netdev - [PATCH RFC RFC] rds: Use NETDEV_UNREGISTER in rds_tcp_dev_event() (then kill NETDEV_UNREGISTER

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Date:   Fri, 16 Mar 2018 15:38:23 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     santosh.shilimkar@...cle.com, davem@...emloft.net,
        netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        rds-devel@....oracle.com, edumazet@...gle.com,
        ktkhai@...tuozzo.com, sowmini.varadhan@...cle.com
Subject: [PATCH RFC RFC] rds: Use NETDEV_UNREGISTER in rds_tcp_dev_event()
 (then kill NETDEV_UNREGISTER_FINAL)

Hi,

rds_tcp_dev_event() is the last user of NETDEV_UNREGISTER_FINAL stage.
If we rework it, we'll be able to kill the stage, and this will decrease
the number of rtnl_lock() we take during generic net device unregistration.
This is very hot path for namespaces.

467fa15356acf by Sowmini Varadhan added NETDEV_UNREGISTER_FINAL dependence
with the commentary:

	/* rds-tcp registers as a pernet subys, so the ->exit will only
	 * get invoked after network acitivity has quiesced. We need to
	 * clean up all sockets  to quiesce network activity, and use
	 * the unregistration of the per-net loopback device as a trigger
	 * to start that cleanup.
	 */

It seems all the protocols pernet subsystems meet this situation, but they
solve it in generic way. What does rds so specific have?

This commit makes event handler to iterate rds_tcp_conn_list and
kill them. If we change the stage to NETDEV_UNREGISTER, what will change?
Can unregistered loopback device on dead net add new items to rds_tcp_conn_list?
How it's possible?

What the problem is to move rds_tcp_kill_sock() into pernet subsys exit?

Kirill
---
 net/rds/tcp.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/rds/tcp.c b/net/rds/tcp.c
index eb04e7fa2467..4c6db9cb6261 100644
--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c
@@ -567,7 +567,7 @@ static int rds_tcp_dev_event(struct notifier_block *this,
 	 * the unregistration of the per-net loopback device as a trigger
 	 * to start that cleanup.
 	 */
-	if (event == NETDEV_UNREGISTER_FINAL &&
+	if (event == NETDEV_UNREGISTER &&
 	    dev->ifindex == LOOPBACK_IFINDEX)
 		rds_tcp_kill_sock(dev_net(dev));