Re: [PATCH v2 02/13] mm/slub: skip handle_failed_objexts_alloc() with profiling disabled

[Harry Yoo]

On 7/20/26 11:16 PM, Vlastimil Babka (SUSE) wrote:
> The function might get called with memory allocation profiling disabled,
> when the obj_ext array is allocated for objcg pointers only. The
> handling is however unnecessary in that case, so skip it.
> 
> This would otherwise become a real bug later, as pointed out by sashiko.
> For now it's just an optimization.
> 
> Link: https://sashiko.dev/#/patchset/20260715-b4-objext_split-v1-0-9a49c4ccf4c3@xxxxxxxxxx?part=10
> Signed-off-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>
> ---
>  mm/slub.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 76acb78f2655..95fa6fbad11a 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2101,15 +2101,16 @@ static inline bool mark_failed_objexts_alloc(struct slab *slab)
>  static inline void handle_failed_objexts_alloc(unsigned long obj_exts,
>  			struct slabobj_ext *vec, unsigned int objects)
>  {
> +	if (!mem_alloc_profiling_enabled())
> +		return;

This looks racy.

Can we instead do this later in the series depending on
slab_obj_ext_has_codetag_key's value?

>  	/*
>  	 * If vector previously failed to allocate then we have live
>  	 * objects with no tag reference. Mark all references in this
>  	 * vector as empty to avoid warnings later on.
>  	 */
>  	if (obj_exts == OBJEXTS_ALLOC_FAIL) {
> -		unsigned int i;
> -
> -		for (i = 0; i < objects; i++)
> +		for (unsigned int i = 0; i < objects; i++)
>  			set_codetag_empty(&vec[i].ref);
>  	}
>  }
> 

-- 
Cheers,
Harry / Hyeonggon

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