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

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Message-ID: <C7CD4DE5-1C8C-460D-BB9B-1A11C8E038C6@nvidia.com>
Date: Tue, 30 Sep 2025 21:51:47 -0400
From: Zi Yan <ziy@...dia.com>
To: syzbot <syzbot+e6367ea2fdab6ed46056@...kaller.appspotmail.com>,
 syzkaller-bugs@...glegroups.com
Cc: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
 David Hildenbrand <david@...hat.com>, Luis Chamberlain <mcgrof@...nel.org>,
 akpm@...ux-foundation.org, linmiaohe@...wei.com,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, nao.horiguchi@...il.com
Subject: Re: [syzbot] [mm?] WARNING in memory_failure

On 29 Sep 2025, at 11:20, Zi Yan wrote:

> On 29 Sep 2025, at 7:08, Pankaj Raghav (Samsung) wrote:
>
>>>
>>> I want to change all the split functions in huge_mm.h and provide
>>> mapping_min_folio_order() to try_folio_split() in truncate_inode_partial_folio().
>>>
>>> Something like below:
>>>
>>> 1. no split function will change the given order;
>>> 2. __folio_split() will no longer give VM_WARN_ONCE when provided new_order
>>> is smaller than mapping_min_folio_order().
>>>
>>> In this way, for an LBS folio that cannot be split to order 0, split
>>> functions will return -EINVAL to tell caller that the folio cannot
>>> be split. The caller is supposed to handle the split failure.
>>
>> IIUC, we will remove warn on once but just return -EINVAL in __folio_split()
>> function if new_order < min_order like this:
>> ...
>> 		min_order = mapping_min_folio_order(folio->mapping);
>> 		if (new_order < min_order) {
>> -			VM_WARN_ONCE(1, "Cannot split mapped folio below min-order: %u",
>> -				     min_order);
>> 			ret = -EINVAL;
>> 			goto out;
>> 		}
>> ...
>>>
>>> WDYT?
>>>
>> I think it should be fine as along as we return an error if someone is
>> trying to split < min_order for file-backed folios.
>>

<snip>

>
> OK, I will send a proper patch to fix this. Thanks.

#syz test: git@...hub.com:x-y-z/linux-dev.git fix_split_page_min_order-for-kernelci

Best Regards,
Yan, Zi