INCONSISTENT, 0))
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{
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if (--mutex->__data.__count != 0)
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/* We still hold the mutex. */
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return ENOTRECOVERABLE;
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goto notrecoverable;
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}
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if (mutex->__data.__owner != THREAD_GETMEM (THREAD_SELF, tid))
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return EPERM;
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if (--mutex->__data.__count != 0)
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/* We still hold the mutex. */
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return 0;
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goto robust;
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case PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP:
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case PTHREAD_MUTEX_ROBUST_NORMAL_NP:
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case PTHREAD_MUTEX_ROBUST_ADAPTIVE_NP:
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if ((mutex->__data.__lock & FUTEX_TID_MASK)
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!= THREAD_GETMEM (THREAD_SELF, tid)
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|| ! lll_islocked (mutex->__data.__lock))
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return EPERM;
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/* If the previous owner died and the caller did not succeed in
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making the state consistent, mark the mutex as unrecoverable
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and make all waiters. */
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if (__builtin_expect (mutex->__data.__owner
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== PTHREAD_MUTEX_INCONSISTENT, 0))
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notrecoverable:
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newowner = PTHREAD_MUTEX_NOTRECOVERABLE;
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robust:
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/* Remove mutex from the list. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
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&mutex->__data.__list.__next);
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DEQUEUE_MUTEX (mutex);
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mutex->__data.__owner = newowner;
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if (decr)
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/* One less user. */
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--mutex->__data.__nusers;
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/* Unlock. */
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lll_robust_unlock (mutex->__data.__lock,
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PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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break;
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/* The PI support requires the Linux futex system call. If that's not
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available, pthread_mutex_init should never have allowed the type to
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be set. So it will get the default case for an invalid type. */
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#ifdef __NR_futex
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case PTHREAD_MUTEX_PI_RECURSIVE_NP:
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/* Recursive mutex. */
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if (mutex->__data.__owner != THREAD_GETMEM (THREAD_SELF, tid))
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return EPERM;
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if (--mutex->__data.__count != 0)
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/* We still hold the mutex. */
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return 0;
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goto continue_pi_non_robust;
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case PTHREAD_MUTEX_PI_ROBUST_RECURSIVE_NP:
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/* Recursive mutex. */
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if ((mutex->__data.__lock & FUTEX_TID_MASK)
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== THREAD_GETMEM (THREAD_SELF, tid)
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&& __builtin_expect (mutex->__data.__owner
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== PTHREAD_MUTEX_INCONSISTENT, 0))
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{
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if (--mutex->__data.__count != 0)
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/* We still hold the mutex. */
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return ENOTRECOVERABLE;
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goto pi_notrecoverable;
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}
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if (mutex->__data.__owner != THREAD_GETMEM (THREAD_SELF, tid))
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return EPERM;
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if (--mutex->__data.__count != 0)
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/* We still hold the mutex. */
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return 0;
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goto continue_pi_robust;
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case PTHREAD_MUTEX_PI_ERRORCHECK_NP:
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case PTHREAD_MUTEX_PI_NORMAL_NP:
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case PTHREAD_MUTEX_PI_ADAPTIVE_NP:
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case PTHREAD_MUTEX_PI_ROBUST_ERRORCHECK_NP:
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case PTHREAD_MUTEX_PI_ROBUST_NORMAL_NP:
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case PTHREAD_MUTEX_PI_ROBUST_ADAPTIVE_NP:
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if ((mutex->__data.__lock & FUTEX_TID_MASK)
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!= THREAD_GETMEM (THREAD_SELF, tid)
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|| ! lll_islocked (mutex->__data.__lock))
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return EPERM;
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/* If the previous owner died and the caller did not succeed in
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making the state consistent, mark the mutex as unrecoverable
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and make all waiters. */
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if ((mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP) != 0
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&& __builtin_expect (mutex->__data.__owner
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== PTHREAD_MUTEX_INCONSISTENT, 0))
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pi_notrecoverable:
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newowner = PTHREAD_MUTEX_NOTRECOVERABLE;
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if ((mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP) != 0)
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{
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continue_pi_robust:
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/* Remove mutex from the list.
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Note: robust PI futexes are signaled by setting bit 0. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
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(void *) (((uintptr_t) &mutex->__data.__list.__next)
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| 1));
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DEQUEUE_MUTEX (mutex);
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}
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continue_pi_non_robust:
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mutex->__data.__owner = newowner;
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if (decr)
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/* One less user. */
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--mutex->__data.__nusers;
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/* Unlock. Load all necessary mutex data before releasing the mutex
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to not violate the mutex destruction requirements (see
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lll_unlock). */
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int robust = mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP;
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int private = (robust
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? PTHREAD_ROBUST_MUTEX_PSHARED (mutex)
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: PTHREAD_MUTEX_PSHARED (mutex));
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if ((mutex->__data.__lock & FUTEX_WAITERS) != 0
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|| atomic_compare_and_exchange_bool_rel (&mutex->__data.__lock, 0,
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THREAD_GETMEM (THREAD_SELF,
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tid)))
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{
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INTERNAL_SYSCALL_DECL (__err);
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INTERNAL_SYSCALL (futex, __err, 2, &mutex->__data.__lock,
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__lll_private_flag (FUTEX_UNLOCK_PI, private));
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}
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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break;
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#endif /* __NR_futex. */
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case PTHREAD_MUTEX_PP_RECURSIVE_NP:
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/* Recursive mutex. */
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if (mutex->__data.__owner != THREAD_GETMEM (THREAD_SELF, tid))
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return EPERM;
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if (--mutex->__data.__count != 0)
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/* We still hold the mutex. */
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return 0;
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goto pp;
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case PTHREAD_MUTEX_PP_ERRORCHECK_NP:
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/* Error checking mutex. */
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if (mutex->__data.__owner != THREAD_GETMEM (THREAD_SELF, tid)
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|| (mutex->__data.__lock & ~ PTHREAD_MUTEX_PRIO_CEILING_MASK) == 0)
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return EPERM;
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/* FALLTHROUGH */
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case PTHREAD_MUTEX_PP_NORMAL_NP:
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case PTHREAD_MUTEX_PP_ADAPTIVE_NP:
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/* Always reset the owner field. */
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pp:
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mutex->__data.__owner = 0;
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if (decr)
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/* One less user. */
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--mutex->__data.__nusers;
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/* Unlock. */
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int newval, oldval;
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do
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{
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oldval = mutex->__data.__lock;
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newval = oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK;
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}
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while (atomic_compare_and_exchange_bool_rel (&mutex->__data.__lock,
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newval, oldval));
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if ((oldval & ~PTHREAD_MUTEX_PRIO_CEILING_MASK) > 1)
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lll_futex_wake (&mutex->__data.__lock, 1,
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PTHREAD_MUTEX_PSHARED (mutex));
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int oldprio = newval >> PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
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LIBC_PROBE (mutex_release, 1, mutex);
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return __pthread_tpp_change_priority (oldprio, -1);
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default:
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/* Correct code cannot set any other type. */
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return EINVAL;
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}
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LIBC_PROBE (mutex_release, 1, mutex);
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return 0;
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}
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int
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__pthread_mutex_unlock (pthread_mutex_t *mutex)
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{
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return __pthread_mutex_unlock_usercnt (mutex, 1);
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}
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strong_alias (__pthread_mutex_unlock, pthread_mutex_unlock)
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hidden_def (__pthread_mutex_unlock)
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