Re: [PATCH v4 4/6] mm/huge_memory: convert VM_BUG* to VM_WARN* in __folio_split.

[Zi Yan]

On 18 Jul 2025, at 3:22, David Hildenbrand wrote:

> On 18.07.25 04:29, Zi Yan wrote:
>> These VM_BUG* can be handled gracefully without crashing kernel.
>>
>> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
>> ---
>>   mm/huge_memory.c | 16 +++++++++++++---
>>   1 file changed, 13 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index d36f7bdaeb38..d6ff5e8c89d7 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -3601,8 +3601,14 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
>>   	pgoff_t end;
>>   	bool is_hzp;
>>  -	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
>> -	VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
>> +	if (!folio_test_locked(folio)) {
>> +		VM_WARN_ON_ONCE_FOLIO(1, folio);
>> +		return -EINVAL;
>> +	}
>> +	if (!folio_test_large(folio)) {
>> +		VM_WARN_ON_ONCE_FOLIO(1, folio);
>> +		return -EINVAL;
>> +	}
>
> For cases that we handle gracefully you usually want to use
>
> if (WARN_ON_ONCE(..))

Got it.

>
> because then you get actually notified when that unexpected thing happens.
>
> I am not really sure if recovery is warranted here: smells like a straight VM_WARN_ON_ONCE_FOLIO() is sufficient, and catching this early during development that something is extremely off.

OK. I will update it to just VM_WARN_ON_ONCE_FOLIO().

Thanks.

Best Regards,
Yan, Zi