linux-kernel - Re: [PATCH] slub: fix unreclaimable slab stat for bulk free

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Date:   Tue, 3 Aug 2021 16:29:16 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        Shakeel Butt <shakeelb@...gle.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Michal Hocko <mhocko@...e.com>, Roman Gushchin <guro@...com>,
        Wang Hai <wanghai38@...wei.com>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] slub: fix unreclaimable slab stat for bulk free

On 8/3/21 4:24 PM, Kefeng Wang wrote:
> 
> On 2021/7/29 22:03, Shakeel Butt wrote:
>> On Wed, Jul 28, 2021 at 11:52 PM Kefeng Wang <wangkefeng.wang@...wei.com> wrote:
>>>
>>> On 2021/7/28 23:53, Shakeel Butt wrote:
>> I don't have a strong opinion on this. Please send a patch with
>> reasoning if you want WARN_ON_ONCE here.
> 
> Ok, we met a BUG_ON(!PageCompound(page)) in kfree() twice in lts4.4, we are
> still debugging it.
> 
> It's different to analyses due to no vmcore, and can't be reproduced.
> 
> WARN_ON() here could help us to notice the issue.
> 
> Also is there any experience or known fix/way to debug this kinds of issue?
> memory corruption?

This would typically be a use-after-free/double-free - a problem of the slab
user, not slab itself.

> Any suggestion will be appreciated, thanks.

debug_pagealloc could help to catch a use-after-free earlier

> 
>> .
>>