On Fri, Dec 09, 2016 at 11:14:41AM +0200, Laurent Pinchart wrote: > Hi Greg, > > On Friday 09 Dec 2016 10:11:13 Greg KH wrote: > > On Fri, Dec 09, 2016 at 10:59:24AM +0200, Laurent Pinchart wrote: > > > On Friday 09 Dec 2016 08:25:52 Greg KH wrote: > > >> On Fri, Dec 09, 2016 at 01:09:21AM +0200, Laurent Pinchart wrote: > > >>> 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? > > > > > > References are taken in uvc_prove(): > > > dev->udev = usb_get_dev(udev); > > > dev->intf = usb_get_intf(intf); > > > > s/uvc_prove/uvc_probe/ ? :) > > Oops :-) > > > > and released in uvc_delete(), called when the last video device node is > > > closed. This prevents the device from being released (freed), but > > > device_del() is synchronous to device unplug as far as I understand. > > > > Ok, good, that means the UVC driver is doing the right thing here. > > > > But the sysfs files should only be attempted to be removed by the driver > > core once, when the device is removed from sysfs, not twice, which is > > really odd. > > > > Is there a copy of the "simple app that grabs the device node" anywhere > > so that I can test it out here with my USB camera device to try to track > > down where the problem is? > > Sure. The easiest way is to grab http://git.ideasonboard.org/yavta.git and run > > yavta -c /dev/video0 > > (your mileage may vary if you have other video devices) I'll point it at the correct device, /dev/video0 is built into this laptop and can't be physically removed :) > While the application is running, unplug the webcam, and then terminate the > application with ctrl-C. Ok, will try this out this afternoon and let you know how it goes. 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
