Re: [PATCH v2 2/3] drm: Add a drm_gem_objects_lookup helper

[Rob Herring <robh@kernel.org>]

On Mon, Apr 1, 2019 at 10:43 AM Eric Anholt <eric@anholt.net> wrote:
>
> Chris Wilson <chris@chris-wilson.co.uk> writes:
>
> > Quoting Daniel Vetter (2019-04-01 14:06:48)
> >> On Mon, Apr 1, 2019 at 9:47 AM Rob Herring <robh@kernel.org> wrote:
> >> > +{
> >> > +       int i, ret = 0;
> >> > +       struct drm_gem_object *obj;
> >> > +
> >> > +       spin_lock(&filp->table_lock);
> >> > +
> >> > +       for (i = 0; i < count; i++) {
> >> > +               /* Check if we currently have a reference on the object */
> >> > +               obj = idr_find(&filp->object_idr, handle[i]);
> >> > +               if (!obj) {
> >> > +                       ret = -ENOENT;
> >
> > Unwind previous drm_gem_object_get(), the caller has no idea how many
> > were processed before the error.
>
> I had the same thought, but the pattern we have is that you're loading
> into a refcounted struct that will free the BOs when you're done,
> anyway.

The real bug here is if allocation of the array fails. The BO array
may be NULL when the count is not. So this V3D cleanup hunk:

for (i = 0; i < exec->bo_count; i++)
  drm_gem_object_put_unlocked(&exec->bo[i]->base.base);
  kvfree(exec->bo);

Needs to be wrapped with 'if (exec->bo)'. We have a similar problem
with fence arrays too.

Thanks to Steven for noticing this copied code in panfrost.

Rob