rds: use RCU to synchronize work-enqueue with connection teardown

rds_sendmsg() can enqueue work on cp_send_w from process context, but
it should not enqueue this work if connection teardown  has commenced
(else we risk enquing work after rds_conn_path_destroy() has assumed that
all work has been cancelled/flushed).

Similarly some other functions like rds_cong_queue_updates
and rds_tcp_data_ready are called in softirq context, and may end
up enqueuing work on rds_wq after rds_conn_path_destroy() has assumed
that all workqs are quiesced.

Check the RDS_DESTROY_PENDING bit and use rcu synchronization to avoid
all these races.

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>

1 files changed, 4 insertions, 1 deletions

diff --git a/net/rds/tcp_send.c b/net/rds/tcp_send.c
index dc860d1bb608..73c74763ca72 100644
--- a/net/rds/tcp_send.c
+++ b/net/rds/tcp_send.c
@@ -202,8 +202,11 @@ void rds_tcp_write_space(struct sock *sk)
         tc->t_last_seen_una = rds_tcp_snd_una(tc);
         rds_send_path_drop_acked(cp, rds_tcp_snd_una(tc), rds_tcp_is_acked);
 
-        if ((refcount_read(&sk->sk_wmem_alloc) << 1) <= sk->sk_sndbuf)
+        rcu_read_lock();
+        if ((refcount_read(&sk->sk_wmem_alloc) << 1) <= sk->sk_sndbuf &&
+            !test_bit(RDS_DESTROY_PENDING, &cp->cp_flags))
                 queue_delayed_work(rds_wq, &cp->cp_send_w, 0);
+        rcu_read_unlock();
 
 out:
         read_unlock_bh(&sk->sk_callback_lock);