[PATCH 3/4] mm/rmap: fix new bug: premature return from page_mlock_one()

Hugh Dickins
2021-07-07T20:11:30Z

In the unlikely race case that page_mlock_one() finds VM_LOCKED has been
cleared by the time it got page table lock, page_vma_mapped_walk_done()
must be called before returning, either explicitly, or by a final call
to page_vma_mapped_walk() - otherwise the page table remains locked.

Fixes: cd62734ca60d ("mm/rmap: split try_to_munlock from try_to_unmap")
Signed-off-by: Hugh Dickins <hughd@google.com>
---
mm/rmap.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 0e83c3be8568..1235368f0628 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1990,14 +1990,13 @@ static bool page_mlock_one(struct page *page, struct vm_area_struct *vma,
* this function is never called when PageDoubleMap().
*/
mlock_vma_page(page);
+ /*
+ * No need to scan further once the page is marked
+ * as mlocked.
+ */
page_vma_mapped_walk_done(&pvmw);
+ return false;
}
-
- /*
- * no need to continue scanning other vma's if the page has
- * been locked.
- */
- return false;
}

return true;
--
2.26.2