diff options
| author | Sowmini Varadhan <sowmini.varadhan@oracle.com> | 2016-06-05 00:00:00 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2016-06-08 01:10:15 +0300 |
| commit | 9c79440e2c5e2518879f1599270f64c3ddda3baf (patch) | |
| tree | 69cbc888d7d91fe1e3c197443f608e35d54a4c30 /net/rds/tcp.c | |
| parent | 0b6f760cff04a7cdfafc3ec6915e91fed0533d8d (diff) | |
| download | linux-9c79440e2c5e2518879f1599270f64c3ddda3baf.tar.xz | |
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@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/rds/tcp.c')
| -rw-r--r-- | net/rds/tcp.c | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/net/rds/tcp.c b/net/rds/tcp.c index 7ab1b41ffc88..74ee126a6fe6 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) { |