From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from perceval.ideasonboard.com ([95.142.166.194]:45479 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751445Ab3IIKKB (ORCPT ); Mon, 9 Sep 2013 06:10:01 -0400 From: Laurent Pinchart To: Hans Verkuil Cc: Sylwester Nawrocki , Sylwester Nawrocki , linux-media@vger.kernel.org, Kyungmin Park Subject: Re: [PATCH] V4L: Drop meaningless video_is_registered() call in v4l2_open() Date: Mon, 09 Sep 2013 12:10:05 +0200 Message-ID: <26516577.dQgL4XrfDY@avalon> In-Reply-To: <522D9DD6.2080609@xs4all.nl> References: <1375446449-27066-1-git-send-email-s.nawrocki@samsung.com> <5584569.Fq1hO5v8IF@avalon> <522D9DD6.2080609@xs4all.nl> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-media-owner@vger.kernel.org List-ID: Hi Hans, On Monday 09 September 2013 12:07:18 Hans Verkuil wrote: > On 09/09/2013 12:00 PM, Laurent Pinchart wrote: > > On Monday 09 September 2013 11:07:43 Hans Verkuil wrote: > >> On 09/06/2013 12:33 AM, Sylwester Nawrocki wrote: > > > > [snip] > > > >>> The main issue as I see it is that we need to track both driver remove() > >>> and struct device .release() calls and free resources only when last of > >>> them executes. Data structures which are referenced in fops must not be > >>> freed in remove() and we cannot use dev_get_drvdata() in fops, e.g. not > >>> protected with device_lock(). > >> > >> You can do all that by returning 0 if probe() was partially successful > >> (i.e. one or more, but not all, nodes were created successfully) by > >> doing what I described above. I don't see another way that doesn't > >> introduce a race condition. > > > > But isn't this just plain wrong ? If probing fails, I don't see how > > returning success could be a good idea. > > Well, the nodes that are created are working fine. So it's partially OK :-) > > That said, yes it would be better if it could safely clean up and return an > error. But it is better than returning an error and introducing a race > condition. > > >> That doesn't mean that there isn't one, it's just that I don't know of a > >> better way of doing this. > > > > We might need support from the device core. > > I do come back to my main question: has anyone actually experienced this > error in a realistic scenario? Other than in very low-memory situations I > cannot imagine this happening. What about running out of minors, which could very well happen with subdev nodes in complex SoCs ? > I'm not sure whether you want to spend a lot of time trying to fix this all > perfectly. That's why I am suggesting just unregistering everything and > returning 0 in probe(). Not ideal, but at least it's safe (as far as I can > tell). -- Regards, Laurent Pinchart