net: add exit_batch_rtnl() method

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@google.com>
Reviewed-by: Antoine Tenart <atenart@kernel.org>
Link: https://lore.kernel.org/r/20240206144313.2050392-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index cd0c2eedbb5e..20c34bd7a077 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -448,6 +448,9 @@ 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;
 };