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

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Message-ID: <06874ec1-5e92-4988-95ed-e4fdbb041845@redhat.com>
Date: Mon, 29 Sep 2025 18:13:47 +0200
From: David Hildenbrand <david@...hat.com>
To: Zi Yan <ziy@...dia.com>, "Pankaj Raghav (Samsung)"
 <kernel@...kajraghav.com>
Cc: Luis Chamberlain <mcgrof@...nel.org>,
 syzbot <syzbot+e6367ea2fdab6ed46056@...kaller.appspotmail.com>,
 akpm@...ux-foundation.org, linmiaohe@...wei.com,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, nao.horiguchi@...il.com,
 syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] WARNING in memory_failure

On 29.09.25 17:20, 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.
>>
>>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>>> index f327d62fc985..e15c3ca07e33 100644
>>> --- a/include/linux/huge_mm.h
>>> +++ b/include/linux/huge_mm.h
>>> @@ -387,34 +387,16 @@ int folio_split(struct folio *folio, unsigned int new_order, struct page *page,
>>>    * Return: 0: split is successful, otherwise split failed.
>>>    */
>>>   static inline int try_folio_split(struct folio *folio, struct page *page,
>>> -		struct list_head *list)
>>> +		struct list_head *list, unsigned int order)
>>>   {
> 
> OK, I will send a proper patch to fix this. Thanks.

Thanks!

-- 
Cheers

David / dhildenb