Hi Hans, On Monday 09 September 2013 12:17:34 Hans Verkuil wrote: > On 09/09/2013 12:10 PM, Laurent Pinchart wrote: > > 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 ? > > Is that really realistic? What's the worst-case SoC we have in terms of > device nodes? Frankly, if this might happen then we should allow for more > minors or make the minor allocation completely dynamic. For the 4 VSP1 instances on the R-Car H2, I need 33 video nodes and 65 (if I'm not mistaken) subdev nodes. That doesn't include the camera interface. On a side note, this seems to indicate that the subdev API should probably move to the /dev/media device node. That's something else to discuss. > If you run into this situation then you have bigger problems than a > potential race condition. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
