netdev - Re: [patch net 3/3] devlink: fix a deadlock with nested instances during namespace remove

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Date: Wed, 10 May 2023 08:11:41 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Jakub Kicinski <kuba@...nel.org>
Cc: netdev@...r.kernel.org, pabeni@...hat.com, davem@...emloft.net,
	edumazet@...gle.com, jacob.e.keller@...el.com, saeedm@...dia.com,
	moshe@...dia.com
Subject: Re: [patch net 3/3] devlink: fix a deadlock with nested instances
 during namespace remove

Wed, May 10, 2023 at 05:24:44AM CEST, kuba@...nel.org wrote:
>On Tue,  9 May 2023 12:09:36 +0200 Jiri Pirko wrote:
>> The commit 565b4824c39f ("devlink: change port event netdev notifier
>> from per-net to global") changed original per-net notifier to be global
>> which fixed the issue of non-receiving events of netdev uninit if that
>> moved to a different namespace. That worked fine in -net tree.
>> 
>> However, later on when commit ee75f1fc44dd ("net/mlx5e: Create
>> separate devlink instance for ethernet auxiliary device") and
>> commit 72ed5d5624af ("net/mlx5: Suspend auxiliary devices only in
>> case of PCI device suspend") were merged, a deadlock was introduced
>> when removing a namespace with devlink instance with another nested
>> instance.
>> 
>> Here there is the bad flow example resulting in deadlock with mlx5:
>> net_cleanup_work -> cleanup_net (takes down_read(&pernet_ops_rwsem) ->
>> devlink_pernet_pre_exit() -> devlink_reload() ->
>> mlx5_devlink_reload_down() -> mlx5_unload_one_devl_locked() ->
>> mlx5_detach_device() -> del_adev() -> mlx5e_remove() ->
>> mlx5e_destroy_devlink() -> devlink_free() ->
>> unregister_netdevice_notifier() (takes down_write(&pernet_ops_rwsem)
>
>Why don't we have a single, static notifier for all of devlink?
>Why the per device/per port notifiers?
>
>We have the devlink port pointer in struct net_device, resolving from
>a global event to the correct devlink instance is trivial.

Okay, that might work. Let me explore that.