Re: [PATCH 3/3] snd/hda: Protect concurrent display_power_status with a mutex

[Takashi Iwai <tiwai@suse.de>]

On Mon, 14 Jan 2019 21:57:15 +0100,
Chris Wilson wrote:
> 
> Quoting Takashi Iwai (2019-01-14 18:00:02)
> > On Mon, 14 Jan 2019 18:51:31 +0100,
> > Chris Wilson wrote:
> > > 
> > > Quoting Takashi Iwai (2019-01-14 17:46:57)
> > > > On Mon, 14 Jan 2019 18:37:53 +0100,
> > > > Chris Wilson wrote:
> > > > > 
> > > > > Just in case the audio linkage is swapped between components during the
> > > > > runtime pm sequence, we need to protect the rpm tracking with a mutex.
> > > > 
> > > > It's not clear to me how does this happens.
> > > > Could you elaborate a bit more the scenario?
> > > 
> > > The code is written such that multiple bits within display_power_status
> > > can be set and cleared simultaneously. There was no serialisation
> > > mentioned in the routine, so I was fearful that the display_power_active
> > > here was being accessed concurrently -- and if that was explaining why
> > > snd/hda appears to be leaking the runtime pm (or at least is holding on
> > > to the wakeref longer than igt expects, > 10s).
> > 
> > Aha, and does patch actually "fix" the issue...?
> 
> Not sure yet; it's a temperamental issue in CI and my chief suspect is that
> it's just a misconfiguration of the rpm autosuspend. What may point
> towards the scenario above is if i915.ko module unloading has any impact
> on it.
>  
> > It's a simple mutex addition, so no big show, and I'm fine with it,
> > but just wonder whether it really helped.
> 
> Yeah, it just looked suspicious when reviewing the code, will throw it
> at CI a few times to see if it sticks.

OK, would you re-submit the patchset if it's confirmed to fix the
issue?  Then we should mark it Cc-to-stable as a real fix, at least.


thanks,

Takashi
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