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Date:   Tue, 7 Jun 2022 14:14:45 +0200 (CEST)
From:   Christoph Lameter <cl@gentwo.de>
To:     Rongwei Wang <rongwei.wang@linux.alibaba.com>
cc:     David Rientjes <rientjes@google.com>, songmuchun@bytedance.com,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>, akpm@linux-foundation.org,
        vbabka@suse.cz, roman.gushchin@linux.dev, iamjoonsoo.kim@lge.com,
        penberg@kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] mm/slub: fix the race between validate_slab and
 slab_free
In-Reply-To: <9794df4f-3ffe-4e99-0810-a1346b139ce8@linux.alibaba.com>
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References: <20220529081535.69275-1-rongwei.wang@linux.alibaba.com> <YpNa4tB/jfW3MDyi@n2.us-central1-a.c.spheric-algebra-350919.internal> <ac9ba68f-9ee2-1611-9ff8-b486ed9c4df0@google.com> <alpine.DEB.2.22.394.2206021712530.2924@gentwo.de>
 <9794df4f-3ffe-4e99-0810-a1346b139ce8@linux.alibaba.com>
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On Fri, 3 Jun 2022, Rongwei Wang wrote:

> Recently, I am also find other ways to solve this. That case was provided by
> Muchun is useful (Thanks Muchun!). Indeed, it seems that use n->list_lock here
> is unwise. Actually, I'm not sure if you recognize the existence of such race?
> If all agrees this race, then the next question may be: do we want to solve
> this problem? or as David said, it would be better to deprecate validate
> attribute directly. I have no idea about it, hope to rely on your experience.
>
> In fact, I mainly want to collect your views on whether or how to fix this bug
> here. Thanks!


Well validate_slab() is rarely used and should not cause the hot paths to
incur performance penalties. Fix it in the validation logic somehow? Or
document the issue and warn that validation may not be correct if there
are current operations on the slab being validated.