When a userland application has an open file descriptor to /dev/pcmN,
backed by an snd_uaudio(4) based device, trying to detach this device
will hang the USB stack until the userland application is closed.
Ultimately, this could lead to a complete stall of the USB stack.
It would be expected that every child of snd_uaudio(4) just detach
themselves, letting the userland die with EIO.
How-To-Repeat: plug a snd_uaudio adapter
unplug the adapter
This sounds potentially like a USB stack issue to me.
On Thursday 16 August 2012 14:54:00 firstname.lastname@example.org wrote:
> Synopsis: [snd_uaudio]: snd_uaudio(4) fails to detach when mixer is open
> Responsible-Changed-From-To: freebsd-multimedia->freebsd-usb
> Responsible-Changed-By: gavin
> Responsible-Changed-When: Thu Aug 16 12:53:15 UTC 2012
> This sounds potentially like a USB stack issue to me.
This is not a USB stack problem, but a sound system issue.
This is a known issue.
I ran into this problem in 13.0-RELEASE. In my case, suspend (via acpiconf) hangs on uaudio_detach_sub() ("Waiting for sound application to exit!") because an application is holding the mixer open. Can we re-open this issue for investigating a fix on the sound side, or should I open a new PR?
(In reply to Kevin Zheng from comment #4)
Looks like this duplicates 194727. Could someone with permissions please add this to the duplicates list?