net: Add ->exit_rtnl() hook to struct pernet_operations.
struct pernet_operations provides two batching hooks; ->exit_batch()
and ->exit_batch_rtnl().
The batching variant is beneficial if ->exit() meets any of the
following conditions:
1) ->exit() repeatedly acquires a global lock for each netns
2) ->exit() has a time-consuming operation that can be factored
out (e.g. synchronize_rcu(), smp_mb(), etc)
3) ->exit() does not need to repeat the same iterations for each
netns (e.g. inet_twsk_purge())
Currently, none of the ->exit_batch_rtnl() functions satisfy any of
the above conditions because RTNL is factored out and held by the
caller and all of these functions iterate over the dying netns list.
Also, we want to hold per-netns RTNL there but avoid spreading
__rtnl_net_lock() across multiple locations.
Let's add ->exit_rtnl() hook and run it under __rtnl_net_lock().
The following patches will convert all ->exit_batch_rtnl() users
to ->exit_rtnl().
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/20250411205258.63164-4-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>