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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200820101502.GB6593@pendragon.ideasonboard.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/20/20 3:15 AM, Laurent Pinchart wrote: [ ... ] >> usb_set_interface() should not be called anymore after uvc_disconnect(), >> or at east I think so (is that documented anywhere ?). >> Yet, that obviously happens, and it happens completely outside lock >> control. And this is just one instance where I was actually able >> to see the problem. I am quite sure that there are more. > > Let's hope there are not too many :-) As you can see from the stack > trace, this happens at .release() (a.k.a. last close()) time. This code > path is the only one that the V4L2 core can't protect fully for drivers. > The good news is that there's thus only one code path that drivers would > need to handle manually. > > I think we could fix this one by calling uvc_queue_release() in > uvc_disconnect(), after unregistering the video devices. The > uvc_queue_release() call in the .release() path would then become a > no-op, as everything will be stopped already. > I'll give that a try. I plan to add some instrumentation into the code to check if there are any other usb calls after uvc_disconnect(). We'll see if that was the only one, or if I can catch more. Thanks, Guenter