Don't do lock elision on an error checking mutex (bug 17514)

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.

3 files changed, 64 insertions, 2 deletions

diff --git a/nptl/Makefile b/nptl/Makefile
index 6d3d711..dc3ccab 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -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
diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
index 9055e11..07f0901 100644
--- a/nptl/pthread_mutex_timedlock.c
+++ b/nptl/pthread_mutex_timedlock.c
@@ -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);
diff --git a/nptl/tst-mutex-errorcheck.c b/nptl/tst-mutex-errorcheck.c
new file mode 100644
index 0000000..7b75611
--- /dev/null
+++ b/nptl/tst-mutex-errorcheck.c
@@ -0,0 +1,61 @@
+/* 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>
+
+static int
+do_test (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;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"