netdev - [PATCH] rds: add missing barrier to release

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Date:   Wed, 10 Aug 2022 09:00:42 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     Santosh Shilimkar <santosh.shilimkar@...cle.com>
cc:     netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        rds-devel@....oracle.com
Subject: [PATCH] rds: add missing barrier to release_refill

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@...hat.com>
Cc: stable@...r.kernel.org

Index: linux-2.6/net/rds/ib_recv.c
===================================================================
--- linux-2.6.orig/net/rds/ib_recv.c
+++ linux-2.6/net/rds/ib_recv.c
@@ -363,6 +363,7 @@ 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