From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753777AbcLIJnA (ORCPT ); Fri, 9 Dec 2016 04:43:00 -0500 Received: from out4-smtp.messagingengine.com ([66.111.4.28]:33772 "EHLO out4-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751599AbcLIJm5 (ORCPT ); Fri, 9 Dec 2016 04:42:57 -0500 X-ME-Sender: X-Sasl-enc: SiG/9O9TyQK/Us5TVmp23UiNaCY9ueH1QwVGNd26blaj 1481276576 Date: Fri, 9 Dec 2016 10:43:04 +0100 From: Greg KH To: Laurent Pinchart Cc: Dave Stevenson , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: uvcvideo logging kernel warnings on device disconnect Message-ID: <20161209094304.GB4755@kroah.com> References: <3934137.UccFJV1Tl7@avalon> <20161209091113.GB27160@kroah.com> <2080235.u14sVkzQLZ@avalon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2080235.u14sVkzQLZ@avalon> User-Agent: Mutt/1.7.2 (2016-11-26) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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