[PATCH] userfaultfd: fix deadlock warning when locking src and dst VMAs

[Lokesh Gidra]

Use down_read_nested() to avoid the warning.

Reported-by: syzbot+49056626fe41e01f2ba7@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
---
 mm/userfaultfd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 712160cd41ec..3c3539c573e7 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1444,7 +1444,8 @@ static int uffd_move_lock(struct mm_struct *mm,
 		 */
 		down_read(&(*dst_vmap)->vm_lock->lock);
 		if (*dst_vmap != *src_vmap)
-			down_read(&(*src_vmap)->vm_lock->lock);
+			down_read_nested(&(*src_vmap)->vm_lock->lock,
+					 SINGLE_DEPTH_NESTING);
 	}
 	mmap_read_unlock(mm);
 	return err;
-- 
2.44.0.396.g6e790dbe36-goog