[PATCH 179/241] RDS: fix rds-ping spinlock recursion

[Herton Ronaldo Krzesinski]

3.5.7.2 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: "jeff.liu" <jeff.liu at oracle.com>

commit 5175a5e76bbdf20a614fb47ce7a38f0f39e70226 upstream.

This is the revised patch for fixing rds-ping spinlock recursion
according to Venkat's suggestions.

RDS ping/pong over TCP feature has been broken for years(2.6.39 to
3.6.0) since we have to set TCP cork and call kernel_sendmsg() between
ping/pong which both need to lock "struct sock *sk". However, this
lock has already been hold before rds_tcp_data_ready() callback is
triggerred. As a result, we always facing spinlock resursion which
would resulting in system panic.

Given that RDS ping is only used to test the connectivity and not for
serious performance measurements, we can queue the pong transmit to
rds_wq as a delayed response.

Reported-by: Dan Carpenter <dan.carpenter at oracle.com>
CC: Venkat Venkatsubra <venkat.x.venkatsubra at oracle.com>
CC: David S. Miller <davem at davemloft.net>
CC: James Morris <james.l.morris at oracle.com>
Signed-off-by: Jie Liu <jeff.liu at oracle.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
---
 net/rds/send.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/rds/send.c b/net/rds/send.c
index 96531d4..88eace5 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -1122,7 +1122,7 @@ rds_send_pong(struct rds_connection *conn, __be16 dport)
 	rds_stats_inc(s_send_pong);
 
 	if (!test_bit(RDS_LL_SEND_FULL, &conn->c_flags))
-		rds_send_xmit(conn);
+		queue_delayed_work(rds_wq, &conn->c_send_w, 0);
 
 	rds_message_put(rm);
 	return 0;
-- 
1.7.9.5