[PATCH RESEND] drm: fix crash in drm_minor_alloc_release

[Stanislaw Gruszka]

On Mon, Nov 07, 2022 at 05:56:36PM +0200, Ville Syrjälä wrote:
> On Mon, Nov 07, 2022 at 04:40:41PM +0100, Stanislaw Gruszka wrote:
> > On Mon, Nov 07, 2022 at 05:10:48PM +0200, Ville Syrjälä wrote:
> > > On Mon, Nov 07, 2022 at 03:45:00PM +0100, Stanislaw Gruszka wrote:
> > > > index 8214a0b1ab7f..e3a1243dd2ae 100644
> > > > --- a/drivers/gpu/drm/drm_drv.c
> > > > +++ b/drivers/gpu/drm/drm_drv.c
> > > > @@ -102,7 +102,8 @@ static void drm_minor_alloc_release(struct drm_device *dev, void *data)
> > > >  
> > > >  	WARN_ON(dev != minor->dev);
> > > >  
> > > > -	put_device(minor->kdev);
> > > > +	if (!IS_ERR(minor->kdev))
> > > > +		put_device(minor->kdev);
> > > 
> > > Assigning error pointers into things is a terrible idea.
> > > IMO the correct fix would be to not return some
> > > half-constructed garbage from drm_minor_alloc().
> > > So basically should at least partically revert
> > > commit f96306f9892b ("drm: manage drm_minor cleanup with drmm_")
> > 
> > I would prefer to not change any ordering or remove drmm_* stuff, since
> > as pointed to above commit message, things are tricky there.
> 
> Looks to me that it's only tricky because of drmm. Without that it was
> totally clear what was happening. I think if the managed stuff is making
> stuff more tricky then it has failed its purpose.

I'm not huge fan of managed resources everywhere either, but I think
we should do rather small fixes for bugs to avoid regressions.

> > I think assigning NULL to minor->kdev should be fine:
> > 
> > 	if (IS_ERR(minor->kdev)) {
> > 		r = PTR_ERR(minor->kdev);
> > 		minor->kdev = NULL;
> > 		return r;
> > 	}

Seems having minor->kdev NULL was ordinal Daniel idea in commit
f96306f9892b, but was not done properly when finally patch get's in.

Regards
Stanislaw