Btrfs: cleanup the code of used_block_group in find_free_extent()

used_block_group is just used for the space cluster which doesn't
belong to the current block group, the other place needn't use it.
Or the logic of code seems unclear.
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/extent-tree.c

@@ -6159,7 +6159,6 @@ static noinline int find_free_extent(struct btrfs_root *orig_root,
 	struct btrfs_root *root = orig_root->fs_info->extent_root;
 	struct btrfs_free_cluster *last_ptr = NULL;
 	struct btrfs_block_group_cache *block_group = NULL;
-	struct btrfs_block_group_cache *used_block_group;
 	u64 search_start = 0;
 	u64 max_extent_size = 0;
 	int empty_cluster = 2 * 1024 * 1024;
@@ -6220,7 +6219,6 @@ static noinline int find_free_extent(struct btrfs_root *orig_root,
 	if (search_start == hint_byte) {
 		block_group = btrfs_lookup_block_group(root->fs_info,
 						       search_start);
-		used_block_group = block_group;
 		/*
 		 * we don't want to use the block group if it doesn't match our
 		 * allocation bits, or if its not cached.
@@ -6257,7 +6255,6 @@ static noinline int find_free_extent(struct btrfs_root *orig_root,
 		u64 offset;
 		int cached;
 
-		used_block_group = block_group;
 		btrfs_get_block_group(block_group);
 		search_start = block_group->key.objectid;
 
@@ -6300,6 +6297,7 @@ static noinline int find_free_extent(struct btrfs_root *orig_root,
 		 * lets look there
 		 */
 		if (last_ptr) {
+			struct btrfs_block_group_cache *used_block_group;
 			unsigned long aligned_cluster;
 			/*
 			 * the refill lock keeps out other
@@ -6310,10 +6308,8 @@ static noinline int find_free_extent(struct btrfs_root *orig_root,
 			if (used_block_group != block_group &&
 			    (!used_block_group ||
 			     used_block_group->ro ||
-			     !block_group_bits(used_block_group, flags))) {
-				used_block_group = block_group;
+			     !block_group_bits(used_block_group, flags)))
 				goto refill_cluster;
-			}
 
 			if (used_block_group != block_group)
 				btrfs_get_block_group(used_block_group);
@@ -6328,16 +6324,17 @@ static noinline int find_free_extent(struct btrfs_root *orig_root,
 				spin_unlock(&last_ptr->refill_lock);
 				trace_btrfs_reserve_extent_cluster(root,
 					block_group, search_start, num_bytes);
+				if (used_block_group != block_group) {
+					btrfs_put_block_group(block_group);
+					block_group = used_block_group;
+				}
 				goto checks;
 			}
 
 			WARN_ON(last_ptr->block_group != used_block_group);
-			if (used_block_group != block_group) {
+			if (used_block_group != block_group)
 				btrfs_put_block_group(used_block_group);
-				used_block_group = block_group;
-			}
 refill_cluster:
-			BUG_ON(used_block_group != block_group);
 			/* If we are on LOOP_NO_EMPTY_SIZE, we can't
 			 * set up a new clusters, so lets just skip it
 			 * and let the allocator find whatever block
@@ -6456,25 +6453,25 @@ static noinline int find_free_extent(struct btrfs_root *orig_root,
 			goto loop;
 		}
 checks:
-		search_start = stripe_align(root, used_block_group,
+		search_start = stripe_align(root, block_group,
 					    offset, num_bytes);
 
 		/* move on to the next group */
 		if (search_start + num_bytes >
-		    used_block_group->key.objectid + used_block_group->key.offset) {
-			btrfs_add_free_space(used_block_group, offset, num_bytes);
+		    block_group->key.objectid + block_group->key.offset) {
+			btrfs_add_free_space(block_group, offset, num_bytes);
 			goto loop;
 		}
 
 		if (offset < search_start)
-			btrfs_add_free_space(used_block_group, offset,
+			btrfs_add_free_space(block_group, offset,
 					     search_start - offset);
 		BUG_ON(offset > search_start);
 
-		ret = btrfs_update_reserved_bytes(used_block_group, num_bytes,
+		ret = btrfs_update_reserved_bytes(block_group, num_bytes,
 						  alloc_type);
 		if (ret == -EAGAIN) {
-			btrfs_add_free_space(used_block_group, offset, num_bytes);
+			btrfs_add_free_space(block_group, offset, num_bytes);
 			goto loop;
 		}
 
@@ -6484,16 +6481,12 @@ static noinline int find_free_extent(struct btrfs_root *orig_root,
 
 		trace_btrfs_reserve_extent(orig_root, block_group,
 					   search_start, num_bytes);
-		if (used_block_group != block_group)
-			btrfs_put_block_group(used_block_group);
 		btrfs_put_block_group(block_group);
 		break;
 loop:
 		failed_cluster_refill = false;
 		failed_alloc = false;
 		BUG_ON(index != get_block_group_index(block_group));
-		if (used_block_group != block_group)
-			btrfs_put_block_group(used_block_group);
 		btrfs_put_block_group(block_group);
 	}
 	up_read(&space_info->groups_sem);