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faf8c066df
Without this fix, the rwlock can fail to execute the explicit hand-over in certain cases (e.g., empty critical sections that switch quickly between read and write phases). This can then lead to errors in how __wrphase_futex is accessed, which in turn can lead to deadlocks.
117 lines
3.1 KiB
C
117 lines
3.1 KiB
C
/* Test program for a read-phase / write-phase explicit hand-over.
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Copyright (C) 2017 Free Software Foundation, Inc.
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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 License as
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published by the Free Software Foundation; either version 2.1 of the
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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; see the file COPYING.LIB. If
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not, see <http://www.gnu.org/licenses/>. */
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#include <errno.h>
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#include <error.h>
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#include <pthread.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <stdint.h>
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#include <time.h>
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#include <atomic.h>
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#include <support/xthread.h>
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/* We realy want to set threads to 2 to reproduce this issue. The goal
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is to have one primary writer and a single reader, and to hit the
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bug that happens in the interleaving of those two phase transitions.
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However, on most hardware, adding a second writer seems to help the
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interleaving happen slightly more often, say 20% of the time. On a
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16 core ppc64 machine this fails 100% of the time with an unpatched
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glibc. On a 8 core x86_64 machine this fails ~93% of the time, but
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it doesn't fail at all on a 4 core system, so having available
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unloaded cores makes a big difference in reproducibility. On an 8
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core qemu/kvm guest the reproducer reliability drops to ~10%. */
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#define THREADS 3
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#define KIND PTHREAD_RWLOCK_PREFER_READER_NP
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static pthread_rwlock_t lock;
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static int done = 0;
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static void*
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tf (void* arg)
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{
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while (atomic_load_relaxed (&done) == 0)
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{
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int rcnt = 0;
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int wcnt = 100;
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if ((uintptr_t) arg == 0)
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{
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rcnt = 1;
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wcnt = 1;
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}
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do
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{
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if (wcnt)
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{
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xpthread_rwlock_wrlock (&lock);
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xpthread_rwlock_unlock (&lock);
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wcnt--;
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}
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if (rcnt)
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{
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xpthread_rwlock_rdlock (&lock);
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xpthread_rwlock_unlock (&lock);
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rcnt--;
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}
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}
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while ((atomic_load_relaxed (&done) == 0) && (rcnt + wcnt > 0));
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}
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return NULL;
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}
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static int
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do_test (void)
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{
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pthread_t thr[THREADS];
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int n;
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pthread_rwlockattr_t attr;
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xpthread_rwlockattr_init (&attr);
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xpthread_rwlockattr_setkind_np (&attr, KIND);
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xpthread_rwlock_init (&lock, &attr);
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/* Make standard error the same as standard output. */
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dup2 (1, 2);
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/* Make sure we see all message, even those on stdout. */
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setvbuf (stdout, NULL, _IONBF, 0);
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for (n = 0; n < THREADS; ++n)
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thr[n] = xpthread_create (NULL, tf, (void *) (uintptr_t) n);
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struct timespec delay;
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delay.tv_sec = 10;
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delay.tv_nsec = 0;
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nanosleep (&delay, NULL);
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atomic_store_relaxed (&done, 1);
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/* Wait for all the threads. */
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for (n = 0; n < THREADS; ++n)
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xpthread_join (thr[n]);
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return 0;
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}
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#include <support/test-driver.c>
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