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

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Hi Rodrigo,

On 6/26/2024 5:50 PM, Rodrigo Vivi wrote:
On Wed, Jun 26, 2024 at 05:36:43PM +0200, Nirmoy Das wrote:
    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: [1]https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/4936
    >Cc: Andi Shyti [2]<andi.shyti@xxxxxxxxxxxxxxx>
    >Signed-off-by: Nirmoy Das [3]<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.
doh! I had missunderstand the flag. Thanks for the confirmation.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>

BTW, what email clients are you using recently?

Using the same client, Thunderbird.


it is hard to parse your responses lately. Please check if it is really
sending/replying as text-only mode.

Thanks for notifying me. May be recent update changed some settings. I will check.


Nirmoy


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

References

    Visible links
    1. https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/4936
    2. mailto:andi.shyti@xxxxxxxxxxxxxxx
    3. mailto:nirmoy.das@xxxxxxxxx



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