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....@oracle.com>
---
v2: Use 'SINGLE_DEPTH_NESTING' to avoid magic number.
fs/btrfs/extent-tree.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 4607af3..68e9d25 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -7397,7 +7397,8 @@ btrfs_lock_cluster(struct btrfs_block_group_cache
*block_group,
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)
--
2.5.5
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