linux-kernel - Re: [PATCH] mm: page_isolation: use compound_nr() correctly in isolate_single

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Message-ID: <YpXYP9cJJo7dj12E@localhost.localdomain>
Date:   Tue, 31 May 2022 10:56:31 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Zi Yan <ziy@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Qian Cai <quic_qiancai@...cinc.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Eric Ren <renzhengeek@...il.com>,
        Mike Rapoport <rppt@...nel.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: [PATCH] mm: page_isolation: use compound_nr() correctly in
 isolate_single_pageblock()

On Mon, May 30, 2022 at 10:44:50PM -0400, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.com>
> 
> When compound_nr(page) was used, page was not guaranteed to be the head
> of the compound page and it could cause an infinite loop. Fix it by calling
> it on the head page.
> 
> Fixes: b2c9e2fbba32 ("mm: make alloc_contig_range work at pageblock granularity")
> Reported-by: Anshuman Khandual <anshuman.khandual@....com>
> Link: https://lore.kernel.org/linux-mm/20220530115027.123341-1-anshuman.khandual@arm.com/
> Signed-off-by: Zi Yan <ziy@...dia.com>

Reviewed-by: Oscar Salvador <osalvador@...e.de>

> ---
>  mm/page_isolation.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 6021f8444b5a..d200d41ad0d3 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -385,9 +385,9 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
>  		 * above do the rest. If migration is not possible, just fail.
>  		 */
>  		if (PageCompound(page)) {
> -			unsigned long nr_pages = compound_nr(page);
>  			struct page *head = compound_head(page);
>  			unsigned long head_pfn = page_to_pfn(head);
> +			unsigned long nr_pages = compound_nr(head);
>  
>  			if (head_pfn + nr_pages <= boundary_pfn) {
>  				pfn = head_pfn + nr_pages;
> -- 
> 2.35.1
> 

-- 
Oscar Salvador
SUSE Labs