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

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Message-ID: <2afee6bb-b2f0-4a86-ba8c-d33b0b477473@oracle.com>
Date: Wed, 1 Oct 2025 16:58:18 -0700
From: jane.chu@...cle.com
To: syzbot <syzbot+e6367ea2fdab6ed46056@...kaller.appspotmail.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,
        syzkaller-bugs@...glegroups.com, ziy@...dia.com
Subject: Re: [syzbot] [mm?] WARNING in memory_failure

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.
> 

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 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.

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.

thanks,
-jane