Re: [PATCH] V4L: Drop meaningless video_is_registered() call in v4l2_open()

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

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