[PATCH 4/5] btrfs: document what the spinlock unused_bgs_lock protects

[fdmanana@kernel.org]

From: Filipe Manana <fdmanana@suse.com>

Add some comments to struct btrfs_fs_info to explicitly document which
members are protected by the spinlock unused_bgs_lock. It is currently
used to protect two linked lists, the reclaim_bgs and unused_bgs lists.

So add an explicit comment on top of each list to mention its protected
by unused_bgs_lock, as well as comment on top of unused_bgs_lock to
mention the lists it protects.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/fs.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/btrfs/fs.h b/fs/btrfs/fs.h
index f8bb73d6ab68..b231a90e42cf 100644
--- a/fs/btrfs/fs.h
+++ b/fs/btrfs/fs.h
@@ -732,10 +732,13 @@ struct btrfs_fs_info {
 
 	/* Reclaim partially filled block groups in the background */
 	struct work_struct reclaim_bgs_work;
+	/* Protected by unused_bgs_lock. */
 	struct list_head reclaim_bgs;
 	int bg_reclaim_threshold;
 
+	/* Protects the lists unused_bgs and reclaim_bgs. */
 	spinlock_t unused_bgs_lock;
+	/* Protected by unused_bgs_lock. */
 	struct list_head unused_bgs;
 	struct mutex unused_bg_unpin_mutex;
 	/* Protect block groups that are going to be deleted */
-- 
2.40.1