amd64/156725: USB stack stall cause complete system input loss

[Arnaud Lacombe]

The following reply was made to PR amd64/156725; it has been noted by GNATS.

From: Arnaud Lacombe <lacombar at gmail.com>
To: bug-followup at FreeBSD.org, lacombar at gmail.com
Cc:  
Subject: Re: amd64/156725: USB stack stall cause complete system input loss
Date: Fri, 29 Apr 2011 16:48:52 -0400

 this bug is tightly related to amd64/156726. Considering the following scenario:
 
  1) plug a snd_uaudio(4)-based device
  2) open aumix(1) on, pcmN, the mixer device attached to the
 previously attached device
  3) unplug the snd_uaudio(4)-based device
  [the USB stack busy wait pcmN detach]
  4) close aumix(1)
  [pcmN finally detach]
 
 If there is no USB activity (ie, no attach/detach, but "normal" hid
 activity), the USB stack recovers. If another USB device is
 attached/detached while the stack busy wait on pcmN detachment
 (between step 3 and step 4), events ends up being queued. Once step 4
 is done, events gets processed, however, once completed the USB stall,
 ie. no more mouse or keyboard.
 
 At this point, I do not see any USB related message while the system halts.