[PATCH 1/2] drm/udl: fix a NULL pointer reference in udl_gem_free_object().

[Haixia Shi]

For details see https://bugs.chromium.org/p/chromium/issues/detail?id=468050

So drm_mode_config_cleanup() is called from udl_driver_unload() in
which we found there's still a framebuffer left, hence the WARN in
drm_crtc.c:5495. This also forcefully releases all the buffers.

A bit later the actual drm_buf_release comes in which attempts to
release the buffer again.

On Wed, Aug 31, 2016 at 12:55 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
>
> On Tue, Aug 30, 2016 at 02:50:20PM -0700, Haixia Shi wrote:
> > Previously this function had a NULL pointer check for gem->map_list.map, but
> > that line was refactored after commit 0de23977cfeb5b357ec884ba15417ae118ff9e9bb
> > ("drm/gem: convert to new unified vma manager").
> >
> > After the refactor it is still necessasry to check that the vma manager is not
> > NULL because udl_gem_free_object() may come in after the vma manager is destroyed.
>
> When/how does this happen? Backtrace? Destroying the vma manager before
> the objects are all gone sounds a bit fishy.
> -Daniel
>
> >
> > Signed-off-by: Haixia Shi <hshi at chromium.org>
> > Reviewed-by: Stéphane Marchesin <marcheu at chromium.org>
> > ---
> >  drivers/gpu/drm/udl/udl_gem.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/udl/udl_gem.c b/drivers/gpu/drm/udl/udl_gem.c
> > index 818e707..72e1bd4 100644
> > --- a/drivers/gpu/drm/udl/udl_gem.c
> > +++ b/drivers/gpu/drm/udl/udl_gem.c
> > @@ -204,7 +204,8 @@ void udl_gem_free_object(struct drm_gem_object *gem_obj)
> >       if (obj->pages)
> >               udl_gem_put_pages(obj);
> >
> > -     drm_gem_free_mmap_offset(gem_obj);
> > +     if (gem_obj->dev->vma_offset_manager)
> > +             drm_gem_free_mmap_offset(gem_obj);
> >  }
> >
> >  /* the dumb interface doesn't work with the GEM straight MMAP
> > --
> > 2.8.0.rc3.226.g39d4020
> >
> > _______________________________________________
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> > dri-devel at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch