netdev - [PATCH net] tcp: do not report TCP_CM_INQ of 0 for closed connections

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Date:   Wed,  6 Mar 2019 13:01:36 -0500
From:   Soheil Hassas Yeganeh <soheil.kdev@...il.com>
To:     davem@...emloft.net, netdev@...r.kernel.org
Cc:     edumazet@...gle.com, ycheng@...gle.com, ncardwell@...gle.com,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: [PATCH net] tcp: do not report TCP_CM_INQ of 0 for closed connections

From: Soheil Hassas Yeganeh <soheil@...gle.com>

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@...gle.com>
Acked-by: Neal Cardwell <ncardwell@...gle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Acked-by: Yuchung Cheng <ycheng@...gle.com>
---
 net/ipv4/tcp.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index ad07dd71063da..8b25017e0dc93 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1933,6 +1933,11 @@ 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;
 }

-- 
2.21.0.352.gf09ad66450-goog