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a9f60b1571
While debugging a kernel warning, Thomas Gleixner, Sebastian Sewior and Heiko Carstens found a bug in pthread_mutex_trylock due to misordered instructions: 140: a5 1b 00 01 oill %r1,1 144: e5 48 a0 f0 00 00 mvghi 240(%r10),0 <--- THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL); 14a: e3 10 a0 e0 00 24 stg %r1,224(%r10) <--- last THREAD_SETMEM of ENQUEUE_MUTEX_PI vs (with compiler barriers): 140: a5 1b 00 01 oill %r1,1 144: e3 10 a0 e0 00 24 stg %r1,224(%r10) 14a: e5 48 a0 f0 00 00 mvghi 240(%r10),0 Please have a look at the discussion: "Re: WARN_ON_ONCE(!new_owner) within wake_futex_pi() triggerede" (https://lore.kernel.org/lkml/20190202112006.GB3381@osiris/) This patch is introducing the same compiler barriers and comments for pthread_mutex_trylock as introduced for pthread_mutex_lock and pthread_mutex_timedlock by commit8f9450a0b7"Add compiler barriers around modifications of the robust mutex list." ChangeLog: [BZ #24180] * nptl/pthread_mutex_trylock.c (__pthread_mutex_trylock): Add compiler barriers and comments. (cherry picked from commit823624bdc4)
470 lines
14 KiB
C
470 lines
14 KiB
C
/* Copyright (C) 2002-2018 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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#ifndef lll_trylock_elision
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#define lll_trylock_elision(a,t) lll_trylock(a)
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#endif
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#ifndef FORCE_ELISION
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#define FORCE_ELISION(m, s)
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#endif
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int
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__pthread_mutex_trylock (pthread_mutex_t *mutex)
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{
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int oldval;
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pid_t id = THREAD_GETMEM (THREAD_SELF, tid);
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/* See concurrency notes regarding mutex type which is loaded from __kind
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in struct __pthread_mutex_s in sysdeps/nptl/bits/thread-shared-types.h. */
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switch (__builtin_expect (PTHREAD_MUTEX_TYPE_ELISION (mutex),
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PTHREAD_MUTEX_TIMED_NP))
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{
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/* Recursive mutex. */
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case PTHREAD_MUTEX_RECURSIVE_NP|PTHREAD_MUTEX_ELISION_NP:
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case PTHREAD_MUTEX_RECURSIVE_NP:
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/* Check whether we already hold the mutex. */
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if (mutex->__data.__owner == id)
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{
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/* Just bump the counter. */
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if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
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/* Overflow of the counter. */
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return EAGAIN;
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++mutex->__data.__count;
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return 0;
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}
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if (lll_trylock (mutex->__data.__lock) == 0)
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{
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/* Record the ownership. */
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mutex->__data.__owner = id;
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mutex->__data.__count = 1;
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++mutex->__data.__nusers;
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return 0;
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}
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break;
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case PTHREAD_MUTEX_TIMED_ELISION_NP:
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elision: __attribute__((unused))
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if (lll_trylock_elision (mutex->__data.__lock,
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mutex->__data.__elision) != 0)
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break;
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/* Don't record the ownership. */
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return 0;
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case PTHREAD_MUTEX_TIMED_NP:
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FORCE_ELISION (mutex, goto elision);
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/*FALL THROUGH*/
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case PTHREAD_MUTEX_ADAPTIVE_NP:
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case PTHREAD_MUTEX_ERRORCHECK_NP:
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if (lll_trylock (mutex->__data.__lock) != 0)
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break;
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/* Record the ownership. */
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mutex->__data.__owner = id;
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++mutex->__data.__nusers;
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return 0;
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case PTHREAD_MUTEX_ROBUST_RECURSIVE_NP:
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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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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
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&mutex->__data.__list.__next);
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/* We need to set op_pending before starting the operation. Also
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see comments at ENQUEUE_MUTEX. */
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__asm ("" ::: "memory");
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oldval = mutex->__data.__lock;
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do
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{
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again:
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if ((oldval & FUTEX_OWNER_DIED) != 0)
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{
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/* The previous owner died. Try locking the mutex. */
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int newval = id | (oldval & FUTEX_WAITERS);
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newval
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= atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
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newval, oldval);
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if (newval != oldval)
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{
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oldval = newval;
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goto again;
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}
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/* We got the mutex. */
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mutex->__data.__count = 1;
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/* But it is inconsistent unless marked otherwise. */
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mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
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/* We must not enqueue the mutex before we have acquired it.
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Also see comments at ENQUEUE_MUTEX. */
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__asm ("" ::: "memory");
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ENQUEUE_MUTEX (mutex);
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/* We need to clear op_pending after we enqueue the mutex. */
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__asm ("" ::: "memory");
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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/* Note that we deliberately exist here. If we fall
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through to the end of the function __nusers would be
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incremented which is not correct because the old
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owner has to be discounted. */
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return EOWNERDEAD;
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}
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/* Check whether we already hold the mutex. */
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if (__glibc_unlikely ((oldval & FUTEX_TID_MASK) == id))
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{
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int kind = PTHREAD_MUTEX_TYPE (mutex);
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if (kind == PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP)
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{
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/* We do not need to ensure ordering wrt another memory
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access. Also see comments at ENQUEUE_MUTEX. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
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NULL);
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return EDEADLK;
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}
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if (kind == PTHREAD_MUTEX_ROBUST_RECURSIVE_NP)
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{
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/* We do not need to ensure ordering wrt another memory
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access. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
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NULL);
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/* Just bump the counter. */
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if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
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/* Overflow of the counter. */
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return EAGAIN;
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++mutex->__data.__count;
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return 0;
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}
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}
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oldval = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
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id, 0);
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if (oldval != 0 && (oldval & FUTEX_OWNER_DIED) == 0)
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{
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/* We haven't acquired the lock as it is already acquired by
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another owner. We do not need to ensure ordering wrt another
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memory access. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return EBUSY;
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}
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if (__builtin_expect (mutex->__data.__owner
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== PTHREAD_MUTEX_NOTRECOVERABLE, 0))
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{
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/* This mutex is now not recoverable. */
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mutex->__data.__count = 0;
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if (oldval == id)
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lll_unlock (mutex->__data.__lock,
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PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
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/* FIXME This violates the mutex destruction requirements. See
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__pthread_mutex_unlock_full. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return ENOTRECOVERABLE;
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}
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}
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while ((oldval & FUTEX_OWNER_DIED) != 0);
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/* We must not enqueue the mutex before we have acquired it.
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Also see comments at ENQUEUE_MUTEX. */
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__asm ("" ::: "memory");
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ENQUEUE_MUTEX (mutex);
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/* We need to clear op_pending after we enqueue the mutex. */
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__asm ("" ::: "memory");
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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mutex->__data.__owner = id;
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++mutex->__data.__nusers;
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mutex->__data.__count = 1;
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return 0;
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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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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_RECURSIVE_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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{
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int kind, robust;
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{
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/* See concurrency notes regarding __kind in struct __pthread_mutex_s
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in sysdeps/nptl/bits/thread-shared-types.h. */
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int mutex_kind = atomic_load_relaxed (&(mutex->__data.__kind));
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kind = mutex_kind & PTHREAD_MUTEX_KIND_MASK_NP;
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robust = mutex_kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP;
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}
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if (robust)
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{
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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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/* We need to set op_pending before starting the operation. Also
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see comments at ENQUEUE_MUTEX. */
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__asm ("" ::: "memory");
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}
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oldval = mutex->__data.__lock;
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/* Check whether we already hold the mutex. */
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if (__glibc_unlikely ((oldval & FUTEX_TID_MASK) == id))
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{
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if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
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{
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/* We do not need to ensure ordering wrt another memory
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access. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return EDEADLK;
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}
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if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
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{
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/* We do not need to ensure ordering wrt another memory
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access. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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/* Just bump the counter. */
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if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
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/* Overflow of the counter. */
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return EAGAIN;
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++mutex->__data.__count;
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return 0;
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}
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}
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oldval
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= atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
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id, 0);
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if (oldval != 0)
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{
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if ((oldval & FUTEX_OWNER_DIED) == 0)
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{
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/* We haven't acquired the lock as it is already acquired by
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another owner. We do not need to ensure ordering wrt another
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memory access. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return EBUSY;
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}
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assert (robust);
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/* The mutex owner died. The kernel will now take care of
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everything. */
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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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INTERNAL_SYSCALL_DECL (__err);
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int e = INTERNAL_SYSCALL (futex, __err, 4, &mutex->__data.__lock,
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__lll_private_flag (FUTEX_TRYLOCK_PI,
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private), 0, 0);
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if (INTERNAL_SYSCALL_ERROR_P (e, __err)
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&& INTERNAL_SYSCALL_ERRNO (e, __err) == EWOULDBLOCK)
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{
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/* The kernel has not yet finished the mutex owner death.
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We do not need to ensure ordering wrt another memory
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access. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return EBUSY;
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}
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oldval = mutex->__data.__lock;
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}
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if (__glibc_unlikely (oldval & FUTEX_OWNER_DIED))
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{
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atomic_and (&mutex->__data.__lock, ~FUTEX_OWNER_DIED);
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/* We got the mutex. */
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mutex->__data.__count = 1;
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/* But it is inconsistent unless marked otherwise. */
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mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
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/* We must not enqueue the mutex before we have acquired it.
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Also see comments at ENQUEUE_MUTEX. */
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__asm ("" ::: "memory");
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ENQUEUE_MUTEX (mutex);
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/* We need to clear op_pending after we enqueue the mutex. */
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__asm ("" ::: "memory");
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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/* Note that we deliberately exit here. If we fall
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through to the end of the function __nusers would be
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incremented which is not correct because the old owner
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has to be discounted. */
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return EOWNERDEAD;
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}
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if (robust
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&& __builtin_expect (mutex->__data.__owner
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== PTHREAD_MUTEX_NOTRECOVERABLE, 0))
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{
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/* This mutex is now not recoverable. */
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mutex->__data.__count = 0;
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INTERNAL_SYSCALL_DECL (__err);
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INTERNAL_SYSCALL (futex, __err, 4, &mutex->__data.__lock,
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__lll_private_flag (FUTEX_UNLOCK_PI,
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PTHREAD_ROBUST_MUTEX_PSHARED (mutex)),
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0, 0);
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/* To the kernel, this will be visible after the kernel has
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acquired the mutex in the syscall. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return ENOTRECOVERABLE;
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}
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if (robust)
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{
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/* We must not enqueue the mutex before we have acquired it.
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Also see comments at ENQUEUE_MUTEX. */
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__asm ("" ::: "memory");
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ENQUEUE_MUTEX_PI (mutex);
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/* We need to clear op_pending after we enqueue the mutex. */
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__asm ("" ::: "memory");
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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}
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mutex->__data.__owner = id;
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++mutex->__data.__nusers;
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mutex->__data.__count = 1;
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return 0;
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}
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#endif /* __NR_futex. */
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case PTHREAD_MUTEX_PP_RECURSIVE_NP:
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case PTHREAD_MUTEX_PP_ERRORCHECK_NP:
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case PTHREAD_MUTEX_PP_NORMAL_NP:
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case PTHREAD_MUTEX_PP_ADAPTIVE_NP:
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{
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/* See concurrency notes regarding __kind in struct __pthread_mutex_s
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in sysdeps/nptl/bits/thread-shared-types.h. */
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int kind = atomic_load_relaxed (&(mutex->__data.__kind))
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& PTHREAD_MUTEX_KIND_MASK_NP;
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oldval = mutex->__data.__lock;
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/* Check whether we already hold the mutex. */
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if (mutex->__data.__owner == id)
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{
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if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
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return EDEADLK;
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if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
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{
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/* Just bump the counter. */
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if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
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/* Overflow of the counter. */
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return EAGAIN;
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++mutex->__data.__count;
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return 0;
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}
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}
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int oldprio = -1, ceilval;
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do
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{
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int ceiling = (oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK)
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>> PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
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if (__pthread_current_priority () > ceiling)
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{
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if (oldprio != -1)
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__pthread_tpp_change_priority (oldprio, -1);
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return EINVAL;
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}
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int retval = __pthread_tpp_change_priority (oldprio, ceiling);
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if (retval)
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return retval;
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ceilval = ceiling << PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
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oldprio = ceiling;
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oldval
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= atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
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ceilval | 1, ceilval);
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if (oldval == ceilval)
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break;
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}
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while ((oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK) != ceilval);
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if (oldval != ceilval)
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{
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__pthread_tpp_change_priority (oldprio, -1);
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break;
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}
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assert (mutex->__data.__owner == 0);
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/* Record the ownership. */
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mutex->__data.__owner = id;
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++mutex->__data.__nusers;
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mutex->__data.__count = 1;
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return 0;
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}
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break;
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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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return EBUSY;
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}
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#ifndef __pthread_mutex_trylock
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#ifndef pthread_mutex_trylock
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weak_alias (__pthread_mutex_trylock, pthread_mutex_trylock)
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hidden_def (__pthread_mutex_trylock)
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#endif
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#endif
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