Re: [PATCH] mm, slab: clean up slab->obj_exts always

[Harry Yoo]

On Fri, Apr 18, 2025 at 02:14:59PM +0800, Zhenhua Huang wrote:
> When memory allocation profiling is disabled at runtime or due to an
> error, shutdown_mem_profiling() is called: slab->obj_exts which
> previously allocated remains.
> It won't be cleared by unaccount_slab() because of
> mem_alloc_profiling_enabled() not true. It's incorrect, slab->obj_exts
> should always be cleaned up in unaccount_slab() to avoid following error:
> 
> [...]BUG: Bad page state in process...
> ..
> [...]page dumped because: page still charged to cgroup
> 
> Fixes: 21c690a349baa ("mm: introduce slabobj_ext to support slab object extensions")
> Signed-off-by: Zhenhua Huang <quic_zhenhuah@xxxxxxxxxxx>
> ---

Acked-by: Harry Yoo <harry.yoo@xxxxxxxxxx>

I reproduced the issue locally and confirmed that this patch fixes
the issue.

Tested-by: Harry Yoo <harry.yoo@xxxxxxxxxx>

By the way, I think this should probably be backported to -stable?

-- 
Cheers,
Harry / Hyeonggon

>  mm/slub.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index dac149df1be1..b42ce3a88806 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2023,7 +2023,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
>  	return 0;
>  }
>  
> -/* Should be called only if mem_alloc_profiling_enabled() */
> +/* Should be called if slab_obj_exts(slab) */
>  static noinline void free_slab_obj_exts(struct slab *slab)
>  {
>  	struct slabobj_ext *obj_exts;
> @@ -2592,7 +2592,11 @@ static __always_inline void account_slab(struct slab *slab, int order,
>  static __always_inline void unaccount_slab(struct slab *slab, int order,
>  					   struct kmem_cache *s)
>  {
> -	if (memcg_kmem_online() || need_slab_obj_ext())
> +	/*
> +	 * The slab object extensions should now be freed regardless of
> +	 * whether mem_alloc_profiling_enabled() or not now.
> +	 */
> +	if (memcg_kmem_online() || slab_obj_exts(slab))
>  		free_slab_obj_exts(slab);
>  
>  	mod_node_page_state(slab_pgdat(slab), cache_vmstat_idx(s),
> -- 
> 2.25.1
> 
>