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Subject: Re: [PATCH] slub: fix unreclaimable slab stat for bulk free
To:     Kefeng Wang <wangkefeng.wang@huawei.com>,
        Shakeel Butt <shakeelb@google.com>
Cc:     Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Michal Hocko <mhocko@suse.com>, Roman Gushchin <guro@fb.com>,
        Wang Hai <wanghai38@huawei.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
References: <20210728155354.3440560-1-shakeelb@google.com>
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 <35a0b75a-f348-d21c-4ff4-fadba0c4db02@huawei.com>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <43cf4e71-4dd4-dc37-a70f-553fe5cba126@suse.cz>
Date:   Tue, 3 Aug 2021 16:29:16 +0200
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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@huawei.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

> 
>> .
>>