From: Eric Dumazet <edumazet@google.com>
Date: Tue, 18 Jan 2022 11:43:40 +0000 (-0800)
Subject: netns: add schedule point in ops_exit_list()
X-Git-Tag: v4.19.226~14
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=4048cedfd16a995b2ef4294b9539da17e2fea750;p=thirdparty%2Fkernel%2Fstable.git

netns: add schedule point in ops_exit_list()

commit 2836615aa22de55b8fca5e32fe1b27a67cda625e upstream.

When under stress, cleanup_net() can have to dismantle
netns in big numbers. ops_exit_list() currently calls
many helpers [1] that have no schedule point, and we can
end up with soft lockups, particularly on hosts
with many cpus.

Even for moderate amount of netns processed by cleanup_net()
this patch avoids latency spikes.

[1] Some of these helpers like fib_sync_up() and fib_sync_down_dev()
are very slow because net/ipv4/fib_semantics.c uses host-wide hash tables,
and ifindex is used as the only input of two hash functions.
    ifindexes tend to be the same for all netns (lo.ifindex==1 per instance)
    This will be fixed in a separate patch.

Fixes: 72ad937abd0a ("net: Add support for batching network namespace cleanups")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 26d70c00b0545..3368624be5ecd 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -149,8 +149,10 @@ static void ops_exit_list(const struct pernet_operations *ops,
 {
 	struct net *net;
 	if (ops->exit) {
-		list_for_each_entry(net, net_exit_list, exit_list)
+		list_for_each_entry(net, net_exit_list, exit_list) {
 			ops->exit(net);
+			cond_resched();
+		}
 	}
 	if (ops->exit_batch)
 		ops->exit_batch(net_exit_list);