btrfs: assert block group is locked in btrfs_use_block_group_size_class()

It's supposed to be called with the block group locked, in order to read
and set its size_class member, so assert it's locked.

Reviewed-by: Johannes Thumshirn <[email protected]>
Reviewed-by: Qu Wenruo <[email protected]>
Signed-off-by: Filipe Manana <[email protected]>
Reviewed-by: David Sterba <[email protected]>

Author: fdmanana

fs/btrfs/block-group.c

@@ -4755,6 +4755,7 @@ int btrfs_use_block_group_size_class(struct btrfs_block_group *bg,
 				     enum btrfs_block_group_size_class size_class,
 				     bool force_wrong_size_class)
 {
+	lockdep_assert_held(&bg->lock);
 	ASSERT(size_class != BTRFS_BG_SZ_NONE);
 
 	/* The new allocation is in the right size class, do nothing */