From 9c79440e2c5e2518879f1599270f64c3ddda3baf Mon Sep 17 00:00:00 2001 From: Sowmini Varadhan Date: Sat, 4 Jun 2016 14:00:00 -0700 Subject: RDS: TCP: fix race windows in send-path quiescence by rds_tcp_accept_one() The send path needs to be quiesced before resetting callbacks from rds_tcp_accept_one(), and commit eb192840266f ("RDS:TCP: Synchronize rds_tcp_accept_one with rds_send_xmit when resetting t_sock") achieves this using the c_state and RDS_IN_XMIT bit following the pattern used by rds_conn_shutdown(). However this leaves the possibility of a race window as shown in the sequence below take t_conn_lock in rds_tcp_conn_connect send outgoing syn to peer drop t_conn_lock in rds_tcp_conn_connect incoming from peer triggers rds_tcp_accept_one, conn is marked CONNECTING wait for RDS_IN_XMIT to quiesce any rds_send_xmit threads call rds_tcp_reset_callbacks [.. race-window where incoming syn-ack can cause the conn to be marked UP from rds_tcp_state_change ..] lock_sock called from rds_tcp_reset_callbacks, and we set t_sock to null As soon as the conn is marked UP in the race-window above, rds_send_xmit() threads will proceed to rds_tcp_xmit and may encounter a null-pointer deref on the t_sock. Given that rds_tcp_state_change() is invoked in softirq context, whereas rds_tcp_reset_callbacks() is in workq context, and testing for RDS_IN_XMIT after lock_sock could result in a deadlock with tcp_sendmsg, this commit fixes the race by using a new c_state, RDS_TCP_RESETTING, which will prevent a transition to RDS_CONN_UP from rds_tcp_state_change(). Signed-off-by: Sowmini Varadhan Acked-by: Santosh Shilimkar Signed-off-by: David S. Miller --- net/rds/tcp_listen.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) (limited to 'net/rds/tcp_listen.c') diff --git a/net/rds/tcp_listen.c b/net/rds/tcp_listen.c index d9fe53675d95..686b1d03a558 100644 --- a/net/rds/tcp_listen.c +++ b/net/rds/tcp_listen.c @@ -135,16 +135,15 @@ int rds_tcp_accept_one(struct socket *sock) !conn->c_outgoing) { goto rst_nsk; } else { - atomic_set(&conn->c_state, RDS_CONN_CONNECTING); - wait_event(conn->c_waitq, - !test_bit(RDS_IN_XMIT, &conn->c_flags)); rds_tcp_reset_callbacks(new_sock, conn); conn->c_outgoing = 0; + /* rds_connect_path_complete() marks RDS_CONN_UP */ + rds_connect_path_complete(conn, RDS_CONN_DISCONNECTING); } } else { rds_tcp_set_callbacks(new_sock, conn); + rds_connect_path_complete(conn, RDS_CONN_CONNECTING); } - rds_connect_complete(conn); /* marks RDS_CONN_UP */ new_sock = NULL; ret = 0; goto out; -- cgit