Re: [PATCH] slab: Add allow_spin check to eliminate kmemleak warnings

[Harry Yoo]

On Tue, Sep 30, 2025 at 06:38:31AM +0000, ranxiaokai627@xxxxxxx wrote:
> From: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
> 
> In slab_post_alloc_hook(), kmemleak check is skipped when
> gfpflags_allow_spinning() returns false since commit 13d872ade8be
> ("slab: Introduce kmalloc_nolock() and kfree_nolock().").
> Therefore, unconditionally calling kmemleak_not_leak() in
> alloc_slab_obj_exts() would trigger the following warning:

Good catch.

> kmemleak: Trying to color unknown object at 0xffff8881057f5000 as Grey
> Call Trace:
>  alloc_slab_obj_exts+0x1b5/0x370
>  __alloc_tagging_slab_alloc_hook+0x9f/0x2d0
>  __kmalloc_cache_noprof+0x1c4/0x5c0
>  __set_page_owner+0x10d/0x1c0
>  post_alloc_hook+0x84/0xf0
>  get_page_from_freelist+0x73b/0x1380
>  __alloc_frozen_pages_noprof+0x110/0x2c0
>  alloc_pages_mpol+0x44/0x140
>  alloc_slab_page+0xac/0x150
>  allocate_slab+0x78/0x3a0
>  ___slab_alloc+0x76b/0xed0
>  __slab_alloc.constprop.0+0x5a/0xb0
> 
> Add the allow_spin check in alloc_slab_obj_exts() to
> eliminate the above warning.
> 
> Fixes: 13d872ade8be ("slab: Introduce kmalloc_nolock() and kfree_nolock().")

The commit hash in the tag and commit message will be adjusted after -rc1
when picking up this patch.

> Signed-off-by: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
> ---

Looks good to me,
Reviewed-by: Harry Yoo <harry.yoo@xxxxxxxxxx>

-- 
Cheers,
Harry / Hyeonggon

>  mm/slub.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 09cbe580842c..a76275f4870a 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2145,7 +2145,8 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
>  		return 0;
>  	}
>  
> -	kmemleak_not_leak(vec);
> +	if (allow_spin)
> +		kmemleak_not_leak(vec);
>  	return 0;
>  }
>  
> -- 
> 2.25.1