netdev - Re: [RFC PATCH net-next 1/2] devlink: Hold a reference on parent device

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Date: Thu, 22 Jun 2023 09:03:14 +0300
From: Ido Schimmel <idosch@...dia.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org,
	davem@...emloft.net, pabeni@...hat.com, edumazet@...gle.com,
	petrm@...dia.com
Subject: Re: [RFC PATCH net-next 1/2] devlink: Hold a reference on parent
 device

On Wed, Jun 21, 2023 at 12:03:57PM -0700, Jakub Kicinski wrote:
> Let's try to fix it at the netdevsim level then?

I think it's a good direction. I couldn't find a way to fix it in
devlink and the problem does seem specific to netdevsim.

> AFAIU we only need the bus to remain loaded for nsim_bus_dev_release
> to exist?

That's my understanding as well.

> What if we split netdevsim into two modules, put the bus stuff in a
> new module called netdevsim_bus, and leave the rest (driver) in just
> netdevsim. That way we can take a ref on netdevsim_bus until all
> devices are gone, and still load / unload netdevsim. With unload
> resulting in all devices getting auto-deleted.
> 
> I haven't looked in detail so maybe you'll immediately tell me it won't
> work, but I'm guessing this is how "real" buses work avoid the problem?

At least with PCI (which I believe is the bus backing most devlink
users), the release callback is builtin - not part of a module - so this
problem can't happen there.

Anyway, I will explore this direction.

Thanks!