netdev - Re: Strangeness in ehea network driver's shutdown

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Message-ID: <CALJn8nN-5DZZkwrJurtT2NOUXGdEQa-aQt+MHvsii2oC_w5+FA@mail.gmail.com>
Date:   Tue, 6 Dec 2022 13:49:01 -0300
From:   "Guilherme G. Piccoli" <kernel@...ccoli.net>
To:     Jakub Kicinski <kuba@...nel.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Douglas Miller <dougmill@...ux.ibm.com>, netdev@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>, kernel@...gutronix.de,
        gpiccoli@...lia.com, cascardo@...onical.com
Subject: Re: Strangeness in ehea network driver's shutdown

On Mon, Oct 3, 2022 at 1:36 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Sat, 1 Oct 2022 16:31:31 +0200 Uwe Kleine-König wrote:
> > Hello,
> >
> > while doing some cleanup I stumbled over a problem in the ehea network
> > driver.
> >
> > In the driver's probe function (ehea_probe_adapter() via
> > ehea_register_memory_hooks()) a reboot notifier is registered. When this
> > notifier is triggered (ehea_reboot_notifier()) it unregisters the
> > driver. I'm unsure what is the order of the actions triggered by that.
> > Maybe the driver is unregistered twice if there are two bound devices?
> > Or the reboot notifier is called under a lock and unregistering the
> > driver (and so the devices) tries to unregister the notifier that is
> > currently locked and so results in a deadlock? Maybe Greg or Rafael can
> > tell about the details here?
> >
> > Whatever the effect is, it's strange. It makes me wonder why it's
> > necessary to free all the resources of the driver on reboot?! I don't
> > know anything about the specifics of the affected machines, but I guess
> > doing just the necessary stuff on reboot would be easier to understand,
> > quicker to execute and doesn't have such strange side effects.
> >
> > With my lack of knowledge about the machine, the best I can do is report
> > my findings. So don't expect a patch or testing from my side.
>
> Last meaningful commit to this driver FWIW:
>
> commit 29ab5a3b94c87382da06db88e96119911d557293
> Author: Guilherme G. Piccoli <kernel@...ccoli.net>
> Date:   Thu Nov 3 08:16:20 2016 -0200
>
> Also that's the last time we heard from Douglas AFAICT..

Hey folks, thanks for CCing me.

I've worked a bit with ehea some time ago, will need to dig up a bit
to understand things again.
But I'm cc'ing Cascardo - which have(/had?) a more deep knowledge on
that - in the hopes he can discuss the issue without requiring that
much study heh

Cheers,


Guilherme