[PATCH] btrfs: Add comments on locking of several device-related fields

[Nikolay Borisov <nborisov@suse.com>]

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/volumes.h | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 3b97e8092ba7..514799362244 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -52,8 +52,8 @@ struct btrfs_io_geometry {
 #define BTRFS_DEV_STATE_FLUSH_SENT	(4)
 
 struct btrfs_device {
-	struct list_head dev_list;
-	struct list_head dev_alloc_list;
+	struct list_head dev_list; /* device_list_mutex */
+	struct list_head dev_alloc_list; /* chunk mutex */
 	struct list_head post_commit_list; /* chunk mutex */
 	struct btrfs_fs_devices *fs_devices;
 	struct btrfs_fs_info *fs_info;
@@ -238,9 +238,14 @@ struct btrfs_fs_devices {
 	 * this mutex lock.
 	 */
 	struct mutex device_list_mutex;
+
+	/* List of all devices, protected by device_list_mutex */
 	struct list_head devices;
 
-	/* devices not currently being allocated */
+	/*
+	 * Devices which can satisfy space allocation. Protected by
+	 * chunk_mutex
+	 */
 	struct list_head alloc_list;
 
 	struct btrfs_fs_devices *seed;
-- 
2.17.1