Re: [PATCH] drm/i915/gem: Suppress oom warning in favour of ENOMEM to userspace

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Wed, Jun 26, 2024 at 04:33:18PM +0200, Nirmoy Das wrote:
> We report object allocation failures to userspace with ENOMEM
> so add __GFP_NOWARN to remove superfluous oom warnings.
> 
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/4936
> Cc: Andi Shyti <andi.shyti@linux.intel.com>
> Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_scatterlist.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_scatterlist.c b/drivers/gpu/drm/i915/i915_scatterlist.c
> index e93d2538f298..4d830740946d 100644
> --- a/drivers/gpu/drm/i915/i915_scatterlist.c
> +++ b/drivers/gpu/drm/i915/i915_scatterlist.c
> @@ -90,7 +90,7 @@ struct i915_refct_sgt *i915_rsgt_from_mm_node(const struct drm_mm_node *node,
>  
>  	GEM_BUG_ON(!max_segment);
>  
> -	rsgt = kmalloc(sizeof(*rsgt), GFP_KERNEL);
> +	rsgt = kmalloc(sizeof(*rsgt), GFP_KERNEL | __GFP_NOWARN);
>  	if (!rsgt)
>  		return ERR_PTR(-ENOMEM);

is it really safe?
I don't believe we can guarantee a good fallback plan here if allocation fails.
__i915_refct_sgt_init
might end up in a null dereference, no?!

>  
> @@ -104,7 +104,7 @@ struct i915_refct_sgt *i915_rsgt_from_mm_node(const struct drm_mm_node *node,
>  	}
>  
>  	if (sg_alloc_table(st, DIV_ROUND_UP_ULL(node->size, segment_pages),
> -			   GFP_KERNEL)) {
> +			   GFP_KERNEL | __GFP_NOWARN)) {
>  		i915_refct_sgt_put(rsgt);
>  		return ERR_PTR(-ENOMEM);
>  	}
> @@ -178,7 +178,7 @@ struct i915_refct_sgt *i915_rsgt_from_buddy_resource(struct ttm_resource *res,
>  	GEM_BUG_ON(list_empty(blocks));
>  	GEM_BUG_ON(!max_segment);
>  
> -	rsgt = kmalloc(sizeof(*rsgt), GFP_KERNEL);
> +	rsgt = kmalloc(sizeof(*rsgt), GFP_KERNEL | __GFP_NOWARN);
>  	if (!rsgt)
>  		return ERR_PTR(-ENOMEM);
>  
> @@ -190,7 +190,7 @@ struct i915_refct_sgt *i915_rsgt_from_buddy_resource(struct ttm_resource *res,
>  		return ERR_PTR(-E2BIG);
>  	}
>  
> -	if (sg_alloc_table(st, PFN_UP(res->size), GFP_KERNEL)) {
> +	if (sg_alloc_table(st, PFN_UP(res->size), GFP_KERNEL | __GFP_NOWARN)) {
>  		i915_refct_sgt_put(rsgt);
>  		return ERR_PTR(-ENOMEM);
>  	}
> -- 
> 2.42.0
>