net: annotate sk->sk_rcvlowat lockless reads

sock_rcvlowat() or int_sk_rcvlowat() might be called without the socket
lock for example from tcp_poll().

Use READ_ONCE() to document the fact that other cpus might change
sk->sk_rcvlowat under us and avoid KCSAN splats.

Use WRITE_ONCE() on write sides too.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 888c92b63f5a..8781a92ea4b6 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1699,7 +1699,7 @@ int tcp_set_rcvlowat(struct sock *sk, int val)
         else
                 cap = sock_net(sk)->ipv4.sysctl_tcp_rmem[2] >> 1;
         val = min(val, cap);
-        sk->sk_rcvlowat = val ? : 1;
+        WRITE_ONCE(sk->sk_rcvlowat, val ? : 1);
 
         /* Check if we need to signal EPOLLIN right now */
         tcp_data_ready(sk);