Re: [PATCH 1/2] mm/page_alloc: Always remove pages from temporary list

[Vlastimil Babka]

On 11/18/22 11:17, Mel Gorman wrote:
> free_unref_page_list() has neglected to remove pages properly from the list
> of pages to free since forever. It works by coincidence because list_add
> happened to do the right thing adding the pages to just the PCP lists.
> However, a later patch added pages to either the PCP list or the zone list
> but only properly deleted the page from the list in one path leading to
> list corruption and a subsequent failure. As a preparation patch, always
> delete the pages from one list properly before adding to another.  On its
> own, this fixes nothing although it adds a fractional amount of overhead
> but is critical to the next patch.
> 
> Reported-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>

Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>

> ---
>  mm/page_alloc.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 218b28ee49ed..1ec54173b8d4 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3546,6 +3546,8 @@ void free_unref_page_list(struct list_head *list)
>  	list_for_each_entry_safe(page, next, list, lru) {
>  		struct zone *zone = page_zone(page);
>  
> +		list_del(&page->lru);
> +
>  		/* Different zone, different pcp lock. */
>  		if (zone != locked_zone) {
>  			if (pcp)