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

	jbd2_might_wait_for_commit(journal);

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

	/* Wait until there are no reserved handles */
	if (atomic_read(&journal->j_reserved_credits)) {
		write_unlock(&journal->j_state_lock);
		wait_event(journal->j_wait_reserved,
			   atomic_read(&journal->j_reserved_credits) == 0);
		write_lock(&journal->j_state_lock);
	}

	/* Wait until there are no running t_updates */
	jbd2_journal_wait_updates(journal);

	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);
}
Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.