On Tue, 01 Mar 2022 05:16:38 +0100, Shengjiu 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://github.com/tiwai/alsa-lib

??

thanks,

Takashi