Re: [PATCH v4] ALSA: core: Fix deadlock when shutdown a frozen userspace

[Pierre-Louis Bossart]

On 11/28/22 07:42, Ricardo Ribalda wrote:
> During kexec(), the userspace is frozen. Therefore we cannot wait for it
> to complete.
> 
> Avoid running snd_sof_machine_unregister during shutdown.
> 
> This fixes:
> 
> [   84.943749] Freezing user space processes ... (elapsed 0.111 seconds) done.
> [  246.784446] INFO: task kexec-lite:5123 blocked for more than 122 seconds.
> [  246.819035] Call Trace:
> [  246.821782]  <TASK>
> [  246.824186]  __schedule+0x5f9/0x1263
> [  246.828231]  schedule+0x87/0xc5
> [  246.831779]  snd_card_disconnect_sync+0xb5/0x127
> ...
> [  246.889249]  snd_sof_device_shutdown+0xb4/0x150
> [  246.899317]  pci_device_shutdown+0x37/0x61
> [  246.903990]  device_shutdown+0x14c/0x1d6
> [  246.908391]  kernel_kexec+0x45/0xb9
> 
> And:
> 
> [  246.893222] INFO: task kexec-lite:4891 blocked for more than 122 seconds.
> [  246.927709] Call Trace:
> [  246.930461]  <TASK>
> [  246.932819]  __schedule+0x5f9/0x1263
> [  246.936855]  ? fsnotify_grab_connector+0x5c/0x70
> [  246.942045]  schedule+0x87/0xc5
> [  246.945567]  schedule_timeout+0x49/0xf3
> [  246.949877]  wait_for_completion+0x86/0xe8
> [  246.954463]  snd_card_free+0x68/0x89
> ...
> [  247.001080]  platform_device_unregister+0x12/0x35
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 83bfc7e793b5 ("ASoC: SOF: core: unregister clients and machine drivers in .shutdown")
> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> ---
> To: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
> To: Liam Girdwood <lgirdwood@xxxxxxxxx>
> To: Peter Ujfalusi <peter.ujfalusi@xxxxxxxxxxxxxxx>
> To: Bard Liao <yung-chuan.liao@xxxxxxxxxxxxxxx>
> To: Ranjani Sridharan <ranjani.sridharan@xxxxxxxxxxxxxxx>
> To: Kai Vehmanen <kai.vehmanen@xxxxxxxxxxxxxxx>
> To: Daniel Baluta <daniel.baluta@xxxxxxx>
> To: Mark Brown <broonie@xxxxxxxxxx>
> To: Jaroslav Kysela <perex@xxxxxxxx>
> To: Takashi Iwai <tiwai@xxxxxxxx>
> Cc: sound-open-firmware@xxxxxxxxxxxxxxxx
> Cc: alsa-devel@xxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
> Changes in v4:
> - Do not call snd_sof_machine_unregister from shutdown.
> - Link to v3: https://lore.kernel.org/r/20221127-snd-freeze-v3-0-a2eda731ca14@xxxxxxxxxxxx
> 
> Changes in v3:
> - Wrap pm_freezing in a function
> - Link to v2: https://lore.kernel.org/r/20221127-snd-freeze-v2-0-d8a425ea9663@xxxxxxxxxxxx
> 
> Changes in v2:
> - Only use pm_freezing if CONFIG_FREEZER 
> - Link to v1: https://lore.kernel.org/r/20221127-snd-freeze-v1-0-57461a366ec2@xxxxxxxxxxxx
> ---
>  sound/soc/sof/core.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/sound/soc/sof/core.c b/sound/soc/sof/core.c
> index 3e6141d03770..9616ba607ded 100644
> --- a/sound/soc/sof/core.c
> +++ b/sound/soc/sof/core.c
> @@ -475,19 +475,16 @@ EXPORT_SYMBOL(snd_sof_device_remove);
>  int snd_sof_device_shutdown(struct device *dev)
>  {
>  	struct snd_sof_dev *sdev = dev_get_drvdata(dev);
> -	struct snd_sof_pdata *pdata = sdev->pdata;
>  
>  	if (IS_ENABLED(CONFIG_SND_SOC_SOF_PROBE_WORK_QUEUE))
>  		cancel_work_sync(&sdev->probe_work);
>  
>  	/*
> -	 * make sure clients and machine driver(s) are unregistered to force
> -	 * all userspace devices to be closed prior to the DSP shutdown sequence
> +	 * make sure clients are unregistered prior to the DSP shutdown
> +	 * sequence.
>  	 */
>  	sof_unregister_clients(sdev);
>  
> -	snd_sof_machine_unregister(sdev, pdata);
> -

The comment clearly says that we do want all userspace devices to be
closed. This was added in 83bfc7e793b5 ("ASoC: SOF: core: unregister
clients and machine drivers in .shutdown") precisely to avoid a platform
hang if the devices are used after the shutdown completes.

So you are not fixing 83bfc7e793b5, just re-adding a problem to fix
another one...