tcp: Respect SO_RCVLOWAT in tcp_poll().

Based upon a report by Vito Caputo.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 4 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 1ab341e5d3e0..7d81a1ee5507 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -384,13 +384,17 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
 
         /* Connected? */
         if ((1 << sk->sk_state) & ~(TCPF_SYN_SENT | TCPF_SYN_RECV)) {
+                int target = sock_rcvlowat(sk, 0, INT_MAX);
+
+                if (tp->urg_seq == tp->copied_seq &&
+                    !sock_flag(sk, SOCK_URGINLINE) &&
+                    tp->urg_data)
+                        target--;
+
                 /* Potential race condition. If read of tp below will
                  * escape above sk->sk_state, we can be illegally awaken
                  * in SYN_* states. */
-                if ((tp->rcv_nxt != tp->copied_seq) &&
-                    (tp->urg_seq != tp->copied_seq ||
-                     tp->rcv_nxt != tp->copied_seq + 1 ||
-                     sock_flag(sk, SOCK_URGINLINE) || !tp->urg_data))
+                if (tp->rcv_nxt - tp->copied_seq >= target)
                         mask |= POLLIN | POLLRDNORM;
 
                 if (!(sk->sk_shutdown & SEND_SHUTDOWN)) {