29 May
2016
29 May
'16
7:06 a.m.
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 <lly.dev(a)gmail.com>
---
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 <drepper(a)redhat.com>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