Re: [PATCH v2 03/15] mm, swap: fix swap cahe index error when retrying reclaim

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 2025/9/6 03:13, Kairui Song wrote:
> From: Kairui Song <kasong@tencent.com>
> 
> The allocator will reclaim cached slots while scanning. Currently, it
> will try again if the reclaim found a folio that is already removed from
> the swap cache due to a race. But the following lookup will be using the
> wrong index. It won't cause any OOB issue since the swap cache index is
> truncated upon lookup, but it may lead to reclaiming of an irrelevant
> folio.
> 
> This should not cause a measurable issue, but we should fix it.
> 
> Fixes: fae8595505313 ("mm, swap: avoid reclaiming irrelevant swap cache")
> Signed-off-by: Kairui Song <kasong@tencent.com>
> ---

Good catch. LGTM.
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>

>   mm/swapfile.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 4b8ab2cb49ca..4c63fc62f4cb 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -240,13 +240,13 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si,
>   	 * Offset could point to the middle of a large folio, or folio
>   	 * may no longer point to the expected offset before it's locked.
>   	 */
> -	entry = folio->swap;
> -	if (offset < swp_offset(entry) || offset >= swp_offset(entry) + nr_pages) {
> +	if (offset < swp_offset(folio->swap) ||
> +	    offset >= swp_offset(folio->swap) + nr_pages) {
>   		folio_unlock(folio);
>   		folio_put(folio);
>   		goto again;
>   	}
> -	offset = swp_offset(entry);
> +	offset = swp_offset(folio->swap);
>   
>   	need_reclaim = ((flags & TTRS_ANYWAY) ||
>   			((flags & TTRS_UNMAPPED) && !folio_mapped(folio)) ||