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

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Message-ID: <22bc228e-4598-4b5d-ab5d-f9f493a4d961@redhat.com>
Date: Mon, 8 Sep 2025 13:45:18 +0200
From: David Hildenbrand <david@...hat.com>
To: Kairui Song <kasong@...cent.com>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Matthew Wilcox <willy@...radead.org>, Hugh Dickins <hughd@...gle.com>,
 Chris Li <chrisl@...nel.org>, Barry Song <baohua@...nel.org>,
 Baoquan He <bhe@...hat.com>, Nhat Pham <nphamcs@...il.com>,
 Kemeng Shi <shikemeng@...weicloud.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Ying Huang <ying.huang@...ux.alibaba.com>,
 Johannes Weiner <hannes@...xchg.org>, Yosry Ahmed <yosryahmed@...gle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 03/15] mm, swap: fix swap cahe index error when
 retrying reclaim

On 05.09.25 21:13, Kairui Song wrote:
> From: Kairui Song <kasong@...cent.com>

Subject: s/cahe/cache/

> 
> The allocator will reclaim cached slots while scanning. Currently, it
> will try again if the reclaim found a folio that is already removed from

s/the reclaim/reclaim/

> 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@...cent.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)) ||


Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers

David / dhildenb