[PATCH AUTOSEL 6.18-5.10] rds: annotate data-race around rs_seen_congestion

From: Jiayuan Chen <jiayuan.chen@linux.dev>

[ Upstream commit 67636cab273ed0c0b0f2adab6c9369a471cb7966 ]

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.

Reported-by: syzbot+fbf3648ae7f5bdb05c59@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6a0f8d94.050a0220.6b33c.0000.GAE@google.com/ (local)
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Reviewed-by: Allison Henderson <achender@kernel.org> 
Tested-by: Allison Henderson <achender@kernel.org>
Link: https://patch.msgid.link/20260522011621.304470-1-jiayuan.chen@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

The backport check finished: prepared stable commit `95ef1f3da4846`
(upstream `67636cab273ed`) exists on the `autosel` branch but is not in
current HEAD (`v6.18.44`), where the unannotated `rs_seen_congestion`
accesses are still present. That supports the **YES** backport
recommendation.

 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 cc3a898bf5d51..a9445937d225b 100644
--- a/net/rds/af_rds.c
+++ b/net/rds/af_rds.c

@@ -217,7 +217,7 @@ 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);

@@ -245,7 +245,7 @@ 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 071c5dca969a2..d474c9cda65ae 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c

@@ -1339,7 +1339,7 @@ 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,

-- 
2.53.0