[PATCH 4.14 177/229] rds: add missing barrier to release_refill

Greg Kroah-Hartman
2022-08-23T10:12:29Z

From: Mikulas Patocka <mpatocka@redhat.com>

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@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/rds/ib_recv.c | 1 +
1 file changed, 1 insertion(+)

--- a/net/rds/ib_recv.c
+++ b/net/rds/ib_recv.c
@@ -362,6 +362,7 @@ 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