[PATCH net 09/11] tcp: annotate data-races around tp->notsent_lowat

[Eric Dumazet <edumazet@google.com>]

tp->notsent_lowat can be read locklessly from do_tcp_getsockopt()
and tcp_poll().

Fixes: c9bee3b7fdec ("tcp: TCP_NOTSENT_LOWAT socket option")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/net/tcp.h | 6 +++++-
 net/ipv4/tcp.c    | 4 ++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 855dbe72e431776257037d75e32037b44905453c..a32d1963cb75ff81c164b3021a848d3d29816642 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -2059,7 +2059,11 @@ void __tcp_v4_send_check(struct sk_buff *skb, __be32 saddr, __be32 daddr);
 static inline u32 tcp_notsent_lowat(const struct tcp_sock *tp)
 {
 	struct net *net = sock_net((struct sock *)tp);
-	return tp->notsent_lowat ?: READ_ONCE(net->ipv4.sysctl_tcp_notsent_lowat);
+	u32 val;
+
+	val = READ_ONCE(tp->notsent_lowat);
+
+	return val ?: READ_ONCE(net->ipv4.sysctl_tcp_notsent_lowat);
 }
 
 bool tcp_stream_memory_free(const struct sock *sk, int wake);
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 5beec71a5c418db65e19eb2a68ffd839d4550efc..2b2241e9b492726562a6b5055cf8c168e5fed799 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3664,7 +3664,7 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 		err = tcp_repair_set_window(tp, optval, optlen);
 		break;
 	case TCP_NOTSENT_LOWAT:
-		tp->notsent_lowat = val;
+		WRITE_ONCE(tp->notsent_lowat, val);
 		sk->sk_write_space(sk);
 		break;
 	case TCP_INQ:
@@ -4164,7 +4164,7 @@ int do_tcp_getsockopt(struct sock *sk, int level,
 		val = tcp_time_stamp_raw() + READ_ONCE(tp->tsoffset);
 		break;
 	case TCP_NOTSENT_LOWAT:
-		val = tp->notsent_lowat;
+		val = READ_ONCE(tp->notsent_lowat);
 		break;
 	case TCP_INQ:
 		val = tp->recvmsg_inq;
-- 
2.41.0.255.g8b1d071c50-goog