rs_seen_congestion is read in rds_poll() and written in rds_sendmsg()
and rds_poll() without any lock.  Use READ_ONCE()/WRITE_ONCE() to
annotate these lockless accesses and silence KCSAN.

Fixes: b98ba52f96e7 ("RDS: only put sockets that have seen congestion on the poll_waitq")
Reported-by: syzbot+fbf3648ae7f5bdb05c59@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6a0f8d94.050a0220.6b33c.0000.GAE@google.com/
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
---
 net/rds/af_rds.c | 4 ++--
 net/rds/send.c   | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/rds/af_rds.c b/net/rds/af_rds.c
index 76f625986a7f..93b2da63ed42 100644
--- a/net/rds/af_rds.c
+++ b/net/rds/af_rds.c
@@ -219,7 +219,7 @@ static __poll_t rds_poll(struct file *file, struct socket *sock,
 
 	poll_wait(file, sk_sleep(sk), wait);
 
-	if (rs->rs_seen_congestion)
+	if (READ_ONCE(rs->rs_seen_congestion))
 		poll_wait(file, &rds_poll_waitq, wait);
 
 	read_lock_irqsave(&rs->rs_recv_lock, flags);
@@ -247,7 +247,7 @@ static __poll_t rds_poll(struct file *file, struct socket *sock,
 
 	/* clear state any time we wake a seen-congested socket */
 	if (mask)
-		rs->rs_seen_congestion = 0;
+		WRITE_ONCE(rs->rs_seen_congestion, 0);
 
 	return mask;
 }
diff --git a/net/rds/send.c b/net/rds/send.c
index d8b14ff9d366..e5d58c29aabe 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -1388,7 +1388,7 @@ int rds_sendmsg(struct socket *sock, struct msghdr *msg, size_t payload_len)
 
 	ret = rds_cong_wait(conn->c_fcong, dport, nonblock, rs);
 	if (ret) {
-		rs->rs_seen_congestion = 1;
+		WRITE_ONCE(rs->rs_seen_congestion, 1);
 		goto out;
 	}
 	while (!rds_send_queue_rm(rs, conn, cpath, rm, rs->rs_bound_port,
-- 
2.43.0