[RFC PATCH v3 07/13] ASoC: soc-pcm: protect for_each_dpcm_be() loops

[Sameer Pujar]

On 10/13/2021 8:00 PM, Pierre-Louis Bossart wrote:
> The D in DPCM stands for 'dynamic', which means that connections
> between FE and BE can evolve.
>
> Commit a97648697790 ("ASoC: dpcm: prevent snd_soc_dpcm use after
> free") started to protect some of the for_each_dpcm_be() loops, but
> there are still many cases that were not modified.
>
> This patch adds protection for all the remaining loops, with the
> notable exception of the dpcm_be_dai_trigger(), where the lock is
> already taken at a higher level, e.g. in snd_pcm_period_elapsed().
>
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> ---
>   sound/soc/soc-pcm.c | 86 ++++++++++++++++++++-------------------------
>   1 file changed, 39 insertions(+), 47 deletions(-)

After this, once I load sound card there are warning prints and failure:

[   71.224324] WARNING: CPU: 3 PID: 574 at 
drivers/firmware/tegra/bpmp.c:362 tegra_bpmp_transfer+0x2d0/0x328
[   71.238032] ---[ end trace 88d978f78a82134f ]---
[   71.243033] WARNING: CPU: 3 PID: 574 at 
drivers/firmware/tegra/bpmp.c:362 tegra_bpmp_transfer+0x2d0/0x328
[   71.257022] ---[ end trace 88d978f78a821350 ]---
[   71.261965] tegra-audio-graph-card sound: Can't set plla rate for 
270950400, err: -22
...


This happens because, now the atomicity is propagated to BE callbacks 
where the clock settings are done in hw_param(). On Tegra, the clock 
APIs are served by BPMP and warning is seen because of below.

   int tegra_bpmp_transfer()
   {

=>      if (WARN_ON(irqs_disabled()))
             return -EPERM;

         ...

   }


This results in hw_param() failure and all tests fail at my end.