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

[Takashi Iwai <tiwai@xxxxxxx>]

On Thu, 01 Dec 2022 14:22:12 +0100,
Oliver Neukum 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.

... or fixed.

> > 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()

As I already mentioned in another thread, if the user-space action has
to be cut off, we just need to call snd_card_disconnect() instead
without sync.  A quick hack would be like below (totally untested and
might be wrong, though).

In anyway, Ricardo, please stop spinning too frequently; v8 in a few 
days is way too much, and now the recipient list became unmanageable.
Let's give people some time to review and consider a better solution
at first.


thanks,

Takashi

-- 8< --
--- a/sound/soc/sof/core.c
+++ b/sound/soc/sof/core.c
@@ -475,7 +475,7 @@ 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;
+       struct snd_soc_component *component;
 
        if (IS_ENABLED(CONFIG_SND_SOC_SOF_PROBE_WORK_QUEUE))
                cancel_work_sync(&sdev->probe_work);
@@ -484,9 +484,9 @@ 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);
-
-       snd_sof_machine_unregister(sdev, pdata);
+       component = snd_soc_lookup_component(sdev->dev, NULL);
+       if (component && component->card && component->card->snd_card)
+               snd_card_disconnect(component->card->snd_card);
 
        if (sdev->fw_state == SOF_FW_BOOT_COMPLETE)
                return snd_sof_shutdown(sdev);