[PATCH net 12/14] tcp: annotate data-races around tp->timeout_rehash

[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: 32efcc06d2a1 ("tcp: export count for rehash attempts")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/ipv4/tcp.c       | 3 ++-
 net/ipv4/tcp_timer.c | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 541bd0d2d8c4ed24934fd047dd46e532b30021be..192e95b71ce9868980a809184be83398d8740427 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4469,7 +4469,8 @@ struct sk_buff *tcp_get_timestamping_opt_stats(const struct sock *sk,
 	nla_put_u32(stats, TCP_NLA_DSACK_DUPS, READ_ONCE(tp->dsack_dups));
 	nla_put_u32(stats, TCP_NLA_REORD_SEEN, READ_ONCE(tp->reord_seen));
 	nla_put_u32(stats, TCP_NLA_SRTT, READ_ONCE(tp->srtt_us) >> 3);
-	nla_put_u16(stats, TCP_NLA_TIMEOUT_REHASH, tp->timeout_rehash);
+	nla_put_u16(stats, TCP_NLA_TIMEOUT_REHASH,
+		    READ_ONCE(tp->timeout_rehash));
 	nla_put_u32(stats, TCP_NLA_BYTES_NOTSENT,
 		    max_t(int, 0, tp->write_seq - tp->snd_nxt));
 	nla_put_u64_64bit(stats, TCP_NLA_EDT, orig_skb->skb_mstamp_ns,
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index ea99988795e7e87412eef2768c4471e90c3e873e..8d791a954cd6ced52380226f205c66224b8f8bbd 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -297,7 +297,7 @@ static int tcp_write_timeout(struct sock *sk)
 	}
 
 	if (sk_rethink_txhash(sk)) {
-		tp->timeout_rehash++;
+		WRITE_ONCE(tp->timeout_rehash, tp->timeout_rehash + 1);
 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTREHASH);
 	}
 
-- 
2.54.0.rc1.513.gad8abe7a5a-goog