Use down_read_nested() to avoid the warning.

Reported-by: syzbot+49056626fe41e01f2ba7@syzkaller.appspotmail.com
Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
---
 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

On Thu, 21 Mar 2024 16:58:18 -0700 Lokesh Gidra <lokeshgidra@google.com> wrote:

> Use down_read_nested() to avoid the warning.
> 
> --- 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;

Thanks, I added 

Fixes: 867a43a34ff8a ("userfaultfd: use per-vma locks in userfaultfd operations")