On 8/11/21 8:29 PM, Doug Berger wrote:
> When placing pages on a pcp list, migratetype values over
> MIGRATE_PCPTYPES get added to the MIGRATE_MOVABLE pcp list.
>
> However, the actual migratetype is preserved in the page and
> should not be changed to MIGRATE_MOVABLE or the page may end
> up on the wrong free_list.
Nice, how did you find out? Were there any user-visible effects? (Hint: which?
the changelog should say that so that the severity of the bug can be judged).
Otherwise I agree the bug is there and patch is fixing it. Thanks.
> Fixes: df1acc856923 ("mm/page_alloc: avoid conflating IRQs disabled with zone->lock")
> Signed-off-by: Doug Berger <opendmb@xxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
> mm/page_alloc.c | 25 ++++++++++++-------------
> 1 file changed, 12 insertions(+), 13 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 73704e836649..8addb4919f75 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3436,19 +3436,10 @@ void free_unref_page_list(struct list_head *list)
> * comment in free_unref_page.
> */
> migratetype = get_pcppage_migratetype(page);
> - if (unlikely(migratetype >= MIGRATE_PCPTYPES)) {
> - if (unlikely(is_migrate_isolate(migratetype))) {
> - list_del(&page->lru);
> - free_one_page(page_zone(page), page, pfn, 0,
> - migratetype, FPI_NONE);
> - continue;
> - }
> -
> - /*
> - * Non-isolated types over MIGRATE_PCPTYPES get added
> - * to the MIGRATE_MOVABLE pcp list.
> - */
> - set_pcppage_migratetype(page, MIGRATE_MOVABLE);
> + if (unlikely(is_migrate_isolate(migratetype))) {
> + list_del(&page->lru);
> + free_one_page(page_zone(page), page, pfn, 0, migratetype, FPI_NONE);
> + continue;
> }
>
> set_page_private(page, pfn);
> @@ -3458,7 +3449,15 @@ void free_unref_page_list(struct list_head *list)
> list_for_each_entry_safe(page, next, list, lru) {
> pfn = page_private(page);
> set_page_private(page, 0);
> +
> + /*
> + * Non-isolated types over MIGRATE_PCPTYPES get added
> + * to the MIGRATE_MOVABLE pcp list.
> + */
> migratetype = get_pcppage_migratetype(page);
> + if (unlikely(migratetype >= MIGRATE_PCPTYPES))
> + migratetype = MIGRATE_MOVABLE;
> +
> trace_mm_page_free_batched(page);
> free_unref_page_commit(page, pfn, migratetype, 0);
>
>
