From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932871AbcLII7C (ORCPT ); Fri, 9 Dec 2016 03:59:02 -0500 Received: from galahad.ideasonboard.com ([185.26.127.97]:47822 "EHLO galahad.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932499AbcLII7A (ORCPT ); Fri, 9 Dec 2016 03:59:00 -0500 From: Laurent Pinchart To: Greg KH Cc: Dave Stevenson , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: uvcvideo logging kernel warnings on device disconnect Date: Fri, 09 Dec 2016 10:59:24 +0200 Message-ID: <3934137.UccFJV1Tl7@avalon> User-Agent: KMail/4.14.10 (Linux/4.8.6-gentoo; KDE/4.14.24; x86_64; ; ) In-Reply-To: <20161209072552.GA1513@kroah.com> References: <4641182.Fvs5tG4yD4@avalon> <20161209072552.GA1513@kroah.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Greg, 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); 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. > > 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. -- Regards, Laurent Pinchart