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 14:22:12 +0100
From:   Oliver Neukum <oneukum@...e.com>
To:     Ricardo Ribalda <ribalda@...omium.org>,
        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

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.

> 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()

	Regards
		Oliver