From: Miaohe Lin <linmiaohe@xxxxxxxxxx> Subject: mm/page_isolation: guard against possible putback unisolated page 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. Link: https://lkml.kernel.org/r/20210914114508.23725-1-linmiaohe@xxxxxxxxxx Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock") Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: John Hubbard <jhubbard@xxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page_isolation.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) --- a/mm/page_isolation.c~mm-page_isolation-guard-against-possible-putback-unisolated-page +++ a/mm/page_isolation.c @@ -94,8 +94,13 @@ static void unset_migratetype_isolate(st 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); } } } _
