alsa-project/alsa-lib issue #213 was opened from TE-N-ShengjiuWang:
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?
Issue URL : https://github.com/alsa-project/alsa-lib/issues/213
Repository URL: https://github.com/alsa-project/alsa-lib
