On Fri, Dec 04, 2020 at 12:22:37AM +0800, Muchun Song wrote: > The max order page has no buddy page and never merge to other order. > So isolating and then freeing it is pointless. And if order == MAX_ORDER > - 1, then the buddy can actually be a !pfn_valid() in some corner case? > pfn_valid_within(buddy_pfn) that follows would only catch it on archs > with holes in zone. Then is_migrate_isolate_page(buddy) might access an > invalid buddy. So this is also a bug fix. > > Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock") > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx> > Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx> > --- > Changes in v2: > - Add Fixes tag in the commit log. > > mm/page_isolation.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/page_isolation.c b/mm/page_isolation.c > index a254e1f370a3..bddf788f45bf 100644 > --- a/mm/page_isolation.c > +++ b/mm/page_isolation.c > @@ -88,7 +88,7 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype) > */ > if (PageBuddy(page)) { > order = buddy_order(page); > - if (order >= pageblock_order) { > + if (order >= pageblock_order && order < MAX_ORDER - 1) { > pfn = page_to_pfn(page); > buddy_pfn = __find_buddy_pfn(pfn, order); > buddy = page + (buddy_pfn - pfn); > -- > 2.11.0 > > -- Oscar Salvador SUSE L3