linux-kernel - Re: [PATCH mm] kfence, slab: fix cache_alloc_debugcheck

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Message-Id: <20210304173132.6696eb2a357edf835a5033ee@linux-foundation.org>
Date:   Thu, 4 Mar 2021 17:31:32 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     Dmitriy Vyukov <dvyukov@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Marco Elver <elver@...gle.com>
Subject: Re: [PATCH mm] kfence, slab: fix cache_alloc_debugcheck_after() for
 bulk allocations

On Thu, 4 Mar 2021 22:05:48 +0100 Alexander Potapenko <glider@...gle.com> wrote:

> On Thu, Mar 4, 2021 at 9:53 PM Marco Elver <elver@...gle.com> wrote:
> >
> > cache_alloc_debugcheck_after() performs checks on an object, including
> > adjusting the returned pointer. None of this should apply to KFENCE
> > objects. While for non-bulk allocations, the checks are skipped when we
> > allocate via KFENCE, for bulk allocations cache_alloc_debugcheck_after()
> > is called via cache_alloc_debugcheck_after_bulk().
> 
> @Andrew, is this code used by anyone?
> As far as I understand, it cannot be enabled by any config option, so
> nobody really tests it.
> If it is still needed, shall we promote #if DEBUGs in slab.c to a
> separate config option, or maybe this code can be safely removed?

It's all used:

#ifdef CONFIG_DEBUG_SLAB
#define	DEBUG		1
#define	STATS		1
#define	FORCED_DEBUG	1
#else
#define	DEBUG		0
#define	STATS		0
#define	FORCED_DEBUG	0
#endif