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

[Ricardo Ribalda]

Hi Oliver

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