amd64/156726: snd_uaudio(4) fails to detach when mixer is open

[Arnaud Lacombe]

>Number:         156726
>Category:       amd64
>Synopsis:       snd_uaudio(4) fails to detach when mixer is open
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-amd64
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Apr 29 20:30:12 UTC 2011
>Closed-Date:
>Last-Modified:
>Originator:     Arnaud Lacombe
>Release:        8.2-STABLE
>Organization:
n/a
>Environment:
FreeBSD shai 8.2-STABLE FreeBSD 8.2-STABLE #1: Wed Mar  9 15:22:10 EST 2011
>Description:
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
open aumix(1)
unplug the adapter

>Fix:


>Release-Note:
>Audit-Trail:
>Unformatted: