On Fri, Dec 09, 2016 at 01:09:21AM +0200, Laurent Pinchart wrote: > Hi Dave, > > (CC'ing LKML and Greg KH) > > On Thursday 08 Dec 2016 12:31:55 Dave Stevenson wrote: > > Hi All. > > > > I'm working with a USB webcam which has been seen to spontaneously > > disconnect when in use. That's a separate issue, but when it does it > > throws a load of warnings into the kernel log if there is a file handle > > on the device open at the time, even if not streaming. > > > > I've reproduced this with a generic Logitech C270 webcam on: > > - Ubuntu 16.04 (kernel 4.4.0-51) vanilla, and with the latest media tree > > from linuxtv.org > > - Ubuntu 14.04 (kernel 4.4.0-42) vanilla > > - an old 3.10.x tree on an embedded device. > > > > To reproduce: > > - connect USB webcam. > > - run a simple app that opens /dev/videoX, sleeps for a while, and then > > closes the handle. > > - disconnect the webcam whilst the app is running. > > - read kernel logs - observe warnings. We get the disconnect logged as > > it occurs, but the warnings all occur when the file descriptor is > > closed. (A copy of the logs from my Ubuntu 14.04 machine are below). > > > > I can fully appreciate that the open file descriptor is holding > > references to a now invalid device, but is there a way to avoid them? Or > > do we really not care and have to put up with the log noise when doing > > such silly things? > > This is a known problem, caused by the driver core trying to remove the same > sysfs attributes group twice. Ick, not good. > The group is first removed when the USB device is disconnected. The input > device and media device created by the uvcvideo driver are children of the USB > interface device, which is deleted from the system when the camera is > unplugged. Due to the parent-child relationship, all sysfs attribute groups of > the children are removed. Wait, why is the USB device being removed from sysfs at this point, didn't the input and media subsystems grab a reference to it so that it does not disappear just yet? > Then, when the device node is closed, the media device and input device are > unregistered, causing the corresponding devices to be deleted too. The driver > core tries to remove the sysfs attributes groups related to those devices, and > issues a warning as they have been removed already. > > I'm not sure how to fix that, any hint from LKML would be appreciated. Properly grab a reference to the USB device? :) If that's already happening, please let me know and I'll see what needs to be done, but I think that should solve the issue for you. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
