Don't do lock elision on an error checking mutex (bug 17514)
Commit Message
Error checking mutexes are not supposed to be subject to lock elision.
That would defeat the error checking nature of the mutex because lock
elision doesn't record ownership.
[BZ #17514]
* nptl/pthread_mutex_timedlock.c (pthread_mutex_timedlock)
<case PTHREAD_MUTEX_ERRORCHECK_NP>: Don't do lock elision.
* nptl/Makefile (tests): Add tst-mutex-errorcheck.
* nptl/tst-mutex-errorcheck.c: New file.
---
nptl/Makefile | 2 +-
nptl/pthread_mutex_timedlock.c | 3 ++-
nptl/tst-mutex-errorcheck.c | 58 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 61 insertions(+), 2 deletions(-)
create mode 100644 nptl/tst-mutex-errorcheck.c
Comments
On 2016-01-14 12:49, Andreas Schwab wrote:
> Error checking mutexes are not supposed to be subject to lock elision.
> That would defeat the error checking nature of the mutex because lock
> elision doesn't record ownership.
>
> [BZ #17514]
> * nptl/pthread_mutex_timedlock.c (pthread_mutex_timedlock)
> <case PTHREAD_MUTEX_ERRORCHECK_NP>: Don't do lock elision.
> * nptl/Makefile (tests): Add tst-mutex-errorcheck.
> * nptl/tst-mutex-errorcheck.c: New file.
> ---
> nptl/Makefile | 2 +-
> nptl/pthread_mutex_timedlock.c | 3 ++-
> nptl/tst-mutex-errorcheck.c | 58 ++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 61 insertions(+), 2 deletions(-)
> create mode 100644 nptl/tst-mutex-errorcheck.c
Thanks for the patch. I confirm it fixes the error reported in bugs
nptl/17514 and nptl/19515.
@@ -288,7 +288,7 @@ tests = tst-typesizes \
tst-initializers1 $(addprefix tst-initializers1-,\
c89 gnu89 c99 gnu99 c11 gnu11) \
tst-bad-schedattr \
- tst-thread_local1
+ tst-thread_local1 tst-mutex-errorcheck
xtests = tst-setuid1 tst-setuid1-static tst-setuid2 \
tst-mutexpp1 tst-mutexpp6 tst-mutexpp10
test-srcs = tst-oddstacklimit
@@ -89,7 +89,8 @@ pthread_mutex_timedlock (pthread_mutex_t *mutex,
if (__glibc_unlikely (mutex->__data.__owner == id))
return EDEADLK;
- /* FALLTHROUGH */
+ /* Don't do lock elision on an error checking mutex. */
+ goto simple;
case PTHREAD_MUTEX_TIMED_NP:
FORCE_ELISION (mutex, goto elision);
new file mode 100644
@@ -0,0 +1,58 @@
+/* Check that error checking mutexes are not subject to lock elision.
+ Copyright (C) 2016 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ 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, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <stdio.h>
+#include <errno.h>
+#include <time.h>
+#include <pthread.h>
+
+int
+main (void)
+{
+ struct timespec tms = { 0 };
+ pthread_mutex_t mutex;
+ pthread_mutexattr_t mutexattr;
+ int ret = 0;
+
+ if (pthread_mutexattr_init (&mutexattr) != 0)
+ return 1;
+ if (pthread_mutexattr_settype (&mutexattr, PTHREAD_MUTEX_ERRORCHECK) != 0)
+ return 1;
+
+ if (pthread_mutex_init (&mutex, &mutexattr) != 0)
+ return 1;
+ if (pthread_mutexattr_destroy (&mutexattr) != 0)
+ return 1;
+
+ /* The call to pthread_mutex_timedlock erroneously enabled lock elision
+ on the mutex, which then triggered an assertion failure in
+ pthread_mutex_unlock. It would also defeat the error checking nature
+ of the mutex. */
+ if (pthread_mutex_timedlock (&mutex, &tms) != 0)
+ return 1;
+ if (pthread_mutex_timedlock (&mutex, &tms) != EDEADLK)
+ {
+ printf ("Failed error checking on locked mutex\n");
+ ret = 1;
+ }
+
+ if (pthread_mutex_unlock (&mutex) != 0)
+ ret = 1;
+
+ return ret;
+}