linux-kernel - Re: [PATCH 1/1] mm: kfence: skip kmemleak alloc in kfence

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Date:   Thu, 23 Jun 2022 13:59:59 +0200
From:   Marco Elver <elver@...gle.com>
To:     yee.lee@...iatek.com
Cc:     linux-kernel@...r.kernel.org,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "open list:KFENCE" <kasan-dev@...glegroups.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH 1/1] mm: kfence: skip kmemleak alloc in kfence_pool

On Thu, 23 Jun 2022 at 13:20, yee.lee via kasan-dev
<kasan-dev@...glegroups.com> wrote:
>
> From: Yee Lee <yee.lee@...iatek.com>
>
> Use MEMBLOCK_ALLOC_NOLEAKTRACE to skip kmemleak registration when
> the kfence pool is allocated from memblock. And the kmemleak_free
> later can be removed too.

Is this purely meant to be a cleanup and non-functional change?

> Signed-off-by: Yee Lee <yee.lee@...iatek.com>
>
> ---
>  mm/kfence/core.c | 18 ++++++++----------
>  1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index 4e7cd4c8e687..0d33d83f5244 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -600,14 +600,6 @@ static unsigned long kfence_init_pool(void)
>                 addr += 2 * PAGE_SIZE;
>         }
>
> -       /*
> -        * The pool is live and will never be deallocated from this point on.
> -        * Remove the pool object from the kmemleak object tree, as it would
> -        * otherwise overlap with allocations returned by kfence_alloc(), which
> -        * are registered with kmemleak through the slab post-alloc hook.
> -        */
> -       kmemleak_free(__kfence_pool);

This appears to only be a non-functional change if the pool is
allocated early. If the pool is allocated late using page-alloc, then
there'll not be a kmemleak_free() on that memory and we'll have the
same problem.