linux-kernel - Re: [PATCH 2/2] mm/debug: Fix parameter passed to page_mapcount_is

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Message-ID: <6ef83b28-5f01-4405-a25e-0bd59e071118@redhat.com>
Date: Fri, 21 Mar 2025 11:14:16 +0100
From: David Hildenbrand <david@...hat.com>
To: Gavin Shan <gshan@...hat.com>, linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
 willy@...radead.org, vbabka@...e.cz, osalvador@...e.de, gehao@...inos.cn,
 shan.gavin@...il.com
Subject: Re: [PATCH 2/2] mm/debug: Fix parameter passed to
 page_mapcount_is_type()

On 21.03.25 06:31, Gavin Shan wrote:
> As the comments of page_mapcount_is_type() indicate, the parameter passed
> to the function should be one more than page->__mapcount. However,
> page->__mapcount is passed to the function by commit 4ffca5a96678
> ("mm: support only one page_type per page") where page_type_has_type()
> is replaced by page_mapcount_is_type(), but the parameter isn't adjusted.
> 
> Fix the parameter passed to page_mapcount_is_type() to be (page->__mapcount
> + 1).
> 
> Fixes: 4ffca5a96678 ("mm: support only one page_type per page")
> Cc: stable@...r.kernel.org # v6.12+
> Signed-off-by: Gavin Shan <gshan@...hat.com>
> ---
>   mm/debug.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/debug.c b/mm/debug.c
> index 8d2acf432385..b6bd9555ec7b 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -71,10 +71,10 @@ static void __dump_folio(struct folio *folio, struct page *page,
>   		unsigned long pfn, unsigned long idx)
>   {
>   	struct address_space *mapping = folio_mapping(folio);
> -	int mapcount = atomic_read(&page->_mapcount);
> +	int mapcount = atomic_read(&page->_mapcount) + 1;
>   	char *type = "";
>   
> -	mapcount = page_mapcount_is_type(mapcount) ? 0 : mapcount + 1;
> +	mapcount = page_mapcount_is_type(mapcount) ? 0 : mapcount;
>   	pr_warn("page: refcount:%d mapcount:%d mapping:%p index:%#lx pfn:%#lx\n",
>   			folio_ref_count(folio), mapcount, mapping,
>   			folio->index + idx, pfn);

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


-- 
Cheers,

David / dhildenb