Re: [Intel-gfx] [PATCH v2 1/3] drm/mm: Ensure that the entry is not NULL before extracting rb_node

["Kasireddy, Vivek" <vivek.kasireddy@intel.com>]

Hi Tvrtko,

> 
> On 17/02/2022 07:50, Vivek Kasireddy wrote:
> > While looking for next holes suitable for an allocation, although,
> > it is highly unlikely, make sure that the DECLARE_NEXT_HOLE_ADDR
> > macro is using a valid node before it extracts the rb_node from it.
> 
> Was the need for this just a consequence of insufficient locking in the
> i915 patch?
[Kasireddy, Vivek] Partly, yes; but I figured since we are anyway doing
if (!entry || ..), it makes sense to dereference entry and extract the rb_node
after this check.

Thanks,
Vivek

> 
> Regards,
> 
> Tvrtko
> 
> >
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> > Cc: Christian König <christian.koenig@amd.com>
> > Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> > ---
> >   drivers/gpu/drm/drm_mm.c | 5 +++--
> >   1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
> > index 8257f9d4f619..499d8874e4ed 100644
> > --- a/drivers/gpu/drm/drm_mm.c
> > +++ b/drivers/gpu/drm/drm_mm.c
> > @@ -389,11 +389,12 @@ first_hole(struct drm_mm *mm,
> >   #define DECLARE_NEXT_HOLE_ADDR(name, first, last)			\
> >   static struct drm_mm_node *name(struct drm_mm_node *entry, u64 size)	\
> >   {									\
> > -	struct rb_node *parent, *node = &entry->rb_hole_addr;		\
> > +	struct rb_node *parent, *node;					\
> >   									\
> > -	if (!entry || RB_EMPTY_NODE(node))				\
> > +	if (!entry || RB_EMPTY_NODE(&entry->rb_hole_addr))		\
> >   		return NULL;						\
> >   									\
> > +	node = &entry->rb_hole_addr;					\
> >   	if (usable_hole_addr(node->first, size)) {			\
> >   		node = node->first;					\
> >   		while (usable_hole_addr(node->last, size))		\