Btrfs: make get_caching_control unconditionally return the ctl

This was written when we didn't do a caching control for the fast free space
cache loading.  However we started doing that a long time ago, and there is
still a small window of time that we could be caching the block group the fast
way, so if there is a caching_ctl at all on the block group just return it, the
callers all wait properly for what they want.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/extent-tree.c

@@ -315,12 +315,6 @@ get_caching_control(struct btrfs_block_group_cache *cache)
 	struct btrfs_caching_control *ctl;
 
 	spin_lock(&cache->lock);
-	if (cache->cached != BTRFS_CACHE_STARTED) {
-		spin_unlock(&cache->lock);
-		return NULL;
-	}
-
-	/* We're loading it the fast way, so we don't have a caching_ctl. */
 	if (!cache->caching_ctl) {
 		spin_unlock(&cache->lock);
 		return NULL;
@@ -594,13 +588,15 @@ static int cache_block_group(struct btrfs_block_group_cache *cache,
 	spin_unlock(&cache->lock);
 
 	if (fs_info->mount_opt & BTRFS_MOUNT_SPACE_CACHE) {
+		mutex_lock(&caching_ctl->mutex);
 		ret = load_free_space_cache(fs_info, cache);
 
 		spin_lock(&cache->lock);
 		if (ret == 1) {
 			cache->caching_ctl = NULL;
 			cache->cached = BTRFS_CACHE_FINISHED;
 			cache->last_byte_to_unpin = (u64)-1;
+			caching_ctl->progress = (u64)-1;
 		} else {
 			if (load_cache_only) {
 				cache->caching_ctl = NULL;
@@ -611,6 +607,8 @@ static int cache_block_group(struct btrfs_block_group_cache *cache,
 			}
 		}
 		spin_unlock(&cache->lock);
+		mutex_unlock(&caching_ctl->mutex);
+
 		wake_up(&caching_ctl->wait);
 		if (ret == 1) {
 			put_caching_control(caching_ctl);