linux-kernel - Re: [PATCH v3 0/2] ALSA: core: Fix deadlock when shutdown a frozen userspace

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Message-ID: <CANiDSCtSAM3seszVWfjJPaYFO3v223P-tYEtdpW4+pQQ3bcf0g@mail.gmail.com>
Date:   Mon, 28 Nov 2022 10:26:36 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Takashi Iwai <tiwai@...e.com>, Len Brown <len.brown@...el.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>, Pavel Machek <pavel@....cz>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        alsa-devel@...a-project.org,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 0/2] ALSA: core: Fix deadlock when shutdown a frozen userspace

Hi Takashi

Thanks for your prompt reply

On Mon, 28 Nov 2022 at 10:24, Takashi Iwai <tiwai@...e.de> wrote:
>
> On Mon, 28 Nov 2022 10:10:12 +0100,
> Ricardo Ribalda wrote:
> >
> > Since 83bfc7e793b5 ("ASoC: SOF: core: unregister clients and machine drivers in .shutdown")
> > we wait for userspace to close its fds.
>
> IMO, the fix above brought more problem.  If you'd need to want to
> avoid later accesses during shutdown, the driver should rather just
> disconnect devices without waiting for the user-space completion.
> And, for that, a simple call of snd_card_disconnect() should suffice.
>
> > But that will never occur with a frozen userspace (like during kexec()).
> >
> > Lets detect the frozen userpace and act accordingly.
>
> ... and skipping the user-space sync at snd_card_disconnect_sync() as
> of this patch set is a dangerous move, I'm afraid.  The user-space
> gets frozen also at the normal suspend/resume, and it implies that the
> sync will be lost even for the normal PM, too (although it must be a
> very corner case).
>

And what about checking kexec_in_progress instead?

Thanks!

>
> thanks,
>
> Takashi
>
> >
> > To: Jaroslav Kysela <perex@...ex.cz>
> > To: Takashi Iwai <tiwai@...e.com>
> > To: "Rafael J. Wysocki" <rafael@...nel.org>
> > To: Pavel Machek <pavel@....cz>
> > To: Len Brown <len.brown@...el.com>
> > To: Kai Vehmanen <kai.vehmanen@...ux.intel.com>
> > To: Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>
> > To: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
> > To: Mark Brown <broonie@...nel.org>
> > Cc: alsa-devel@...a-project.org
> > Cc: linux-kernel@...r.kernel.org
> > Cc: "Joel Fernandes (Google)" <joel@...lfernandes.org>
> > Cc: linux-pm@...r.kernel.org
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > ---
> > Changes in v3:
> > - Wrap pm_freezing in a function
> > - Link to v2: https://lore.kernel.org/r/20221127-snd-freeze-v2-0-d8a425ea9663@chromium.org
> >
> > Changes in v2:
> > - Only use pm_freezing if CONFIG_FREEZER
> > - Link to v1: https://lore.kernel.org/r/20221127-snd-freeze-v1-0-57461a366ec2@chromium.org
> >
> > ---
> > Ricardo Ribalda (2):
> >       freezer: Add processes_frozen()
> >       ALSA: core: Fix deadlock when shutdown a frozen userspace
> >
> >  include/linux/freezer.h |  2 ++
> >  kernel/freezer.c        | 11 +++++++++++
> >  sound/core/init.c       | 13 +++++++++++++
> >  3 files changed, 26 insertions(+)
> > ---
> > base-commit: 4312098baf37ee17a8350725e6e0d0e8590252d4
> > change-id: 20221127-snd-freeze-1ee143228326
> >
> > Best regards,
> > --
> > Ricardo Ribalda <ribalda@...omium.org>
> >



-- 
Ricardo Ribalda