Re: [patch net] devlink: change per-devlink netdev notifier to static one

[Jakub Kicinski <kuba@kernel.org>]

On Wed, 10 May 2023 16:46:21 +0200 Jiri Pirko wrote:
> From: Jiri Pirko <jiri@nvidia.com>
> 
> The commit 565b4824c39f ("devlink: change port event netdev notifier
> from per-net to global") changed original per-net notifier to be
> per-devlink instance. That 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)
> 
> Steps to reproduce:
> $ modprobe mlx5_core
> $ ip netns add ns1
> $ devlink dev reload pci/0000:08:00.0 netns ns1
> $ ip netns del ns1
> 
> Resolve this by converting the notifier from per-devlink instance to
> a static one registered during init phase and leaving it registered
> forever. Use this notifier for all devlink port instances created
> later on.
> 
> Note what a tree needs this fix only in case all of the cited fixes
> commits are present.

Reviewed-by: Jakub Kicinski <kuba@kernel.org>

For posterity v1(/previous):
https://lore.kernel.org/all/20230509100939.760867-1-jiri@resnulli.us/