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, 5 insertions, 0 deletions

diff --git a/nptl/pthread_rwlock_unlock.c b/nptl/pthread_rwlock_unlock.c
index b8336f62bf..d2ad4b0375 100644
--- a/nptl/pthread_rwlock_unlock.c
+++ b/nptl/pthread_rwlock_unlock.c
@@ -40,8 +40,13 @@ __pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
     rwlock->__data.__writer = 0;
   else
     --rwlock->__data.__nr_readers;
+  /* If there are still readers present, we do not yet need to wake writers
+     nor are responsible to wake any readers.  */
   if (rwlock->__data.__nr_readers == 0)
     {
+      /* Note that if there is a blocked writer, we effectively make it
+	 responsible for waking any readers because we don't wake readers in
+	 this case.  */
       if (rwlock->__data.__nr_writers_queued)
 	{
 	  ++rwlock->__data.__writer_wakeup;