[PATCH 4.9 020/128] cgroup, blkcg: Prepare some symbols for module and !CONFIG_CGROUP usages

[Greg Kroah-Hartman]

From: Tejun Heo <tj@xxxxxxxxxx>

commit 9b0eb69b75bccada2d341d7e7ca342f0cb1c9a6a upstream.

btrfs is going to use css_put() and wbc helpers to improve cgroup
writeback support.  Add dummy css_get() definition and export wbc
helpers to prepare for module and !CONFIG_CGROUP builds.

[only backport the export of __inode_attach_wb for stable kernels - gregkh]

Reported-by: kbuild test robot <lkp@xxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/fs-writeback.c |    1 +
 1 file changed, 1 insertion(+)

--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -269,6 +269,7 @@ void __inode_attach_wb(struct inode *ino
 	if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
 		wb_put(wb);
 }
+EXPORT_SYMBOL_GPL(__inode_attach_wb);
 
 /**
  * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it