1 files changed, 27 insertions, 0 deletions

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 02f660666ab8..1fefe6dcafd7 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -613,6 +613,33 @@ struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem)
         DEFINE_WAKE_Q(wake_q);
 
         /*
+        * __rwsem_down_write_failed_common(sem)
+        *   rwsem_optimistic_spin(sem)
+        *     osq_unlock(sem->osq)
+        *   ...
+        *   atomic_long_add_return(&sem->count)
+        *
+        *      - VS -
+        *
+        *              __up_write()
+        *                if (atomic_long_sub_return_release(&sem->count) < 0)
+        *                  rwsem_wake(sem)
+        *                    osq_is_locked(&sem->osq)
+        *
+        * And __up_write() must observe !osq_is_locked() when it observes the
+        * atomic_long_add_return() in order to not miss a wakeup.
+        *
+        * This boils down to:
+        *
+        * [S.rel] X = 1                [RmW] r0 = (Y += 0)
+        *         MB                         RMB
+        * [RmW]   Y += 1               [L]   r1 = X
+        *
+        * exists (r0=1 /\ r1=0)
+        */
+        smp_rmb();
+
+        /*
          * If a spinner is present, it is not necessary to do the wakeup.
          * Try to do wakeup only if the trylock succeeds to minimize
          * spinlock contention which may introduce too much delay in the