Re: [syzbot] [mm?] WARNING in memory_failure

[Zi Yan]

On 2 Oct 2025, at 1:23, jane.chu@xxxxxxxxxx wrote:

> On 10/1/2025 7:04 PM, Zi Yan wrote:
>> On 1 Oct 2025, at 20:38, Zi Yan wrote:
>>
>>> On 1 Oct 2025, at 19:58, jane.chu@xxxxxxxxxx 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@xxxxxxxxxx/
>>>>
>>>> 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.
>>
>>
>>

<snip>

>
> There is a bug here,
>
> 		if (try_to_split_thp_page(p, new_order, false) || new_order) {
> 			res = -EHWPOISON;
> 			kill_procs_now(p, pfn, flags, folio);  <---
>
> If try_to_split_thp_page() succeeded on min_order, 'folio' should be retaken:  folio = page_folio(page) before moving on to kill_procs_now().

#syz test: https://github.com/x-y-z/linux-dev.git fix_split_page_min_order_and_opt_memory_failure_v2-for-kernelci

Best Regards,
Yan, Zi