Althought, it is undefined behavior, there is no reason for segfault. Program received signal SIGSEGV, Segmentation fault. __pthread_unlock (lock=lock@entry=0x804b03c <lock+16>) at libpthread/linuxthreads.old/spinlock.c:231 231 (&lock->__status, oldstatus, (long)(thr->p_nextlock) & ~1L)) It occurs only on platforms which has HAS_COMPARE_AND_SWAP defined. Restore glibc commit fbaf6e72d6 "spinlock.c (__pthread_unlock): Don't crash if called for an untaken mutex." behavior, broken later by commit 4ad1d0cfbf. Signed-off-by: Leonid Lisovskiy &lt;lly.dev(a)gmail.com&gt; --- libpthread/linuxthreads/spinlock.c | 12 ++++++-- test/pthread/ex8-mtx-odd.c | 56 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 65 insertions(+), 3 deletions(-) create mode 100644 test/pthread/ex8-mtx-odd.c diff --git a/libpthread/linuxthreads/spinlock.c b/libpthread/linuxthreads/spinlock.c index 80aeda5..ce97002 100644 --- a/libpthread/linuxthreads/spinlock.c +++ b/libpthread/linuxthreads/spinlock.c @@ -188,10 +188,16 @@ int __pthread_unlock(struct _pthread_fastlock * lock) WRITE_MEMORY_BARRIER(); again: - while ((oldstatus = lock->__status) == 1) { - if (__compare_and_swap_with_release_semantics(&lock->__status, + oldstatus = lock->__status; + if (oldstatus == 0 || oldstatus == 1) { + /* No threads are waiting for this lock. Please note that we also + enter this case if the lock is not taken at all. If this wouldn't + be done here we would crash further down. */ + if (! __compare_and_swap_with_release_semantics(&lock->__status, oldstatus, 0)) - return 0; + goto again; + + return 0; } /* Find thread in waiting queue with maximal priority */ diff --git a/test/pthread/ex8-mtx-odd.c b/test/pthread/ex8-mtx-odd.c new file mode 100644 index 0000000..791b2c2 --- /dev/null +++ b/test/pthread/ex8-mtx-odd.c @@ -0,0 +1,56 @@ +/* Copyright (C) 2002 Free Software Foundation, Inc. + This file is part of the GNU C Library. + Contributed by Ulrich Drepper &lt;drepper(a)redhat.com&gt;om>, 2002. + + 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; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA + 02111-1307 USA. */ + +#include <errno.h> +#include <pthread.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <time.h> + + +static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER; + +static int +do_test (void) +{ + + if (pthread_mutex_lock (&lock) != 0) + { + puts ("mutex_lock failed"); + exit (1); + } + + if (pthread_mutex_unlock (&lock) != 0) + { + puts ("1st mutex_unlock failed"); + exit (1); + } + + if (pthread_mutex_unlock (&lock) != 0) + { + puts ("2nd mutex_unlock failed"); + exit (1); + } + + return 0; +} + +#define TEST_FUNCTION do_test () +#include "../test-skeleton.c" -- 1.8.5.6