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

[Nirmoy Das]

Hi Rodrigo,

On 6/26/2024 5:24 PM, Rodrigo Vivi wrote:
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.sh...@linux.intel.com>
Signed-off-by: Nirmoy Das<nirmoy....@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?!

Kernel is now returning ENOMEM and also throwing a oom warning stack. 
With __GFP_NOWARN

the oom warning stack won't be there in the dmesg but userspace will 
still get ENOMEM as expected.

Let me know if got your question correctly.

Regards,

Nirmoy


  
@@ -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