From 7b4b000951f09cfe3604a6fdf5469894b4e75adb Mon Sep 17 00:00:00 2001 From: "santosh.shilimkar@oracle.com" Date: Fri, 16 Oct 2015 22:13:21 -0400 Subject: [PATCH] RDS: fix rds-ping deadlock over TCP transport Sowmini found hang with rds-ping while testing RDS over TCP. Its a corner case and doesn't happen always. The issue is not reproducible with IB transport. Its clear from below dump why we see it with RDS TCP. [] do_tcp_setsockopt+0xb5/0x740 [] tcp_setsockopt+0x24/0x30 [] sock_common_setsockopt+0x14/0x20 [] rds_tcp_xmit_prepare+0x5d/0x70 [rds_tcp] [] rds_send_xmit+0xd7/0x740 [rds] [] rds_send_pong+0x142/0x180 [rds] [] rds_recv_incoming+0x274/0x330 [rds] [] ? ttwu_queue+0x11e/0x130 [] ? skb_copy_bits+0x6d/0x2c0 [] rds_tcp_data_recv+0x2f0/0x3d0 [rds_tcp] [] tcp_read_sock+0x96/0x1c0 [] ? rds_tcp_recv_init+0x40/0x40 [rds_tcp] [] ? sock_def_write_space+0xa0/0xa0 [] rds_tcp_data_ready+0xa1/0xf0 [rds_tcp] [] tcp_data_queue+0x379/0x5b0 [] ? rds_tcp_write_space+0xbb/0x110 [rds_tcp] [] tcp_rcv_established+0x2e2/0x6e0 [] tcp_v4_do_rcv+0x122/0x220 [] tcp_v4_rcv+0x867/0x880 [] ip_local_deliver_finish+0xa3/0x220 This happens because rds_send_xmit() chain wants to take sock_lock which is already taken by tcp_v4_rcv() on its way to rds_tcp_data_ready(). Commit db6526dcb51b ("RDS: use rds_send_xmit() state instead of RDS_LL_SEND_FULL") which was trying to opportunistically finish the send request in same thread context. But because of above recursive lock hang with RDS TCP, the send work from rds_send_pong() needs to deferred to worker to avoid lock up. Given RDS ping is more of connectivity test than performance critical path, its should be ok even for transport like IB. Reported-by: Sowmini Varadhan Acked-by: Sowmini Varadhan Signed-off-by: Santosh Shilimkar Signed-off-by: Santosh Shilimkar Acked-by: Sowmini Varadhan Signed-off-by: David S. Miller --- net/rds/send.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/net/rds/send.c b/net/rds/send.c index ee49c2556f47..827155c2ead1 100644 --- a/net/rds/send.c +++ b/net/rds/send.c @@ -1182,9 +1182,8 @@ rds_send_pong(struct rds_connection *conn, __be16 dport) rds_stats_inc(s_send_queued); rds_stats_inc(s_send_pong); - ret = rds_send_xmit(conn); - if (ret == -ENOMEM || ret == -EAGAIN) - queue_delayed_work(rds_wq, &conn->c_send_w, 1); + /* schedule the send work on rds_wq */ + queue_delayed_work(rds_wq, &conn->c_send_w, 1); rds_message_put(rm); return 0; -- 2.20.1