Comment # 7 on bug 1039441 from Takashi Iwai

Looks like an issue of uvc webcam.

[12724.398292] usb 1-1.2: USB disconnect, device number 3
[12724.399781] uvcvideo: Failed to resubmit video URB (-19).
[12724.435598] ------------[ cut here ]------------
[12724.435611] WARNING: CPU: 0 PID: 3614 at ../fs/sysfs/group.c:237
device_del+0x129/0x330
[12724.435613] sysfs group 'power' not found for kobject 'event9'
....
[12724.435725] CPU: 0 PID: 3614 Comm: AudioThread Not tainted 4.11.0-2-default
#1
[12724.435728] Hardware name: Hewlett-Packard HP ProBook 450 G1 Notebook
PC/1949, BIOS L76 Ver. 00.43 01/10/2013
[12724.435730] Call Trace:
[12724.435751]  dump_stack+0x5c/0x7a
[12724.435759]  __warn+0xbe/0xe0
[12724.435766]  warn_slowpath_fmt+0x4b/0x60
[12724.435772]  ? kernfs_find_and_get_ns+0x43/0x50
[12724.435775]  device_del+0x129/0x330
[12724.435782]  evdev_disconnect+0x1e/0x50
[12724.435789]  __input_unregister_device+0xad/0x170
[12724.435795]  input_unregister_device+0x41/0x70
[12724.435804]  uvc_delete+0x15/0x120 [uvcvideo]
[12724.435823]  device_release+0x2d/0x90
[12724.435828]  kobject_release+0x65/0x180
[12724.435840]  v4l2_release+0x42/0x70 [videodev]
[12724.435847]  __fput+0xc7/0x1d0
[12724.435853]  task_work_run+0x79/0xa0
[12724.435859]  exit_to_usermode_loop+0xa4/0xb0
[12724.435865]  syscall_return_slowpath+0x54/0x60
[12724.435872]  entry_SYSCALL_64_fastpath+0xab/0xad
[12724.435876] ---[ end trace 0604e6fed1b81f89 ]---
[12724.459584] ------------[ cut here ]------------

So it spews multiple warnings due to the sysfs removal.  The recent kernel
removes sysfs entries recursively, but the driver seems still trying to remove
the individual entries that have been already removed.

If my guess is correct, it should be merely harmless warnings.