netdev - [PATCH 3/4] xfrm: avoid synchronize

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Message-ID: <20210423081409.729557-4-steffen.klassert@secunet.com>
Date:   Fri, 23 Apr 2021 10:14:08 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
CC:     Herbert Xu <herbert@...dor.apana.org.au>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        <netdev@...r.kernel.org>
Subject: [PATCH 3/4] xfrm: avoid synchronize_rcu during netns destruction

From: Florian Westphal <fw@...len.de>

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>
Signed-off-by: Steffen Klassert <steffen.klassert@...unet.com>
---
 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 df8bc8fc724c..f0aecee4d539 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,
 };
 
-- 
2.25.1