linux-kernel - Re: [PATCH v2] mm/page_isolation: don't putback unisolated page

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Date:   Mon, 13 Sep 2021 14:15:25 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     jhubbard@...dia.com, vbabka@...e.cz, iamjoonsoo.kim@....com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/page_isolation: don't putback unisolated page

On 13.09.21 13:50, Miaohe Lin wrote:
> If __isolate_free_page() failed, due to zone watermark check, the page is
> still on the free list. But this page will be put back to free list again
> via __putback_isolated_page() now. This may trigger page->flags checks in
> __free_one_page() if PageReported is set. Or we will corrupt the free list
> because list_add() will be called for pages already on another list.
> 
> Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock")
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
> v1->v2:
>    Add VM_WARN_ON to catch unexpected isolating failure.
> ---
>   mm/page_isolation.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index f93cc63d8fa1..f67c4c70f17f 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -94,8 +94,13 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
>   			buddy = page + (buddy_pfn - pfn);
>   
>   			if (!is_migrate_isolate_page(buddy)) {
> -				__isolate_free_page(page, order);
> -				isolated_page = true;
> +				isolated_page = !!__isolate_free_page(page, order);
> +				/*
> +				 * Isolating a free page in an isolated pageblock
> +				 * is expected to always work as watermarks don't
> +				 * apply here.
> +				 */
> +				VM_WARN_ON(!isolated_page);


Didn't we discuss that this can never happen?

In that case, the patch description+subject needs updating and the 
"Fixes" line would be wrong.

>   			}
>   		}
>   	}
> 


-- 
Thanks,

David / dhildenb