[PATCH] drm: modify drm_global_item_ref to avoid two times of writing ref->object

[Huang Rui]

On Tue, Sep 06, 2016 at 10:33:18PM +0800, Sean Paul wrote:
> On Mon, Sep 5, 2016 at 3:00 AM, Huang Rui <ray.huang at amd.com> wrote:
> > In previous drm_global_item_ref, there are two times of writing
> > ref->object if item->refcount is 0. So this patch does a minor update
> > to put alloc and init ref firstly, and then to modify the item of glob
> > array. Use "else" to avoid two times of writing ref->object. It can
> > make the code logic more clearly.
> >
> > Signed-off-by: Huang Rui <ray.huang at amd.com>
> > ---
> >  drivers/gpu/drm/drm_global.c | 14 +++++++-------
> >  1 file changed, 7 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_global.c b/drivers/gpu/drm/drm_global.c
> > index 3d2e91c..3abe738 100644
> > --- a/drivers/gpu/drm/drm_global.c
> > +++ b/drivers/gpu/drm/drm_global.c
> > @@ -70,25 +70,25 @@ int drm_global_item_ref(struct drm_global_reference *ref)
> >
> >         mutex_lock(&item->mutex);
> >         if (item->refcount == 0) {
> > -               item->object = kzalloc(ref->size, GFP_KERNEL);
> > -               if (unlikely(item->object == NULL)) {
> > +               ref->object = kzalloc(ref->size, GFP_KERNEL);
> > +               if (unlikely(ref->object == NULL)) {
> >                         ret = -ENOMEM;
> >                         goto out_err;
> >                 }
> > -
> > -               ref->object = item->object;
> >                 ret = ref->init(ref);
> >                 if (unlikely(ret != 0))
> >                         goto out_err;
> >
> > -       }
> > +               item->object = ref->object;
> > +       } else
> > +               ref->object = item->object;
> > +
> 
> You should add the braces to all blocks if they're present in any block.
> 
> >         ++item->refcount;
> > -       ref->object = item->object;
> >         mutex_unlock(&item->mutex);
> >         return 0;
> >  out_err:
> >         mutex_unlock(&item->mutex);
> > -       item->object = NULL;
> > +       ref->object = NULL;
> 
> It seems like you're leaking memory here. Do you need a
> kfree(ref->object) before this?

Yep, right. The original code seems to missed a kfree exceptional handle.

> 
> I think perhaps you can simplify (or maybe streamline is a better
> word) things better by unifying the unlock and return. Something like:
> 

Thanks, will update it in V2.

Rui