[PATCH v3] mm/page_isolation: fix potential missing call to unset_migratetype_isolate()

[Miaohe Lin]

In start_isolate_page_range() undo path, pfn_to_online_page() just checks
the first pfn in a pageblock while __first_valid_page() will traverse the
pageblock until the first online pfn is found. So we may miss the call to
unset_migratetype_isolate() in undo path and pages will remain isolated
unexpectedly. Fix this by calling undo_isolate_page_range() and this will
also help to simplify the code further. Note we shouldn't ever trigger it
because MAX_ORDER-1 aligned pfn ranges shouldn't contain memory holes now.

Fixes: 2ce13640b3f4 ("mm: __first_valid_page skip over offline pages")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
v1->v2:
  Simplify the code further per David Hildenbrand.
v2->v3:
  remove unneeded cc stable.
---
 mm/page_isolation.c | 20 +++-----------------
 1 file changed, 3 insertions(+), 17 deletions(-)

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index a95c2c6562d0..f93cc63d8fa1 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -183,7 +183,6 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
 			     unsigned migratetype, int flags)
 {
 	unsigned long pfn;
-	unsigned long undo_pfn;
 	struct page *page;
 
 	BUG_ON(!IS_ALIGNED(start_pfn, pageblock_nr_pages));
@@ -193,25 +192,12 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
 	     pfn < end_pfn;
 	     pfn += pageblock_nr_pages) {
 		page = __first_valid_page(pfn, pageblock_nr_pages);
-		if (page) {
-			if (set_migratetype_isolate(page, migratetype, flags)) {
-				undo_pfn = pfn;
-				goto undo;
-			}
+		if (page && set_migratetype_isolate(page, migratetype, flags)) {
+			undo_isolate_page_range(start_pfn, pfn, migratetype);
+			return -EBUSY;
 		}
 	}
 	return 0;
-undo:
-	for (pfn = start_pfn;
-	     pfn < undo_pfn;
-	     pfn += pageblock_nr_pages) {
-		struct page *page = pfn_to_online_page(pfn);
-		if (!page)
-			continue;
-		unset_migratetype_isolate(page, migratetype);
-	}
-
-	return -EBUSY;
 }
 
 /*
-- 
2.23.0