From: Omar Sandoval <osan...@fb.com>
We always do an atomic clear_bit() right before we call sbq_wake_up(),
so we can use smp_mb__after_atomic(). While we're here, comment the
memory barriers in here a little more.
Signed-off-by: Omar Sandoval <osan...@fb.com>
---
lib/sbitmap.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 2cecf05c82fd..df4e472df8a3 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -299,8 +299,14 @@ static void sbq_wake_up(struct sbitmap_queue *sbq)
struct sbq_wait_state *ws;
int wait_cnt;
- /* Ensure that the wait list checks occur after clear_bit(). */
- smp_mb();
+ /*
+ * Pairs with the memory barrier in set_current_state() to ensure the
+ * proper ordering of clear_bit()/waitqueue_active() in the waker and
+ * test_and_set_bit()/prepare_to_wait()/finish_wait() in the waiter. See
+ * the comment on waitqueue_active(). This is __after_atomic because we
+ * just did clear_bit() in the caller.
+ */
+ smp_mb__after_atomic();
ws = sbq_wake_ptr(sbq);
if (!ws)
@@ -331,7 +337,8 @@ void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
int i, wake_index;
/*
- * Make sure all changes prior to this are visible from other CPUs.
+ * Pairs with the memory barrier in set_current_state() like in
+ * sbq_wake_up().
*/
smp_mb();
wake_index = atomic_read(&sbq->wake_index);
--
2.11.0
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