linux-kernel - Re: [PATCH] mm: page_alloc: validate buddy before check its migratetype.

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Date:   Wed, 30 Mar 2022 18:29:18 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Zi Yan <zi.yan@...t.com>
Cc:     Zi Yan <ziy@...dia.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Rapoport <rppt@...nel.org>,
        Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: page_alloc: validate buddy before check its
 migratetype.

On Wed, 30 Mar 2022 18:12:38 -0400
Zi Yan <zi.yan@...t.com> wrote:

> From: Zi Yan <ziy@...dia.com>
> 
> Whenever a buddy page is found, page_is_buddy() should be called to
> check its validity. Add the missing check during pageblock merge check.
> 
> Fixes: 1dd214b8f21c ("mm: page_alloc: avoid merging non-fallbackable pageblocks with others")

Link: https://lore.kernel.org/all/20220330154208.71aca532@gandalf.local.home/

> 
> Reported-by: Steven Rostedt <rostedt@...dmis.org>

Tested-by: Steven Rostedt (Google) <rostedt@...dmis.org>

-- Steve

> Signed-off-by: Zi Yan <ziy@...dia.com>
> ---
>  mm/page_alloc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index bdc8f60ae462..6c6af8658775 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1108,6 +1108,9 @@ static inline void __free_one_page(struct page *page,
>  
>  		buddy_pfn = __find_buddy_pfn(pfn, order);
>  		buddy = page + (buddy_pfn - pfn);
> +
> +		if (!page_is_buddy(page, buddy, order))
> +			goto done_merging;
>  		buddy_mt = get_pageblock_migratetype(buddy);
>  
>  		if (migratetype != buddy_mt