linux-kernel - Re: [PATCH v4 4/6] mm/huge_memory: convert VM_BUG* to VM_WARN* in __folio

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Message-ID: <203a3260-45c2-4c82-9ec3-556599b17d53@lucifer.local>
Date: Fri, 18 Jul 2025 16:05:12 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Zi Yan <ziy@...dia.com>
Cc: David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Carpenter <dan.carpenter@...aro.org>,
        Antonio Quartulli <antonio@...delbit.com>,
        Hugh Dickins <hughd@...gle.com>,
        Kirill Shutemov <k.shutemov@...il.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
        Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
        Balbir Singh <balbirs@...dia.com>,
        Matthew Brost <matthew.brost@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/6] mm/huge_memory: convert VM_BUG* to VM_WARN* in
 __folio_split.

On Thu, Jul 17, 2025 at 10:29:58PM -0400, Zi Yan wrote:
> These VM_BUG* can be handled gracefully without crashing kernel.
>
> Signed-off-by: Zi Yan <ziy@...dia.com>

This LGTM, but obviously this is predicated on David being happy re: his reply
but from my side:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  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;
> +	}
>
>  	if (folio != page_folio(split_at) || folio != page_folio(lock_at))
>  		return -EINVAL;
> @@ -3766,7 +3772,11 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
>  		}
>
>  		if (folio_test_swapcache(folio)) {
> -			VM_BUG_ON(mapping);
> +			if (mapping) {
> +				VM_WARN_ON_ONCE_FOLIO(mapping, folio);
> +				ret = -EINVAL;
> +				goto fail;
> +			}
>
>  			swap_cache = swap_address_space(folio->swap);
>  			xa_lock(&swap_cache->i_pages);
> --
> 2.47.2
>