linux-kernel - Re: [PATCH v2] mm: kfence: fix objcgs vector allocation

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Date:   Mon, 28 Mar 2022 17:43:07 +0200
From:   Marco Elver <elver@...gle.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     glider@...gle.com, dvyukov@...gle.com, akpm@...ux-foundation.org,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, duanxiongchun@...edance.com
Subject: Re: [PATCH v2] mm: kfence: fix objcgs vector allocation

On Mon, 28 Mar 2022 at 15:28, Muchun Song <songmuchun@...edance.com> wrote:
>
> If the kfence object is allocated to be used for objects vector, then
> this slot of the pool eventually being occupied permanently since
> the vector is never freed.  The solutions could be 1) freeing vector
> when the kfence object is freed or 2) allocating all vectors statically.
> Since the memory consumption of object vectors is low, it is better to
> chose 2) to fix the issue and it is also can reduce overhead of vectors
> allocating in the future.
>
> Fixes: d3fb45f370d9 ("mm, kfence: insert KFENCE hooks for SLAB")
> Signed-off-by: Muchun Song <songmuchun@...edance.com>

Reviewed-by: Marco Elver <elver@...gle.com>

Btw, how did you test this?

Thanks,
-- Marco

> ---
> v2:
>  - Fix compiler error reported by kernel test robot <lkp@...el.com>.
>
>  mm/kfence/core.c   | 11 ++++++++++-
>  mm/kfence/kfence.h |  3 +++
>  2 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index 13128fa13062..d4c7978cd75e 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -555,6 +555,8 @@ static bool __init kfence_init_pool(void)
>          * enters __slab_free() slow-path.
>          */
>         for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
> +               struct slab *slab = page_slab(&pages[i]);
> +
>                 if (!i || (i % 2))
>                         continue;
>
> @@ -562,7 +564,11 @@ static bool __init kfence_init_pool(void)
>                 if (WARN_ON(compound_head(&pages[i]) != &pages[i]))
>                         goto err;
>
> -               __SetPageSlab(&pages[i]);
> +               __folio_set_slab(slab_folio(slab));
> +#ifdef CONFIG_MEMCG
> +               slab->memcg_data = (unsigned long)&kfence_metadata[i / 2 - 1].objcg |
> +                                  MEMCG_DATA_OBJCGS;
> +#endif
>         }
>
>         /*
> @@ -938,6 +944,9 @@ void __kfence_free(void *addr)
>  {
>         struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);
>
> +#ifdef CONFIG_MEMCG
> +       KFENCE_WARN_ON(meta->objcg);
> +#endif
>         /*
>          * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing
>          * the object, as the object page may be recycled for other-typed
> diff --git a/mm/kfence/kfence.h b/mm/kfence/kfence.h
> index 2a2d5de9d379..9a6c4b1b12a8 100644
> --- a/mm/kfence/kfence.h
> +++ b/mm/kfence/kfence.h
> @@ -89,6 +89,9 @@ struct kfence_metadata {
>         struct kfence_track free_track;
>         /* For updating alloc_covered on frees. */
>         u32 alloc_stack_hash;
> +#ifdef CONFIG_MEMCG
> +       struct obj_cgroup *objcg;
> +#endif
>  };
>
>  extern struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS];
> --
> 2.11.0
>