https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=202275
Bug ID: 202275
Summary: USB SX lock hang involving sound devices
Product: Base System
Version: 10.2-BETA1
Hardware: amd64
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: kern
Assignee: freebsd-bugs@FreeBSD.org
Reporter: cgull+l-freebsd-bugzi...@glup.org
FreeBSD 10.2-RC2
I think something in the USB or audio stack has a USB locking issue. I think
this duplicates Bug 194727.
I had a strange USB hang this afternoon. I took a little nap, and my display
went to sleep (this is important, see below). On waking and returning to my
computer, my two USB mice were hung, but a USB keyboard and a Bluetooth
keyboard connected via a USB host controller continued to work.
Investigation found this appearing in /var/log/messages every 2-3 seconds:
Aug 12 15:38:54 lister kernel: pcm6: unregister: mixer busy
Aug 12 15:38:54 lister kernel: pcm6: Waiting for sound application to exit!
I ran 'usbconfig -l', it hung. ^T revealed it was waiting on [USB config SX
lock].
I finally discovered a couple of instances of kdeinit4 that had /dev/mixer6
open. Killing them caused the messages to stop, the USB stack to recover, and
my mice started working again.
I have a Dell P2815Q monitor with USB3 hub attached to my system. Plugged into
that is an old Microsoft USB webcam. This webcam's uaudio0 device was attached
to pcm6. The monitor is set to an energy save mode where it powers down the
hub when it goes to sleep, and my system log shows the hub and webcam
disconnecting and reconnecting frequently. It also has some firmware issues
that sometimes require you to do a hard power cycle by holding the power button
down for 4s, I don't remember if I had to do that this time.
I do not know what is going on exactly, but this all suggests that something
may be inappropriately holding that USB lock while waiting for a process during
device teardown and causing other non-sound-related devices to hang.
Fortunately, my keyboards continued to work in this case.
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