Re: Issue in pcm_dsnoop.c in alsa-lib

[Takashi Iwai <tiwai@suse.de>]

On Fri, 04 Mar 2022 09:35:28 +0100,
S.J. Wang wrote:
> 
> 
> 
> > >
> > > Hi Takashi Iwai, Jaroslav Kysela
> > >
> > >     We encountered an issue in the pcm_dsnoop use case, could you
> > > please help to have a look?
> > >
> > >     *Issue description:*
> > >     With two instances for dsnoop type device running in parallel,
> > > after suspend/resume,  one of the instances will be hung in memcpy
> > > because the very large copy size is obtained.
> > >
> > > #3 0x0000ffffa78d5098 in snd_pcm_dsnoop_sync_ptr
> > (pcm=0xaaab06563da0)
> > > at pcm_dsnoop.c:158 dsnoop = 0xaaab06563c20 slave_hw_ptr = 64
> > > old_slave_hw_ptr = 533120 avail = *187651522444320*
> > >
> > >   * Reason analysis: *
> > >    The root cause that I analysis is that after suspend/resume,  one
> > > instance will get the SND_PCM_STATE_SUSPENDED state from slave pcm
> > device,
> > >   then it will do snd_pcm_prepare() and snd_pcm_start(),  which will
> > > reset the dsnoop->slave_hw_ptr and the hw_ptr of slave pcm device,
> > > then the state of this instance is correct.  But another instance may
> > > not get the SND_PCM_STATE_SUSPENDED state from slave pcm device
> > > because slave device may have been recovered by first instance,  so
> > > the dsnoop->slave_hw_ptr is not reset.  but because hw_ptr of slave
> > > pcm device has been reset,  so there will be a very large "avail" size.
> > >
> > >    *Solution:*
> > >    I didn't come up with a fix for this issue,  seems there is no easy
> > > way to let another instance know this case and reset the
> > > dsnoop->slave_hw_ptr,  could you please help?
> > 
> > Could you try topic/pcm-direct-resume branch on
> > 
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub
> > .com%2Ftiwai%2Falsa-
> > lib&data=04%7C01%7Cshengjiu.wang%40nxp.com%7C95f97de3f2c840d
> > 9853508d9fd2e79ea%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C
> > 637819198319430045%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM
> > DAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdat
> > a=WWX1ZlcQhJF3pHJdHPIH%2B0xG9o%2FjQnHG5fHDbKXwQwE%3D&r
> > eserved=0
> > 
> 
> Thanks,  I push my test result in https://github.com/alsa-project/alsa-lib/issues/213
> Could you please review?

Please keep the discussion on ML.


Takashi