linux-kernel - Re: Possible regression in "slab, slub: skip unnecessary kasan_cache

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Date:   Tue, 19 Jun 2018 22:17:25 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     aryabinin@...tuozzo.com
Cc:     Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, cl@...ux.com,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev@...glegroups.com, Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Shakeel Butt <shakeelb@...gle.com>
Subject: Re: Possible regression in "slab, slub: skip unnecessary kasan_cache_shutdown()"

Hi Andrey,

On Tue, Jun 19, 2018 at 7:33 PM Andrey Ryabinin <aryabinin@...tuozzo.com> wrote:
> What's the status of CONFIG_SLUB_DEBUG in your config?
>
> AFAICS __kmem_cache_empty() is broken for CONFIG_SLUB_DEBUG=n. We use slabs_node() there
> which is always 0 for CONFIG_SLUB_DEBUG=n.
>
> The problem seems not limited to __kmem_cache_empty(), __kmem_cache_shutdown() and __kmem_cache_shrink()
> are also rely on correctness of the slabs_node(). Presumably this might cause some problems while
> destroying memcg kmem caches.

CONFIG_SLUB_DEBUG is not set in the crash I sent.

Enabling it "fixes" the problem! This either means that KASAN+SLUB
should enable SLUB_DEBUG, or the extra overhead from SLUB_DEBUG is
just making the bug more rare but not actually eliminating it.

Jason