[PATCH v2] mm/page_isolation: don't putback unisolated page

[Miaohe Lin]

If __isolate_free_page() failed, due to zone watermark check, the page is
still on the free list. But this page will be put back to free list again
via __putback_isolated_page() now. This may trigger page->flags checks 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.

Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
v1->v2:
  Add VM_WARN_ON to catch unexpected isolating failure.
---
 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);
 			}
 		}
 	}
-- 
2.23.0