linux-kernel - Re: [PATCH v8 3/3] ASoC: SOF: Fix deadlock when shutdown a frozen userspace

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Date:   Thu, 1 Dec 2022 14:34:16 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Oliver Neukum <oneukum@...e.com>
Cc:     Juergen Gross <jgross@...e.com>, Mark Brown <broonie@...nel.org>,
        Chromeos Kdump <chromeos-kdump@...gle.com>,
        Daniel Baluta <daniel.baluta@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Len Brown <len.brown@...el.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Eric Biederman <ebiederm@...ssion.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Joel Fernandes <joel@...lfernandes.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Peter Ujfalusi <peter.ujfalusi@...ux.intel.com>,
        Pavel Machek <pavel@....cz>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Ingo Molnar <mingo@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Dexuan Cui <decui@...rosoft.com>,
        Takashi Iwai <tiwai@...e.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        kexec@...ts.infradead.org, alsa-devel@...a-project.org,
        stable@...r.kernel.org, sound-open-firmware@...a-project.org,
        linuxppc-dev@...ts.ozlabs.org, linux-hyperv@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v8 3/3] ASoC: SOF: Fix deadlock when shutdown a frozen userspace

Hi Oliver

On Thu, 1 Dec 2022 at 14:22, 'Oliver Neukum' via Chromeos Kdump
<chromeos-kdump@...gle.com> wrote:
>
> On 01.12.22 14:03, Ricardo Ribalda wrote:
>
> Hi,
>
> > This patchset does not modify this behaviour. It simply fixes the
> > stall for kexec().
> >
> > The  patch that introduced the stall:
> > 83bfc7e793b5 ("ASoC: SOF: core: unregister clients and machine drivers
> > in .shutdown")
>
> That patch is problematic. I would go as far as saying that
> it needs to be reverted.
>

It fixes a real issue. We have not had any complaints until we tried
to kexec in the platform.
I wont recommend reverting it until we have an alternative implementation.

kexec is far less common than suspend/reboot.

> > was sent as a generalised version of:
> > https://github.com/thesofproject/linux/pull/3388
> >
> > AFAIK, we would need a similar patch for every single board.... which
> > I am not sure it is doable in a reasonable timeframe.
> >
> > On the meantime this seems like a decent compromises. Yes, a
> > miss-behaving userspace can still stall during suspend, but that was
> > not introduced in this patch.
>
> Well, I mean if you know what wrong then I'd say at least return to
> a sanely broken state.
>
> The whole approach is wrong. You need to be able to deal with user
> space talking to removed devices by returning an error and keeping
> the resources association with the open file allocated until
> user space calls close()

In general, the whole shutdown is broken for all the subsystems ;).
It is a complicated issue. Users handling fds, devices with DMAs in
the middle of an operation, dma fences....

Unfortunately I am not that familiar with the sound subsystem to make
a proper patch for this.

>
>         Regards
>                 Oliver
>
>
>
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-- 
Ricardo Ribalda