From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2223E13A888; Wed, 27 Nov 2024 09:42:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732700546; cv=none; b=X4getjTfMdUkif84Ujgx4qp1HB8sA+PyUA8oous2uO71e5jM20oD7qZGzxYsP72aoSQSvwe6oxymSZS6I2G3c3D3jvgxq9miW30PxK/SC3p0OzFk0VIhgq3q8dfAw8rAu7Kz0gqpwPNw4tWJYSZRbM//3THaAVLEZ0BrxyLm4OA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732700546; c=relaxed/simple; bh=KWKEWa3UIXAu4vOfBjPfx5eH26k3SHJci83eJv2qTjM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=fBc92/rnSav9JZWDNnD/pBDhXtUhorqnLMS34Jsbf10QKa36Cw+001KHlAFFFOz5bwBO4X6260AQwCaVL2pTUozgBPUv4mTF3M8ekImlu8vKztFrVcDTfPe+/JNZgZYh3IVHoJ2Uui75vVApUsGYRBGIKWCgGv6tNLAtIExZ2HA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=XDVp8uGE; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="XDVp8uGE" Received: from pendragon.ideasonboard.com (81-175-209-231.bb.dnainternet.fi [81.175.209.231]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 69465792; Wed, 27 Nov 2024 10:42:00 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1732700520; bh=KWKEWa3UIXAu4vOfBjPfx5eH26k3SHJci83eJv2qTjM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=XDVp8uGE4wQ2KBiHmPVFjkiW5WbIV13n+VdsontCe4G/OJcQIni0zLsNHGvOZE7yY c12GSVsxdHGj/sMHLcUYodVZaNVkPSKli5TMDIrowic2nciWMPaBySmTYIDbi43qIp 7tHm2twL3gPlSBzXX7JRZtBP/yGWfXzmNuAd1cVQ= Date: Wed, 27 Nov 2024 11:42:12 +0200 From: Laurent Pinchart To: Ricardo Ribalda Cc: Hans de Goede , Mauro Carvalho Chehab , Guennadi Liakhovetski , Mauro Carvalho Chehab , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 1/2] media: uvcvideo: Do not set an async control owned by other fh Message-ID: <20241127094212.GF31095@pendragon.ideasonboard.com> References: <20241127-uvc-fix-async-v1-0-eb8722531b8c@chromium.org> <20241127-uvc-fix-async-v1-1-eb8722531b8c@chromium.org> <20241127091153.GA31095@pendragon.ideasonboard.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On Wed, Nov 27, 2024 at 10:25:48AM +0100, Ricardo Ribalda wrote: > On Wed, 27 Nov 2024 at 10:12, Laurent Pinchart wrote: > > On Wed, Nov 27, 2024 at 07:46:10AM +0000, Ricardo Ribalda wrote: > > > If a file handle is waiting for a response from an async control, avoid > > > that other file handle operate with it. > > > > > > Without this patch, the first file handle will never get the event > > > associated to that operation. > > > > Please explain why that is an issue (both for the commit message and for > > me, as I'm not sure what you're fixing here). > > What about something like this: > > Without this patch, the first file handle will never get the event > associated with that operation, which can lead to endless loops in > applications. Eg: > If an application A wants to change the zoom and to know when the > operation has completed: > it will open the video node, subscribe to the zoom event, change the > control and wait for zoom to finish. > If before the zoom operation finishes, another application B changes > the zoom, the first app A will loop forever. So it's related to the userspace-visible behaviour, there are no issues with this inside the kernel ? Applications should in any case implement timeouts, as UVC devices are fairly unreliable. What bothers me with this patch is that if the device doesn't generate the event, ctrl->handle will never be reset to NULL, and the control will never be settable again. I think the current behaviour is a lesser evil. > > What may be an issue is that ctrl->handle seem to be accessed from > > different contexts without proper locking :-S > > Isn't it always protected by ctrl_mutex? Not that I can tell. At least uvc_ctrl_status_event_async() isn't called with that lock held. uvc_ctrl_set() seems OK (a lockedep assert at the beginning of the function wouldn't hurt). As uvc_ctrl_status_event_async() is the URB completion handler, a spinlock would be nicer than a mutex to protect ctrl->handle. > > > Cc: stable@vger.kernel.org > > > Fixes: e5225c820c05 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives") > > > Signed-off-by: Ricardo Ribalda > > > --- > > > drivers/media/usb/uvc/uvc_ctrl.c | 4 ++++ > > > 1 file changed, 4 insertions(+) > > > > > > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c > > > index 4fe26e82e3d1..5d3a28edf7f0 100644 > > > --- a/drivers/media/usb/uvc/uvc_ctrl.c > > > +++ b/drivers/media/usb/uvc/uvc_ctrl.c > > > @@ -1950,6 +1950,10 @@ int uvc_ctrl_set(struct uvc_fh *handle, > > > if (!(ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR)) > > > return -EACCES; > > > > > > + /* Other file handle is waiting a response from this async control. */ > > > + if (ctrl->handle && ctrl->handle != handle) > > > + return -EBUSY; > > > + > > > /* Clamp out of range values. */ > > > switch (mapping->v4l2_type) { > > > case V4L2_CTRL_TYPE_INTEGER: -- Regards, Laurent Pinchart