tcp: do not report TCP_CM_INQ of 0 for closed connections

Returning 0 as inq to userspace indicates there is no more data to
read, and the application needs to wait for EPOLLIN. For a connection
that has received FIN from the remote peer, however, the application
must continue reading until getting EOF (return value of 0
from tcp_recvmsg) or an error, if edge-triggered epoll (EPOLLET) is
being used. Otherwise, the application will never receive a new
EPOLLIN, since there is no epoll edge after the FIN.

Return 1 when there is no data left on the queue but the
connection has received FIN, so that the applications continue
reading.

Fixes: b75eba76d3d72 (tcp: send in-queue bytes in cmsg upon read)
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index dbb08140cdc95916fefbc7fb1178aa4d249c91e9..6baa6dc1b13b0b94b1da238668b93e167cf444fe 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1937,6 +1937,11 @@ static int tcp_inq_hint(struct sock *sk)
                inq = tp->rcv_nxt - tp->copied_seq;
                release_sock(sk);
        }
+       /* After receiving a FIN, tell the user-space to continue reading
+        * by returning a non-zero inq.
+        */
+       if (inq == 0 && sock_flag(sk, SOCK_DONE))
+               inq = 1;
        return inq;
 }