linux-kernel - Re: [syzbot] [mm?] WARNING in memory

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Message-ID: <A4321695-9F12-4C7C-ACC9-72FD84B6DB2C@nvidia.com>
Date: Wed, 01 Oct 2025 22:04:43 -0400
From: Zi Yan <ziy@...dia.com>
To: syzbot <syzbot+e6367ea2fdab6ed46056@...kaller.appspotmail.com>,
 syzkaller-bugs@...glegroups.com
Cc: jane.chu@...cle.com, akpm@...ux-foundation.org, david@...hat.com,
 kernel@...kajraghav.com, linmiaohe@...wei.com, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, mcgrof@...nel.org, nao.horiguchi@...il.com
Subject: Re: [syzbot] [mm?] WARNING in memory_failure

On 1 Oct 2025, at 20:38, Zi Yan wrote:

> On 1 Oct 2025, at 19:58, jane.chu@...cle.com wrote:
>
>> Hi, Zi Yan,
>>
>> On 9/30/2025 9:51 PM, syzbot wrote:
>>> Hello,
>>>
>>> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
>>> lost connection to test machine
>>>
>>>
>>>
>>> Tested on:
>>>
>>> commit:         d8795075 mm/huge_memory: do not change split_huge_page..
>>> git tree:       https://github.com/x-y-z/linux-dev.git fix_split_page_min_order-for-kernelci
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=17ce96e2580000
>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=714d45b6135c308e
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=e6367ea2fdab6ed46056
>>> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
>>> userspace arch: arm64
>>>
>>> Note: no patches were applied.
>>>
>>
>
> Thank you for looking into this.
>
>> My hunch is that
>> https://github.com/x-y-z/linux-dev.git fix_split_page_min_order-for-kernelci
>> alone is not enough.  Perhaps on ARM64, the page cache pages of /dev/nullb0 in
> Yes, it only has the first patch, which fails a split if it cannot be
> split to the intended order (order-0 in this case).
>
>
>> the test case are probably with min_order > 0, therefore THP split fails, as the console message show:
>> [  200.378989][T18221] Memory failure: 0x124d30: recovery action for unsplit thp: Failed
>>
>> With lots of poisoned THP pages stuck in the page cache, OOM could trigger too soon.
>
> That is my understanding too. Thanks for the confirmation.
>
>>
>> I think it's worth to try add the additional changes I suggested earlier -
>> https://lore.kernel.org/lkml/7577871f-06be-492d-b6d7-8404d7a045e0@oracle.com/
>>
>> So that in the madvise HWPOISON cases, large huge pages are splitted to smaller huge pages, and most of them remain usable in the page cache.
>
> Yep, I am going to incorporate your suggestion as the second patch and make
> syzbot check it again.


#syz test: https://github.com/x-y-z/linux-dev.git fix_split_page_min_order_and_opt_memory_failure-for-kernelci


--
Best Regards,
Yan, Zi