Re: [PATCH net-next V3 2/7] netdevsim: Register devlink after device init

[Jakub Kicinski <kuba@kernel.org>]

On Fri, 5 Jun 2026 21:10:25 +0300 Mark Bloch wrote:
> devl_register() makes the devlink instance visible to userspace. A later
> patch also makes registration the point where devlink core may call
> eswitch_mode_set() to apply a boot-time default eswitch mode.
> 
> Move netdevsim registration after all objects (resources, params, regions,
> traps, debugfs etc) are initialized, and after the initial eswitch mode is
> set to legacy.
> 
> Move devl_unregister() to the beginning of nsim_drv_remove(), before those
> devlink objects are torn down. This keeps devlink register/unregister as
> the notification barrier and makes the later object teardown paths run
> after devlink is no longer registered, so they do not emit their own
> netlink DEL notifications.

This is going backwards. At some point someone from nVidia thought that
we can order our way out of locking, so mlx5 is likely ordered this way,
but this must not be required, or in any way normalized.
We (syzbot) quickly discovered that it doesn't cover all corner cases.
devl_lock() is exposed specifically to allow the driver to finish
whatever init it needs without letting user space invoke callbacks, yet.
Almost (?) all driver callbacks hold devl_lock(), so maybe the devlink
instance is "visible" to user space but that should not matter.