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

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Message-ID: <46ca5661-4bd1-6733-0140-d6e6dea1ab33@virtuozzo.com>
Date:   Tue, 19 Jun 2018 20:34:22 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>,
        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()"



On 06/19/2018 05:51 AM, Jason A. Donenfeld wrote:
> Hello Shakeel,
> 
> It may be the case that f9e13c0a5a33d1eaec374d6d4dab53a4f72756a0 has
> introduced a regression. I've bisected a failing test to this commit,
> and after staring at the my code for a long time, I'm unable to find a
> bug that this commit might have unearthed. Rather, it looks like this
> commit introduces a performance optimization, rather than a
> correctness fix, so it seems that whatever test case is failing is
> likely an incorrect failure. Does that seem like an accurate
> possibility to you?
> 
> Below is a stack trace when things go south. Let me know if you'd like
> to run my test suite, and I can send additional information.
> 
> Regards,
> Jason
> 
> 

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.