Re: [PATCH v3] mm/page_isolation: guard against possible putback unisolated page

[Vlastimil Babka <vbabka@suse.cz>]

On 9/14/21 13:45, Miaohe Lin wrote:
> Isolating a free page in an isolated pageblock is expected to always work
> as watermarks don't apply here. But if __isolate_free_page() failed, due
> to condition changes, the page will be left on the free list. And the page
> will be put back to free list again via __putback_isolated_page(). This may
> trigger VM_BUG_ON_PAGE() on page->flags checking 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. Add a VM_WARN_ON() to
> complain about this change.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
> v1->v2:
>   Add VM_WARN_ON to catch unexpected isolating failure.
> v2->v3:
>   Change the patch description+subject and remove Fixes.
> ---
>  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);
>  			}
>  		}
>  	}
>