[PATCH] filemap: replace pte_offset_map() with pte_offset_map_nolock()

[Peng Zhang <zhangpeng362@huawei.com>]

From: ZhangPeng <zhangpeng362@huawei.com>

The vmf->ptl in filemap_fault_recheck_pte_none() is still set from
handle_pte_fault(). But at the same time, we did a pte_unmap(vmf->pte).
After a pte_unmap(vmf->pte) unmap and rcu_read_unlock(), the page table
may be racily changed and vmf->ptl maybe fails to protect the actual
page table.
Fix this by replacing pte_offset_map() with pte_offset_map_nolock().

Fixes: 58f327f2ce80 ("filemap: avoid unnecessary major faults in filemap_fault()")
Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
---
 mm/filemap.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 31ab455c4537..222adac7c9c5 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3207,7 +3207,8 @@ static vm_fault_t filemap_fault_recheck_pte_none(struct vm_fault *vmf)
 	if (!(vmf->flags & FAULT_FLAG_ORIG_PTE_VALID))
 		return 0;
 
-	ptep = pte_offset_map(vmf->pmd, vmf->address);
+	ptep = pte_offset_map_nolock(vma->vm_mm, vmf->pmd, vmf->address,
+				     &vmf->ptl);
 	if (unlikely(!ptep))
 		return VM_FAULT_NOPAGE;
 
-- 
2.25.1