Fix rwlock stall with PREFER_WRITER_NONRECURSIVE_NP (bug 23861)

In the read lock function (__pthread_rwlock_rdlock_full) there was a
code path which would fail to reload __readers while waiting for
PTHREAD_RWLOCK_RWAITING to change. This failure to reload __readers
into a local value meant that various conditionals used the old value
of __readers and with only two threads left it could result in an
indefinite stall of one of the readers (waiting for PTHREAD_RWLOCK_RWAITING
to go to zero, but it never would).

1 files changed, 1 insertions, 1 deletions

diff --git a/nptl/pthread_rwlock_common.c b/nptl/pthread_rwlock_common.c
index 5dd534271a..85fc1bcfc7 100644
--- a/nptl/pthread_rwlock_common.c
+++ b/nptl/pthread_rwlock_common.c
@@ -314,7 +314,7 @@ __pthread_rwlock_rdlock_full (pthread_rwlock_t *rwlock,
 		 harmless because the flag is just about the state of
 		 __readers, and all threads set the flag under the same
 		 conditions.  */
-	      while ((atomic_load_relaxed (&rwlock->__data.__readers)
+	      while (((r = atomic_load_relaxed (&rwlock->__data.__readers))
 		      & PTHREAD_RWLOCK_RWAITING) != 0)
 		{
 		  int private = __pthread_rwlock_get_private (rwlock);