btrfs: document uuid_mutex uasge in read_chunk_tree

read_chunk_tree() calls read_one_dev(), but for seed device we have
to search the fs_uuids list, so we need the uuid_mutex. Add a comment
comment, so that we can improve this part.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index a382d53c560a..6eec1e3f9083 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6932,6 +6932,10 @@ int btrfs_read_chunk_tree(struct btrfs_fs_info *fs_info)
         if (!path)
                 return -ENOMEM;
 
+        /*
+         * uuid_mutex is needed only if we are mounting a sprout FS
+         * otherwise we don't need it.
+         */
         mutex_lock(&uuid_mutex);
         mutex_lock(&fs_info->chunk_mutex);