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

[David Hildenbrand]

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(..))

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.

--
Cheers,

David / dhildenb