[PATCH 4.9 079/105] Btrfs: use down_read_nested to make lockdep silent

From: Greg Kroah-Hartman
Date: Fri Aug 04 2017 - 19:26:30 EST


4.9-stable review patch. If anyone has any objections, please let me know.

------------------

From: Liu Bo <bo.li.liu@xxxxxxxxxx>


[ Upstream commit e321f8a801d7b4c40da8005257b05b9c2b51b072 ]

If @block_group is not @used_bg, it'll try to get @used_bg's lock without
droping @block_group 's lock and lockdep has throwed a scary deadlock warning
about it.
Fix it by using down_read_nested.

Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/extent-tree.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -7401,7 +7401,8 @@ btrfs_lock_cluster(struct btrfs_block_gr

spin_unlock(&cluster->refill_lock);

- down_read(&used_bg->data_rwsem);
+ /* We should only have one-level nested. */
+ down_read_nested(&used_bg->data_rwsem, SINGLE_DEPTH_NESTING);

spin_lock(&cluster->refill_lock);
if (used_bg == cluster->block_group)