From 80ad0d4a7a75158f2824d541e4802c88aba4f063 Mon Sep 17 00:00:00 2001 From: Sowmini Varadhan Date: Tue, 10 Feb 2015 13:33:37 -0500 Subject: [PATCH] rds: rds_cong_queue_updates needs to defer the congestion update transmission When the RDS transport is TCP, we cannot inline the call to rds_send_xmit from rds_cong_queue_update because (a) we are already holding the sock_lock in the recv path, and will deadlock when tcp_setsockopt/tcp_sendmsg try to get the sock lock (b) cong_queue_update does an irqsave on the rds_cong_lock, and this will trigger warnings (for a good reason) from functions called out of sock_lock. This patch reverts the change introduced by 2fa57129d ("RDS: Bypass workqueue when queueing cong updates"). The patch has been verified for both RDS/TCP as well as RDS/RDMA to ensure that there are not regressions for either transport: - for verification of RDS/TCP a client-server unit-test was used, with the server blocked in gdb and thus unable to drain its rcvbuf, eventually triggering a RDS congestion update. - for RDS/RDMA, the standard IB regression tests were used Signed-off-by: Sowmini Varadhan Signed-off-by: David S. Miller --- net/rds/cong.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/net/rds/cong.c b/net/rds/cong.c index e5b65acd650b..e6144b8246fd 100644 --- a/net/rds/cong.c +++ b/net/rds/cong.c @@ -221,7 +221,21 @@ void rds_cong_queue_updates(struct rds_cong_map *map) list_for_each_entry(conn, &map->m_conn_list, c_map_item) { if (!test_and_set_bit(0, &conn->c_map_queued)) { rds_stats_inc(s_cong_update_queued); - rds_send_xmit(conn); + /* We cannot inline the call to rds_send_xmit() here + * for two reasons (both pertaining to a TCP transport): + * 1. When we get here from the receive path, we + * are already holding the sock_lock (held by + * tcp_v4_rcv()). So inlining calls to + * tcp_setsockopt and/or tcp_sendmsg will deadlock + * when it tries to get the sock_lock()) + * 2. Interrupts are masked so that we can mark the + * the port congested from both send and recv paths. + * (See comment around declaration of rdc_cong_lock). + * An attempt to get the sock_lock() here will + * therefore trigger warnings. + * Defer the xmit to rds_send_worker() instead. + */ + queue_delayed_work(rds_wq, &conn->c_send_w, 0); } }