/* Test program for a read-phase / write-phase explicit hand-over. Copyright (C) 2017-2021 Free Software Foundation, Inc. The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. The GNU C Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with the GNU C Library; see the file COPYING.LIB. If not, see <https://www.gnu.org/licenses/>. */ #include <errno.h> #include <error.h> #include <pthread.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <stdint.h> #include <time.h> #include <atomic.h> #include <support/xthread.h> /* We realy want to set threads to 2 to reproduce this issue. The goal is to have one primary writer and a single reader, and to hit the bug that happens in the interleaving of those two phase transitions. However, on most hardware, adding a second writer seems to help the interleaving happen slightly more often, say 20% of the time. On a 16 core ppc64 machine this fails 100% of the time with an unpatched glibc. On a 8 core x86_64 machine this fails ~93% of the time, but it doesn't fail at all on a 4 core system, so having available unloaded cores makes a big difference in reproducibility. On an 8 core qemu/kvm guest the reproducer reliability drops to ~10%. */ #define THREADS 3 #define KIND PTHREAD_RWLOCK_PREFER_READER_NP static pthread_rwlock_t lock; static int done = 0; static void* tf (void* arg) { while (atomic_load_relaxed (&done) == 0) { int rcnt = 0; int wcnt = 100; if ((uintptr_t) arg == 0) { rcnt = 1; wcnt = 1; } do { if (wcnt) { xpthread_rwlock_wrlock (&lock); xpthread_rwlock_unlock (&lock); wcnt--; } if (rcnt) { xpthread_rwlock_rdlock (&lock); xpthread_rwlock_unlock (&lock); rcnt--; } } while ((atomic_load_relaxed (&done) == 0) && (rcnt + wcnt > 0)); } return NULL; } static int do_test (void) { pthread_t thr[THREADS]; int n; pthread_rwlockattr_t attr; xpthread_rwlockattr_init (&attr); xpthread_rwlockattr_setkind_np (&attr, KIND); xpthread_rwlock_init (&lock, &attr); /* Make standard error the same as standard output. */ dup2 (1, 2); /* Make sure we see all message, even those on stdout. */ setvbuf (stdout, NULL, _IONBF, 0); for (n = 0; n < THREADS; ++n) thr[n] = xpthread_create (NULL, tf, (void *) (uintptr_t) n); struct timespec delay; delay.tv_sec = 10; delay.tv_nsec = 0; nanosleep (&delay, NULL); atomic_store_relaxed (&done, 1); /* Wait for all the threads. */ for (n = 0; n < THREADS; ++n) xpthread_join (thr[n]); return 0; } #include <support/test-driver.c>