tcp: annotate data-races around tp->notsent_lowat

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>
Link: https://lore.kernel.org/r/20230719212857.3943972-10-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/tcp.h b/include/net/tcp.h
index a8b93b2..0ca972e 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -2061,7 +2061,11 @@ 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 5beec71..2b2241e 100644 (file)
--- 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;