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 <[email protected]>
---
changes from v1: incorporate feedback from Chuck Lever
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 (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);
}
}
--
1.7.1
From: Sowmini Varadhan <[email protected]>
Date: Tue, 10 Feb 2015 13:33:37 -0500
>
> 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 <[email protected]>
Applied.