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

[Mark Bloch <mbloch@nvidia.com>]

On 11/06/2026 2:50, Jakub Kicinski wrote:
> 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.

Let me clarify.

No locking is changed here, and I don't want to make register/unregister
ordering a substitute for devl_lock().

The only requirement I have for this series is that devl_register() is called
only once the driver is ready for devlink core to call eswitch_mode_set().
That follows from the earlier direction to have the core apply the default
mode from devl_register() instead of adding an explicit driver call.

So if the objection is to the commit message wording, I can fix that and drop
the "notification barrier" language.

For unregister, I can probably leave the old ordering as-is. I moved it only
to mirror the register path, which felt cleaner, but it is not required for
the default-mode change and as the lock is held I see no issue with doing
that.

Mark