[PATCH 4.9 067/101] rds: add missing barrier to release_refill

[Greg Kroah-Hartman]

From: Mikulas Patocka <mpatocka@xxxxxxxxxx>

commit 9f414eb409daf4f778f011cf8266d36896bb930b upstream.

The functions clear_bit and set_bit do not imply a memory barrier, thus it
may be possible that the waitqueue_active function (which does not take
any locks) is moved before clear_bit and it could miss a wakeup event.

Fix this bug by adding a memory barrier after clear_bit.

Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/rds/ib_recv.c |    1 +
 1 file changed, 1 insertion(+)

--- a/net/rds/ib_recv.c
+++ b/net/rds/ib_recv.c
@@ -356,6 +356,7 @@ static int acquire_refill(struct rds_con
 static void release_refill(struct rds_connection *conn)
 {
 	clear_bit(RDS_RECV_REFILL, &conn->c_flags);
+	smp_mb__after_atomic();
 
 	/* We don't use wait_on_bit()/wake_up_bit() because our waking is in a
 	 * hot path and finding waiters is very rare.  We don't want to walk