tcp: annotate data-races around (tp->write_seq - tp->snd_nxt)

[ Upstream commit 3a63b3d ]

tcp_get_timestamping_opt_stats() intentionally runs lockless, we must
add READ_ONCE() annotations to keep KCSAN happy.

WRITE_ONCE() annotations are already present.

Fixes: e08ab0b ("tcp: add bytes not sent to SCM_TIMESTAMPING_OPT_STATS")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260416200319.3608680-14-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: edumazet

net/ipv4/tcp.c

@@ -4311,7 +4311,8 @@ struct sk_buff *tcp_get_timestamping_opt_stats(const struct sock *sk,
 	nla_put_u32(stats, TCP_NLA_SRTT, tp->srtt_us >> 3);
 	nla_put_u16(stats, TCP_NLA_TIMEOUT_REHASH, tp->timeout_rehash);
 	nla_put_u32(stats, TCP_NLA_BYTES_NOTSENT,
-		    max_t(int, 0, tp->write_seq - tp->snd_nxt));
+		    max_t(int, 0,
+			  READ_ONCE(tp->write_seq) - READ_ONCE(tp->snd_nxt)));
 	nla_put_u64_64bit(stats, TCP_NLA_EDT, orig_skb->skb_mstamp_ns,
 			  TCP_NLA_PAD);
 	if (ack_skb)