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

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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.shyti@xxxxxxxxxxxxxxx>
Signed-off-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>
---
 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


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