Re: [PATCH RFC] omap3isp: prevent releasing MC too early

[Greg KH <greg@kroah.com>]

On Thu, Dec 15, 2016 at 10:57:16AM -0200, Mauro Carvalho Chehab wrote:
> Em Thu, 15 Dec 2016 09:42:35 -0300
> Javier Martinez Canillas <javier@osg.samsung.com> escreveu:
> 
> > Hello Mauro,
> > 
> > On 12/15/2016 09:37 AM, Mauro Carvalho Chehab wrote:
> > 
> > [snip]
> > 
> > > 
> > > What happens is that omap3isp driver calls media_device_unregister()
> > > too early. Right now, it is called at omap3isp_video_device_release(),
> > > with happens when a driver unbind is ordered by userspace, and not after
> > > the last usage of all /dev/video?? devices.
> > > 
> > > There are two possible fixes:
> > > 
> > > 1) at omap3isp_video_device_release(), streamoff all streams and mark
> > > that the media device will be gone.
> 
> I actually meant to say: isp_unregister_entities() here.
> 
> > > 
> > > 2) instead of using video_device_release_empty for the video->video.release,
> > > create a omap3isp_video_device_release() that will call
> > > media_device_unregister() when destroying the last /dev/video?? devnode.
> > >  
> > 
> > There's also option (3), to have a proper refcounting to make sure that
> > the media device node is not freed until all references to it are gone.
> 
> Yes, that's another alternative.
> 
> > I understand that's what Sakari's RFC patches do. I'll try to make some
> > time tomorrow to test and review his patches.
> 
> The biggest problem with Sakari's patches is that it starts by 
> reverting 3 patches, and this will cause regressions on existing
> devices.
> 
> Development should be incremental.

How can reverting patches cause regressions?  If a patch that is applied
breaks something else, it needs to be reverted, end of story.  If that
patch happened to have fixed a different issue, that's fine, we are back
to the original issue, it's not a "regression" at all, the patch was
wrong in the first place.

So please, just revert them now.  That's the correct thing to do, as we
will be back to the previous release's behavior.

thanks,

greg k-h