linux-kernel - Re: [PATCH v7 2/2] ASoC: SOF: Fix deadlock when shutdown a frozen userspace

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Date:   Thu, 1 Dec 2022 11:03:46 +0200 (EET)
From:   Kai Vehmanen <kai.vehmanen@...ux.intel.com>
To:     Ricardo Ribalda <ribalda@...omium.org>
cc:     Steven Rostedt <rostedt@...dmis.org>,
        Peter Ujfalusi <peter.ujfalusi@...ux.intel.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Chromeos Kdump <chromeos-kdump@...gle.com>,
        Mark Brown <broonie@...nel.org>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Daniel Baluta <daniel.baluta@....com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Takashi Iwai <tiwai@...e.com>,
        Alsa-devel <alsa-devel@...a-project.org>,
        sound-open-firmware@...a-project.org, kexec@...ts.infradead.org,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 2/2] ASoC: SOF: Fix deadlock when shutdown a frozen
 userspace

Hi,

On Wed, 30 Nov 2022, Ricardo Ribalda wrote:

> During kexec(), the userspace might frozen. Therefore we cannot wait
> for it to complete.
[...]
> --- a/sound/soc/sof/core.c
> +++ b/sound/soc/sof/core.c
> @@ -9,6 +9,7 @@
>  //
>  
>  #include <linux/firmware.h>
> +#include <linux/kexec.h>
>  #include <linux/module.h>
>  #include <sound/soc.h>
>  #include <sound/sof.h>
> @@ -484,7 +485,8 @@ int snd_sof_device_shutdown(struct device *dev)
>  	 * make sure clients and machine driver(s) are unregistered to force
>  	 * all userspace devices to be closed prior to the DSP shutdown sequence
>  	 */
> -	sof_unregister_clients(sdev);
> +	if (!kexec_with_frozen_processes())
> +		sof_unregister_clients(sdev);
>  
>  	snd_sof_machine_unregister(sdev, pdata);

I think the case you hit was specifically snd_card_disconnect_sync() that 
gets called via snd_sof_machine_unregister(), right, so you'd have to skip 
both sof_unregister_clients() and the machine_unregister().

Skipping ok might be an ok solution here. There's clearly a problem and we 
cannot just drop these calls in the general case (when we are going to 
S5), but in the specific case of kexec, this is probably safe. And I agree 
one way or another this needs to be fixed. Pierre and others what do you 
think?

Br, Kai