Re: [Intel-gfx] [PATCH v2] ALSA: hda/i915 - avoid hung task timeout in i915 wait

[Takashi Iwai <tiwai@suse.de>]

On Wed, 09 Mar 2022 10:02:13 +0100,
Tvrtko Ursulin wrote:
> 
> 
> On 09/03/2022 08:39, Kai Vehmanen wrote:
> > Hi,
> >
> > On Wed, 9 Mar 2022, Tvrtko Ursulin wrote:
> >
> >>> -			/* 60s timeout */
> >>
> >> Where does this 60s come from and why is the fix to work around
> >> DEFAULT_HUNG_TASK_TIMEOUT in a hacky way deemed okay? For instance would
> >> limiting the wait here to whatever the kconfig is set to be an option?
> >
> > this was discussed in
> > https://lists.freedesktop.org/archives/intel-gfx/2022-February/290821.html
> > ... and that thread concluded it's cleaner to split the wait than try
> > to figure out hung-task configuration from middle of audio driver.
> >
> > The 60sec timeout comes from 2019 patch "ALSA: hda: Extend i915 component
> > bind timeout" to fix an issue reported by Paul Menzel (cc'ed).
> >
> > This patch keeps the timeout intact.
> 
> I did not spot discussion touching on the point I raised.
> 
> How about not fight the hung task detector but mark your wait context
> as "I really know what I'm doing - not stuck trust me".

The question is how often this problem hits.  Basically it's a very
corner case, and I even think we may leave as is; that's a matter of
configuration, and lowering such a bar should expect some
side-effect. OTOH, if the problem happens in many cases, it's
beneficial to fix in the core part, indeed.

> Maybe using
> wait_for_completion_killable_timeout would do it since
> snd_hdac_i915_init is allowed to fail with an error already?

It makes it killable -- which is a complete behavior change.


Takashi