[RFC PATCH v2 0/5] ASoC: soc-pcm: fix trigger race conditions with shared BE

[Pierre-Louis Bossart]

>> I think the only solution is to follow the example of the PCM case,
>> where the type of lock depends on the FE types, with the assumption that
>> there are no mixed atomic/non-atomic FE configurations.
> 
> Yes, and I guess we can simply replace those all card->dpcm_lock with
> FE's stream lock.  It'll solve the atomicity problem, too, and the FE
> stream lock can be applied outside the loop of dpcm_be_disconnect()
> gracefully.
> 
> And, this should solve the race with dpcm_be_dai_trigger() as well,
> because it's called from dpcm_fe_dai_trigger() that is called already
> inside the FE's stream lock held by PCM core.  A PoC is something like
> below.  (I replaced the superfluous *_irqsave with *_irq there)

No I don't think so. The code starts from an FE and loops for all the
BEs connected to that FE, but we want to serialize at the BE level! we
really need a dpcm lock at the card level, not the FE/stream level.

I am testing a quick set of changes at
https://github.com/thesofproject/linux/pull/3201,  where I also replaced
irqsave by irq btw.