From 241b271952eb319622a6cc740a72abe41fc27ad6 Mon Sep 17 00:00:00 2001 From: Sowmini Varadhan Date: Sun, 11 Oct 2015 16:49:44 -0400 Subject: [PATCH] RDS-TCP: Reset tcp callbacks if re-using an outgoing socket in rds_tcp_accept_one() Consider the following "duelling syn" sequence between two peers A and B: A B SYN1 --> <-- SYN2 SYN2ACK --> Note that the SYN/ACK has already been sent out by TCP before rds_tcp_accept_one() gets invoked as part of callbacks. If the inet_addr(A) is numerically less than inet_addr(B), the arbitration scheme in rds_tcp_accept_one() will prefer the TCP connection triggered by SYN1, and will send a CLOSE for the SYN2 (just after the SYN2ACK was sent). Since B also follows the same arbitration scheme, it will send the SYN-ACK for SYN1 that will set up a healthy ESTABLISHED connection on both sides. B will also get a CLOSE for SYN2, which should result in the cleanup of the TCP state machine for SYN2, but it should not trigger any stale RDS-TCP callbacks (such as ->writespace, ->state_change etc), that would disrupt the progress of the SYN2 based RDS-TCP connection. Thus the arbitration scheme in rds_tcp_accept_one() should restore rds_tcp callbacks for the winner before setting them up for the new accept socket, and also make sure that conn->c_outgoing is set to 0 so that we do not trigger any reconnect attempts on the passive side of the tcp socket in the future, in conformance with commit c82ac7e69efe ("net/rds: RDS-TCP: only initiate reconnect attempt on outgoing TCP socket.") Signed-off-by: Sowmini Varadhan Acked-by: Santosh Shilimkar Signed-off-by: David S. Miller --- net/rds/tcp_listen.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/rds/tcp_listen.c b/net/rds/tcp_listen.c index 1d90240e5d82..0936a4a32b47 100644 --- a/net/rds/tcp_listen.c +++ b/net/rds/tcp_listen.c @@ -125,6 +125,9 @@ int rds_tcp_accept_one(struct socket *sock) new_sock = NULL; ret = 0; goto out; + } else if (rs_tcp->t_sock) { + rds_tcp_restore_callbacks(rs_tcp->t_sock, rs_tcp); + conn->c_outgoing = 0; } rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_CONNECTING);