[PATCH net 09/14] tcp: annotate data-races around tp->dsack_dups

[Eric Dumazet <edumazet@google.com>]

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

Fixes: 7e10b6554ff2 ("tcp: add dsack blocks received stats")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/ipv4/tcp.c       | 2 +-
 net/ipv4/tcp_input.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 8c84639dc54bb8d8aa6f3eeb2b7c1fea16ebfcb5..57c4dcc8bfe948e895f713cadaad20409a9b8f14 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4465,7 +4465,7 @@ struct sk_buff *tcp_get_timestamping_opt_stats(const struct sock *sk,
 			  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_DSACK_DUPS, READ_ONCE(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);
 	nla_put_u16(stats, TCP_NLA_TIMEOUT_REHASH, tp->timeout_rehash);
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index edb5013873e0c4a9ba2f8a81a43eff5fb6e7a47b..65b3ecc6be4b57f97a62d0e5737a96ddb16dd14d 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1246,7 +1246,7 @@ static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq,
 	else if (tp->tlp_high_seq && tp->tlp_high_seq == end_seq)
 		state->flag |= FLAG_DSACK_TLP;
 
-	tp->dsack_dups += dup_segs;
+	WRITE_ONCE(tp->dsack_dups, tp->dsack_dups + dup_segs);
 	/* Skip the DSACK if dup segs weren't retransmitted by sender */
 	if (tp->dsack_dups > tp->total_retrans)
 		return 0;
-- 
2.54.0.rc1.513.gad8abe7a5a-goog