Patch "net: add exit_batch_rtnl() method" has been added to the 6.6-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    net: add exit_batch_rtnl() method

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net-add-exit_batch_rtnl-method.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit fde7ab53d3e6e261b77704d4be0d4f8dd0c034a0
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
Date:   Tue Feb 6 14:42:57 2024 +0000

    net: add exit_batch_rtnl() method
    
    [ Upstream commit fd4f101edbd9f99567ab2adb1f2169579ede7c13 ]
    
    Many (struct pernet_operations)->exit_batch() methods have
    to acquire rtnl.
    
    In presence of rtnl mutex pressure, this makes cleanup_net()
    very slow.
    
    This patch adds a new exit_batch_rtnl() method to reduce
    number of rtnl acquisitions from cleanup_net().
    
    exit_batch_rtnl() handlers are called while rtnl is locked,
    and devices to be killed can be queued in a list provided
    as their second argument.
    
    A single unregister_netdevice_many() is called right
    before rtnl is released.
    
    exit_batch_rtnl() handlers are called before ->exit() and
    ->exit_batch() handlers.
    
    Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
    Reviewed-by: Antoine Tenart <atenart@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240206144313.2050392-2-edumazet@xxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Stable-dep-of: 46841c7053e6 ("gtp: Use for_each_netdev_rcu() in gtp_genl_dump_pdp().")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 958c805df1915..1befad79a6734 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -442,6 +442,9 @@ struct pernet_operations {
 	void (*pre_exit)(struct net *net);
 	void (*exit)(struct net *net);
 	void (*exit_batch)(struct list_head *net_exit_list);
+	/* Following method is called with RTNL held. */
+	void (*exit_batch_rtnl)(struct list_head *net_exit_list,
+				struct list_head *dev_kill_list);
 	unsigned int *id;
 	size_t size;
 };
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 92b7fea4d495c..70ac9d9bc8770 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -321,8 +321,9 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
 {
 	/* Must be called with pernet_ops_rwsem held */
 	const struct pernet_operations *ops, *saved_ops;
-	int error = 0;
 	LIST_HEAD(net_exit_list);
+	LIST_HEAD(dev_kill_list);
+	int error = 0;
 
 	refcount_set(&net->ns.count, 1);
 	ref_tracker_dir_init(&net->refcnt_tracker, 128, "net refcnt");
@@ -360,6 +361,15 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
 
 	synchronize_rcu();
 
+	ops = saved_ops;
+	rtnl_lock();
+	list_for_each_entry_continue_reverse(ops, &pernet_list, list) {
+		if (ops->exit_batch_rtnl)
+			ops->exit_batch_rtnl(&net_exit_list, &dev_kill_list);
+	}
+	unregister_netdevice_many(&dev_kill_list);
+	rtnl_unlock();
+
 	ops = saved_ops;
 	list_for_each_entry_continue_reverse(ops, &pernet_list, list)
 		ops_exit_list(ops, &net_exit_list);
@@ -588,6 +598,7 @@ static void cleanup_net(struct work_struct *work)
 	struct net *net, *tmp, *last;
 	struct llist_node *net_kill_list;
 	LIST_HEAD(net_exit_list);
+	LIST_HEAD(dev_kill_list);
 
 	/* Atomically snapshot the list of namespaces to cleanup */
 	net_kill_list = llist_del_all(&cleanup_list);
@@ -628,6 +639,14 @@ static void cleanup_net(struct work_struct *work)
 	 */
 	synchronize_rcu();
 
+	rtnl_lock();
+	list_for_each_entry_reverse(ops, &pernet_list, list) {
+		if (ops->exit_batch_rtnl)
+			ops->exit_batch_rtnl(&net_exit_list, &dev_kill_list);
+	}
+	unregister_netdevice_many(&dev_kill_list);
+	rtnl_unlock();
+
 	/* Run all of the network namespace exit methods */
 	list_for_each_entry_reverse(ops, &pernet_list, list)
 		ops_exit_list(ops, &net_exit_list);
@@ -1170,7 +1189,17 @@ static void free_exit_list(struct pernet_operations *ops, struct list_head *net_
 {
 	ops_pre_exit_list(ops, net_exit_list);
 	synchronize_rcu();
+
+	if (ops->exit_batch_rtnl) {
+		LIST_HEAD(dev_kill_list);
+
+		rtnl_lock();
+		ops->exit_batch_rtnl(net_exit_list, &dev_kill_list);
+		unregister_netdevice_many(&dev_kill_list);
+		rtnl_unlock();
+	}
 	ops_exit_list(ops, net_exit_list);
+
 	ops_free_list(ops, net_exit_list);
 }