netdev - [PATCH ipsec-next 3/3] xfrm: avoid synchronize

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Date:   Wed, 14 Apr 2021 18:12:53 +0200
From:   Florian Westphal <fw@...len.de>
To:     <netdev@...r.kernel.org>
Cc:     steffen.klassert@...unet.com, davem@...emloft.net, kuba@...nel.org,
        herbert@...dor.apana.org.au, Florian Westphal <fw@...len.de>
Subject: [PATCH ipsec-next 3/3] xfrm: avoid synchronize_rcu during netns destruction

Use the new exit_pre hook to NULL the netlink socket.
The net namespace core will do a synchronize_rcu() between the exit_pre
and exit/exit_batch handlers.

Signed-off-by: Florian Westphal <fw@...len.de>
---
 net/xfrm/xfrm_user.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 5a0ef4361e43..9313592fa01f 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -3480,18 +3480,22 @@ static int __net_init xfrm_user_net_init(struct net *net)
 	return 0;
 }
 
+static void __net_exit xfrm_user_net_pre_exit(struct net *net)
+{
+	RCU_INIT_POINTER(net->xfrm.nlsk, NULL);
+}
+
 static void __net_exit xfrm_user_net_exit(struct list_head *net_exit_list)
 {
 	struct net *net;
-	list_for_each_entry(net, net_exit_list, exit_list)
-		RCU_INIT_POINTER(net->xfrm.nlsk, NULL);
-	synchronize_net();
+
 	list_for_each_entry(net, net_exit_list, exit_list)
 		netlink_kernel_release(net->xfrm.nlsk_stash);
 }
 
 static struct pernet_operations xfrm_user_net_ops = {
 	.init	    = xfrm_user_net_init,
+	.pre_exit   = xfrm_user_net_pre_exit,
 	.exit_batch = xfrm_user_net_exit,
 };
 
-- 
2.26.3