void jbd2_journal_lock_updates(journal_t *journal)
{
	DEFINE_WAIT(wait);

	write_lock(&journal->j_state_lock);
	++journal->j_barrier_count;

	/* Wait until there are no running updates */
	while (1) {
		transaction_t *transaction = journal->j_running_transaction;

		if (!transaction)
			break;

		spin_lock(&transaction->t_handle_lock);
		prepare_to_wait(&journal->j_wait_updates, &wait,
				TASK_UNINTERRUPTIBLE);
		if (!atomic_read(&transaction->t_updates)) {
			spin_unlock(&transaction->t_handle_lock);
			finish_wait(&journal->j_wait_updates, &wait);
			break;
		}
		spin_unlock(&transaction->t_handle_lock);
		write_unlock(&journal->j_state_lock);
		schedule();
		finish_wait(&journal->j_wait_updates, &wait);
		write_lock(&journal->j_state_lock);
	}
	write_unlock(&journal->j_state_lock);

	/*
	 * We have now established a barrier against other normal updates, but
	 * we also need to barrier against other jbd2_journal_lock_updates() calls
	 * to make sure that we serialise special journal-locked operations
	 * too.
	 */
	mutex_lock(&journal->j_barrier);
}
void jbd2_journal_lock_updates(journal_t *journal)
{
	DEFINE_WAIT(wait);

	write_lock(&journal->j_state_lock);
	++journal->j_barrier_count;

	 
	while (1) {
		transaction_t *transaction = journal->j_running_transaction;

		if (!transaction)
			break;

		spin_lock(&transaction->t_handle_lock);
		prepare_to_wait(&journal->j_wait_updates, &wait,
				TASK_UNINTERRUPTIBLE);
		if (!atomic_read(&transaction->t_updates)) {
			spin_unlock(&transaction->t_handle_lock);
			finish_wait(&journal->j_wait_updates, &wait);
			break;
		}
		spin_unlock(&transaction->t_handle_lock);
		write_unlock(&journal->j_state_lock);
		schedule();
		finish_wait(&journal->j_wait_updates, &wait);
		write_lock(&journal->j_state_lock);
	}
	write_unlock(&journal->j_state_lock);

	 
	mutex_lock(&journal->j_barrier);
}