[PATCH 3.12 15/98] Btrfs: skip locking when searching commit root

[Jiri Slaby <jslaby@suse.cz>]

From: Wang Shilong <wangsl.fnst@cn.fujitsu.com>

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

===============

commit e84752d434b5cca0869e906e7b94d0531b25c6d3 upstream.

We won't change commit root, skip locking dance with commit root
when walking backrefs, this can speed up btrfs send operations.

Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 fs/btrfs/backref.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 5859a05f3a76..b7f40f2630f4 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -842,8 +842,10 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;
-	if (!trans)
+	if (!trans) {
 		path->search_commit_root = 1;
+		path->skip_locking = 1;
+	}
 
 	/*
 	 * grab both a lock on the path and a lock on the delayed ref head.
-- 
2.8.1