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Date: Sat, 4 Jun 2016 14:00:00 -0700
From: Sowmini Varadhan <sowmini.varadhan@...cle.com>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net, rds-devel@....oracle.com,
ajaykumar.hotchandani@...cle.com, santosh.shilimkar@...cle.com,
sowmini.varadhan@...cle.com
Subject: [PATCH net 3/3] 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 <sowmini.varadhan@...cle.com>
---
net/rds/rds.h | 2 ++
net/rds/tcp.c | 14 +++++++++++++-
net/rds/tcp_connect.c | 2 +-
net/rds/tcp_listen.c | 7 +++----
net/rds/threads.c | 10 ++++++++--
5 files changed, 27 insertions(+), 8 deletions(-)
diff --git a/net/rds/rds.h b/net/rds/rds.h
index 80256b0..387df5f 100644
--- a/net/rds/rds.h
+++ b/net/rds/rds.h
@@ -74,6 +74,7 @@ enum {
RDS_CONN_CONNECTING,
RDS_CONN_DISCONNECTING,
RDS_CONN_UP,
+ RDS_CONN_RESETTING,
RDS_CONN_ERROR,
};
@@ -813,6 +814,7 @@ void rds_connect_worker(struct work_struct *);
void rds_shutdown_worker(struct work_struct *);
void rds_send_worker(struct work_struct *);
void rds_recv_worker(struct work_struct *);
+void rds_connect_path_complete(struct rds_connection *conn, int curr);
void rds_connect_complete(struct rds_connection *conn);
/* transport.c */
diff --git a/net/rds/tcp.c b/net/rds/tcp.c
index 7ab1b41..74ee126 100644
--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c
@@ -148,11 +148,23 @@ void rds_tcp_reset_callbacks(struct socket *sock,
* potentially have transitioned to the RDS_CONN_UP state,
* so we must quiesce any send threads before resetting
* c_transport_data. We quiesce these threads by setting
- * cp_state to something other than RDS_CONN_UP, and then
+ * c_state to something other than RDS_CONN_UP, and then
* waiting for any existing threads in rds_send_xmit to
* complete release_in_xmit(). (Subsequent threads entering
* rds_send_xmit() will bail on !rds_conn_up().
+ *
+ * However an incoming syn-ack at this point would end up
+ * marking the conn as RDS_CONN_UP, and would again permit
+ * rds_send_xmi() threads through, so ideally we would
+ * synchronize on RDS_CONN_UP after lock_sock(), but cannot
+ * do that: waiting on !RDS_IN_XMIT after lock_sock() may
+ * end up deadlocking with tcp_sendmsg(), and the RDS_IN_XMIT
+ * would not get set. As a result, we set c_state to
+ * RDS_CONN_RESETTTING, to ensure that rds_tcp_state_change
+ * cannot mark rds_conn_path_up() in the window before lock_sock()
*/
+ atomic_set(&conn->c_state, RDS_CONN_RESETTING);
+ wait_event(conn->c_waitq, !test_bit(RDS_IN_XMIT, &conn->c_flags));
lock_sock(osock->sk);
/* reset receive side state for rds_tcp_data_recv() for osock */
if (tc->t_tinc) {
diff --git a/net/rds/tcp_connect.c b/net/rds/tcp_connect.c
index fb82e0a..fba13d0 100644
--- a/net/rds/tcp_connect.c
+++ b/net/rds/tcp_connect.c
@@ -60,7 +60,7 @@ void rds_tcp_state_change(struct sock *sk)
case TCP_SYN_RECV:
break;
case TCP_ESTABLISHED:
- rds_connect_complete(conn);
+ rds_connect_path_complete(conn, RDS_CONN_CONNECTING);
break;
case TCP_CLOSE_WAIT:
case TCP_CLOSE:
diff --git a/net/rds/tcp_listen.c b/net/rds/tcp_listen.c
index d9fe536..686b1d0 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;
diff --git a/net/rds/threads.c b/net/rds/threads.c
index 454aa6d..4a32304 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);
/*
--
1.7.1
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