[PATCH] tcp: possible race between tcp_done() and tcp_poll()

[Seiichi Ikarashi]

Similar to commit a4d258036ed9b2a1811.

Between receiving a packet and tcp_poll(), sk->sk_err is protected by memory 
barriers but
sk->sk_shutdown and sk->sk_state are not. So possibly, 
POLLIN|POLLRDNORM|POLLRDHUP might
not be set even when receiving a RST packet.

Signed-off-by: Seiichi Ikarashi <s.ikara...@jp.fujitsu.com>

 net/ipv4/tcp.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index cf45555..c8bc86e 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -456,6 +456,8 @@ unsigned int tcp_poll(struct file *file, struct socket 
*sock, poll_table *wait)
 
        sock_poll_wait(file, sk_sleep(sk), wait);
 
+       /* This barrier is coupled with smp_wmb() in tcp_reset() */
+       smp_rmb();
        state = sk_state_load(sk);
        if (state == TCP_LISTEN)
                return inet_csk_listen_poll(sk);
@@ -540,8 +542,6 @@ unsigned int tcp_poll(struct file *file, struct socket 
*sock, poll_table *wait)
                 */
                mask |= POLLOUT | POLLWRNORM;
        }
-       /* This barrier is coupled with smp_wmb() in tcp_reset() */
-       smp_rmb();
        if (sk->sk_err || !skb_queue_empty(&sk->sk_error_queue))
                mask |= POLLERR;
 
@@ -3291,6 +3291,9 @@ void tcp_done(struct sock *sk)
 
        sk->sk_shutdown = SHUTDOWN_MASK;
 
+       /* This barrier is coupled with smp_rmb() in tcp_poll() */
+       smp_wmb();
+
        if (!sock_flag(sk, SOCK_DEAD))
                sk->sk_state_change(sk);
        else