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Subject[PATCH 1/1] mm/migrate: fix list corruption in migration of non-LRU movable pages
Date
From: Qiuyang Sun <sunqiuyang@huawei.com>

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@huawei.com>
---
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
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