tcp: annotate data-races around tp->bytes_retrans

[ Upstream commit 5efc7b9 ]

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

Fixes: fb31c9b ("tcp: add data bytes retransmitted stats")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260416200319.3608680-9-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

@@ -4304,8 +4304,8 @@ struct sk_buff *tcp_get_timestamping_opt_stats(const struct sock *sk,
 
 	nla_put_u64_64bit(stats, TCP_NLA_BYTES_SENT, READ_ONCE(tp->bytes_sent),
 			  TCP_NLA_PAD);
-	nla_put_u64_64bit(stats, TCP_NLA_BYTES_RETRANS, tp->bytes_retrans,
-			  TCP_NLA_PAD);
+	nla_put_u64_64bit(stats, TCP_NLA_BYTES_RETRANS,
+			  READ_ONCE(tp->bytes_retrans), TCP_NLA_PAD);
 	nla_put_u32(stats, TCP_NLA_DSACK_DUPS, tp->dsack_dups);
 	nla_put_u32(stats, TCP_NLA_REORD_SEEN, tp->reord_seen);
 	nla_put_u32(stats, TCP_NLA_SRTT, tp->srtt_us >> 3);

net/ipv4/tcp_output.c

@@ -3414,7 +3414,7 @@ int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
 	WRITE_ONCE(tp->total_retrans, tp->total_retrans + segs);
-	tp->bytes_retrans += skb->len;
+	WRITE_ONCE(tp->bytes_retrans, tp->bytes_retrans + skb->len);
 
 	/* make sure skb->data is aligned on arches that require it
 	 * and check if ack-trimming & collapsing extended the headroom