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From:   Ricardo Ribalda <ribalda@chromium.org>
Date:   Thu, 1 Dec 2022 14:34:16 +0100
Message-ID: <CANiDSCtm7dCst_atiWk=ZcK_D3=VzvD0+kWXVQr4gEn--JjGkw@mail.gmail.com>
Subject: Re: [PATCH v8 3/3] ASoC: SOF: Fix deadlock when shutdown a frozen userspace
To:     Oliver Neukum <oneukum@suse.com>
Cc:     Juergen Gross <jgross@suse.com>, Mark Brown <broonie@kernel.org>,
        Chromeos Kdump <chromeos-kdump@google.com>,
        Daniel Baluta <daniel.baluta@nxp.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Len Brown <len.brown@intel.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Ranjani Sridharan <ranjani.sridharan@linux.intel.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
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        Nicholas Piggin <npiggin@gmail.com>,
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        Eric Biederman <ebiederm@xmission.com>,
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Hi Oliver

On Thu, 1 Dec 2022 at 14:22, 'Oliver Neukum' via Chromeos Kdump
<chromeos-kdump@google.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