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

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

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?

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))		\