2 files changed, 14 insertions, 0 deletions

diff --git a/kernel/locking/rwsem-spinlock.c b/kernel/locking/rwsem-spinlock.c
index 2555ae15ec14..3a5048572065 100644
--- a/kernel/locking/rwsem-spinlock.c
+++ b/kernel/locking/rwsem-spinlock.c
@@ -85,6 +85,13 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
 
                 list_del(&waiter->list);
                 tsk = waiter->task;
+                /*
+                 * Make sure we do not wakeup the next reader before
+                 * setting the nil condition to grant the next reader;
+                 * otherwise we could miss the wakeup on the other
+                 * side and end up sleeping again. See the pairing
+                 * in rwsem_down_read_failed().
+                 */
                 smp_mb();
                 waiter->task = NULL;
                 wake_up_process(tsk);
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 2f7cc4076f50..82aba467564a 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -186,6 +186,13 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type)
                 waiter = list_entry(next, struct rwsem_waiter, list);
                 next = waiter->list.next;
                 tsk = waiter->task;
+                /*
+                 * Make sure we do not wakeup the next reader before
+                 * setting the nil condition to grant the next reader;
+                 * otherwise we could miss the wakeup on the other
+                 * side and end up sleeping again. See the pairing
+                 * in rwsem_down_read_failed().
+                 */
                 smp_mb();
                 waiter->task = NULL;
                 wake_up_process(tsk);