From: Sowmini Varadhan <sowmini.varadhan@oracle.com>
To: chien.yen@oracle.com, davem@davemloft.net
Cc: rds-devel@oss.oracle.com, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, sowmini.varadhan@oracle.com,
chuck.lever@oracle.com
Subject: [PATCH] rds: rds_cong_queue_updates needs to defer the congestion update transmission
Date: Tue, 10 Feb 2015 09:22:14 -0500 [thread overview]
Message-ID: <20150210142214.GO337@oracle.com> (raw)
This patch fixes a sock_lock deadlock in the rds_cong_queue_update path.
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.
Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
---
net/rds/cong.c | 16 +++++++++++++++-
1 files changed, 15 insertions(+), 1 deletions(-)
diff --git a/net/rds/cong.c b/net/rds/cong.c
index e5b65ac..765d18f 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:
+ * 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 rds_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);
}
}
--
1.7.1
next reply other threads:[~2015-02-10 14:22 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-10 14:22 Sowmini Varadhan [this message]
2015-02-10 16:50 ` [PATCH] rds: rds_cong_queue_updates needs to defer the congestion update transmission Chuck Lever
2015-02-10 16:56 ` Sowmini Varadhan
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