Fix missing wake-ups in pthread_rwlock_rdlock.

This adds wake-ups that would be missing if assuming that for a
non-writer-preferring rwlock, if one thread has acquired a rdlock and
does not release it, another thread will eventually acquire a rdlock too
despite concurrent write lock acquisition attempts.  BZ 14958 is about
supporting this assumption.  Strictly speaking, this isn't a valid
test case, but nonetheless worth supporting (see comment 7 of BZ 14958).

1 files changed, 10 insertions, 2 deletions

diff --git a/nptl/pthread_rwlock_timedwrlock.c b/nptl/pthread_rwlock_timedwrlock.c
index a759fa9..c542534 100644
--- a/nptl/pthread_rwlock_timedwrlock.c
+++ b/nptl/pthread_rwlock_timedwrlock.c
@@ -141,8 +141,16 @@ pthread_rwlock_timedwrlock (rwlock, abstime)
 	  /* If we prefer writers, it can have happened that readers blocked
 	     for us to acquire the lock first.  If we have timed out, we need
 	     to wake such readers if there are any, and if there is no writer
-	     currently (otherwise, the writer will take care of wake-up).  */
-	  if (!PTHREAD_RWLOCK_PREFER_READER_P (rwlock)
+	     currently (otherwise, the writer will take care of wake-up).
+	     Likewise, even if we prefer readers, we can be responsible for
+	     wake-up (see pthread_rwlock_unlock) if no reader or writer has
+	     acquired the lock.  We have timed out and thus not consumed a
+	     futex wake-up; therefore, if there is no other blocked writer
+	     that would consume the wake-up and thus take over responsibility,
+	     we need to wake blocked readers.  */
+	  if ((!PTHREAD_RWLOCK_PREFER_READER_P (rwlock)
+	       || ((rwlock->__data.__nr_readers == 0)
+		   && (rwlock->__data.__nr_writers_queued == 0)))
 	      && (rwlock->__data.__nr_readers_queued > 0)
 	      && (rwlock->__data.__writer == 0))
 	    {