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/threads.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) (limited to 'net/rds/threads.c') diff --git a/net/rds/threads.c b/net/rds/threads.c index 454aa6d23327..4a323045719b 100644 --- a/net/rds/threads.c +++ b/net/rds/threads.c @@ -71,9 +71,9 @@ struct workqueue_struct *rds_wq; EXPORT_SYMBOL_GPL(rds_wq); -void rds_connect_complete(struct rds_connection *conn) +void rds_connect_path_complete(struct rds_connection *conn, int curr) { - if (!rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_UP)) { + if (!rds_conn_transition(conn, curr, RDS_CONN_UP)) { printk(KERN_WARNING "%s: Cannot transition to state UP, " "current state is %d\n", __func__, @@ -90,6 +90,12 @@ void rds_connect_complete(struct rds_connection *conn) queue_delayed_work(rds_wq, &conn->c_send_w, 0); queue_delayed_work(rds_wq, &conn->c_recv_w, 0); } +EXPORT_SYMBOL_GPL(rds_connect_path_complete); + +void rds_connect_complete(struct rds_connection *conn) +{ + rds_connect_path_complete(conn, RDS_CONN_CONNECTING); +} EXPORT_SYMBOL_GPL(rds_connect_complete); /* -- cgit v1.2.3-59-g8ed1b