btrfs: simplify error handling of clean_pinned_extents()

At clean_pinned_extents(), whether we end up returning success or failure,
we pretty much have to do the same things:

1) unlock unused_bg_unpin_mutex
2) decrement reference count on the previous transaction

We also call btrfs_dec_block_group_ro() in case of failure, but that is
better done in its caller, btrfs_delete_unused_bgs(), since its the
caller that calls inc_block_group_ro(), so it should be responsible for
the decrement operation, as it is in case any of the other functions it
calls fail.

So move the call to btrfs_dec_block_group_ro() from clean_pinned_extents()
into  btrfs_delete_unused_bgs() and unify the error and success return
paths for clean_pinned_extents(), reducing duplicated code and making it
simpler.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-group.c

@@ -1284,25 +1284,17 @@ static bool clean_pinned_extents(struct btrfs_trans_handle *trans,
 		ret = clear_extent_bits(&prev_trans->pinned_extents, start, end,
 					EXTENT_DIRTY);
 		if (ret)
-			goto err;
+			goto out;
 	}
 
 	ret = clear_extent_bits(&trans->transaction->pinned_extents, start, end,
 				EXTENT_DIRTY);
-	if (ret)
-		goto err;
+out:
 	mutex_unlock(&fs_info->unused_bg_unpin_mutex);
 	if (prev_trans)
 		btrfs_put_transaction(prev_trans);
 
-	return true;
-
-err:
-	mutex_unlock(&fs_info->unused_bg_unpin_mutex);
-	if (prev_trans)
-		btrfs_put_transaction(prev_trans);
-	btrfs_dec_block_group_ro(bg);
-	return false;
+	return ret == 0;
 }
 
 /*
@@ -1400,8 +1392,10 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
 		 * We could have pending pinned extents for this block group,
 		 * just delete them, we don't care about them anymore.
 		 */
-		if (!clean_pinned_extents(trans, block_group))
+		if (!clean_pinned_extents(trans, block_group)) {
+			btrfs_dec_block_group_ro(block_group);
 			goto end_trans;
+		}
 
 		/*
 		 * At this point, the block_group is read only and should fail