[PATCH] mm/rmap: Fix potential pte_unmap on an not mapped pte

[Miaohe Lin]

For PMD-mapped page (usually THP), pvmw->pte is NULL. For PTE-mapped THP,
pvmw->pte is mapped. But for HugeTLB pages, pvmw->pte is not mapped and set
to the relevant page table entry. So in page_vma_mapped_walk_done(), we may
do pte_unmap() for HugeTLB pte which is not mapped. Fix this by checking
pvmw->page against PageHuge before trying to do pte_unmap().

Fixes: commit ("ace71a19cec5 mm: introduce page_vma_mapped_walk()")
Signed-off-by: Hongxiang Lou <louhongxiang@xxxxxxxxxx>
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
 include/linux/rmap.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 70085ca1a3fc..def5c62c93b3 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -213,7 +213,8 @@ struct page_vma_mapped_walk {
 
 static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw)
 {
-	if (pvmw->pte)
+	/* HugeTLB pte is set to the relevant page table entry without pte_mapped. */
+	if (pvmw->pte && !PageHuge(pvmw->page))
 		pte_unmap(pvmw->pte);
 	if (pvmw->ptl)
 		spin_unlock(pvmw->ptl);
-- 
2.19.1