commit 77e7d626fa6d7f8800c9658e65e43d13c5cdc81d
Author: Torvald Riegel <triegel@redhat.com>
Date:   Mon Jul 24 22:53:38 2017 +0200

    Fix oversight in robust mutex lock acquisition.
    
    65810f0ef05e8c9e333f17a44e77808b163ca298 fixed a robust mutex bug but
    introduced BZ 21778: if the CAS used to try to acquire a lock fails,
    the expected value is not updated, which breaks other cases in the lock
    acquisition loop.  The fix is to simply update the expected value with
    the value returned by the CAS, which ensures that behavior is as if the
    first case with the CAS never happened.
    
    2017-07-25  Torvald Riegel  <triegel@redhat.com>
    
    	[BZ 21778]
    	* nptl/pthread_mutex_timedlock.c (__pthread_mutex_timedlock): Update
    	oldval if the CAS fails.
    	* nptl/pthread_mutex_lock.c (__pthread_mutex_lock_full): Likewise.
    	* nptl/tst-mutex7.c (ROBUST, DELAY_NSEC, ROUNDS, N): New.
    	(tf, do_test): Use them.
    	* nptl/tst-mutex7robust.c: New file.
    	* nptl/Makefile (tests): Add new test.

diff --git a/nptl/Makefile b/nptl/Makefile
index dd01994..bca09bf 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -230,7 +230,7 @@ LDLIBS-tst-thread_local1 = -lstdc++
 
 tests = tst-attr1 tst-attr2 tst-attr3 tst-default-attr \
 	tst-mutex1 tst-mutex2 tst-mutex3 tst-mutex4 tst-mutex5 tst-mutex6 \
-	tst-mutex7 tst-mutex9 tst-mutex5a tst-mutex7a \
+	tst-mutex7 tst-mutex9 tst-mutex5a tst-mutex7a tst-mutex7robust \
 	tst-mutexpi1 tst-mutexpi2 tst-mutexpi3 tst-mutexpi4 tst-mutexpi5 \
 	tst-mutexpi5a tst-mutexpi6 tst-mutexpi7 tst-mutexpi7a \
 	tst-mutexpi9 \
diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index b76475b..8c48503 100644
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -197,11 +197,14 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex)
 	{
 	  /* Try to acquire the lock through a CAS from 0 (not acquired) to
 	     our TID | assume_other_futex_waiters.  */
-	  if (__glibc_likely ((oldval == 0)
-			      && (atomic_compare_and_exchange_bool_acq
-				  (&mutex->__data.__lock,
-				   id | assume_other_futex_waiters, 0) == 0)))
-	      break;
+	  if (__glibc_likely (oldval == 0))
+	    {
+	      oldval
+	        = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
+	            id | assume_other_futex_waiters, 0);
+	      if (__glibc_likely (oldval == 0))
+		break;
+	    }
 
 	  if ((oldval & FUTEX_OWNER_DIED) != 0)
 	    {
diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
index be53381..d5ec314 100644
--- a/nptl/pthread_mutex_timedlock.c
+++ b/nptl/pthread_mutex_timedlock.c
@@ -154,11 +154,14 @@ __pthread_mutex_timedlock (pthread_mutex_t *mutex,
 	{
 	  /* Try to acquire the lock through a CAS from 0 (not acquired) to
 	     our TID | assume_other_futex_waiters.  */
-	  if (__glibc_likely ((oldval == 0)
-			      && (atomic_compare_and_exchange_bool_acq
-				  (&mutex->__data.__lock,
-				   id | assume_other_futex_waiters, 0) == 0)))
-	      break;
+	  if (__glibc_likely (oldval == 0))
+	    {
+	      oldval
+	        = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
+	            id | assume_other_futex_waiters, 0);
+	      if (__glibc_likely (oldval == 0))
+		break;
+	    }
 
 	  if ((oldval & FUTEX_OWNER_DIED) != 0)
 	    {
diff --git a/nptl/tst-mutex7.c b/nptl/tst-mutex7.c
index a11afdb..7990409 100644
--- a/nptl/tst-mutex7.c
+++ b/nptl/tst-mutex7.c
@@ -26,13 +26,22 @@
 #ifndef TYPE
 # define TYPE PTHREAD_MUTEX_DEFAULT
 #endif
-
+#ifndef ROBUST
+# define ROBUST PTHREAD_MUTEX_STALLED
+#endif
+#ifndef DELAY_NSEC
+# define DELAY_NSEC 11000
+#endif
+#ifndef ROUNDS
+# define ROUNDS 1000
+#endif
+#ifndef N
+# define N 100
+#endif
 
 static pthread_mutex_t lock;
 
 
-#define ROUNDS 1000
-#define N 100
 
 
 static void *
@@ -40,7 +49,7 @@ tf (void *arg)
 {
   int nr = (long int) arg;
   int cnt;
-  struct timespec ts = { .tv_sec = 0, .tv_nsec = 11000 };
+  struct timespec ts = { .tv_sec = 0, .tv_nsec = DELAY_NSEC };
 
   for (cnt = 0; cnt < ROUNDS; ++cnt)
     {
@@ -56,7 +65,8 @@ tf (void *arg)
 	  return (void *) 1l;
 	}
 
-      nanosleep (&ts, NULL);
+      if ((ts.tv_sec > 0) || (ts.tv_nsec > 0))
+	nanosleep (&ts, NULL);
     }
 
   return NULL;
@@ -80,6 +90,12 @@ do_test (void)
       exit (1);
     }
 
+  if (pthread_mutexattr_setrobust (&a, ROBUST) != 0)
+    {
+      puts ("mutexattr_setrobust failed");
+      exit (1);
+    }
+
 #ifdef ENABLE_PI
   if (pthread_mutexattr_setprotocol (&a, PTHREAD_PRIO_INHERIT) != 0)
     {
diff --git a/nptl/tst-mutex7robust.c b/nptl/tst-mutex7robust.c
new file mode 100644
index 0000000..73eb66d
--- /dev/null
+++ b/nptl/tst-mutex7robust.c
@@ -0,0 +1,6 @@
+#define TYPE PTHREAD_MUTEX_NORMAL
+#define ROBUST PTHREAD_MUTEX_ROBUST
+#define DELAY_NSEC 0
+#define ROUNDS 1000
+#define N 32
+#include "tst-mutex7.c"
