[PATCH 1/1] mm/migrate: fix list corruption in migration of non-LRU movable pages

[sunqiuyang]

From: Qiuyang Sun <sunqiuyang@xxxxxxxxxx>

Currently, after a page is migrated, it
1) has its PG_isolated flag cleared in move_to_new_page(), and
2) is deleted from its LRU list (cc->migratepages) in unmap_and_move().
However, between steps 1) and 2), the page could be isolated by another
thread in isolate_movable_page(), and added to another LRU list, leading
to list_del corruption later.

This patch fixes the bug by moving list_del into the critical section
protected by lock_page(), so that a page will not be isolated again before
it has been deleted from its LRU list.

Signed-off-by: Qiuyang Sun <sunqiuyang@xxxxxxxxxx>
---
 mm/migrate.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index a42858d..c58a606 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1124,6 +1124,8 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
 	/* Drop an anon_vma reference if we took one */
 	if (anon_vma)
 		put_anon_vma(anon_vma);
+	if (rc != -EAGAIN)
+		list_del(&page->lru);
 	unlock_page(page);
 out:
 	/*
@@ -1190,6 +1192,7 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
 			put_new_page(newpage, private);
 		else
 			put_page(newpage);
+		list_del(&page->lru);
 		goto out;
 	}
 
@@ -1200,14 +1203,6 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
 out:
 	if (rc != -EAGAIN) {
 		/*
-		 * A page that has been migrated has all references
-		 * removed and will be freed. A page that has not been
-		 * migrated will have kepts its references and be
-		 * restored.
-		 */
-		list_del(&page->lru);
-
-		/*
 		 * Compaction can migrate also non-LRU pages which are
 		 * not accounted to NR_ISOLATED_*. They can be recognized
 		 * as __PageMovable
-- 
1.8.3.1