[ Upstream commit 10e1fdb958 ]
Currently, disconnecting a USB webcam while it is in use prints out a
number of warnings, such as:
WARNING: CPU: 2 PID: 3118 at /build/linux-ezBi1T/linux-4.8.0/fs/sysfs/group.c:237 sysfs_remove_group+0x8b/0x90
sysfs group ffffffffa7cd0780 not found for kobject 'event13'
This has been noticed before. [0]
This is because of the order in which things are torn down.
If there are no streams active during a USB disconnect:
- uvc_disconnect() is invoked via device_del() through the bus
notifier mechanism.
- this calls uvc_unregister_video().
- uvc_unregister_video() unregisters the video device for each
stream,
- because there are no streams open, it calls uvc_delete()
- uvc_delete() calls uvc_status_cleanup(), which cleans up the status
input device.
- uvc_delete() calls media_device_unregister(), which cleans up the
media device
- uvc_delete(), uvc_unregister_video() and uvc_disconnect() all
return, and we end up back in device_del().
- device_del() then cleans up the sysfs folder for the camera with
dpm_sysfs_remove(). Because uvc_status_cleanup() and
media_device_unregister() have already been called, this all works
nicely.
If, on the other hand, there *are* streams active during a USB disconnect:
- uvc_disconnect() is invoked
- this calls uvc_unregister_video()
- uvc_unregister_video() unregisters the video device for each
stream,
- uvc_unregister_video() and uvc_disconnect() return, and we end up
back in device_del().
- device_del() then cleans up the sysfs folder for the camera with
dpm_sysfs_remove(). Because the status input device and the media
device are children of the USB device, this also deletes their
sysfs folders.
- Sometime later, the final stream is closed, invoking uvc_release().
- uvc_release() calls uvc_delete()
- uvc_delete() calls uvc_status_cleanup(), which cleans up the status
input device. Because the sysfs directory has already been removed,
this causes a WARNing.
- uvc_delete() calls media_device_unregister(), which cleans up the
media device. Because the sysfs directory has already been removed,
this causes another WARNing.
To fix this, we need to make sure the devices are always unregistered
before the end of uvc_disconnect(). To this, move the unregistration
into the disconnect path:
- split uvc_status_cleanup() into two parts, one on disconnect that
unregisters and one on delete that frees.
- move v4l2_device_unregister() and media_device_unregister() into
the disconnect path.
[0]: https://lkml.org/lkml/2016/12/8/657
[Renamed uvc_input_cleanup() to uvc_input_unregister()]
Signed-off-by: Daniel Axtens <dja@axtens.net>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
13e976069e