[PATCH] Optimize sys_times for a single thread process

	BUG_ON(!list_empty(&p->ptrace_list) || !list_empty(&p->ptrace_children));

	__exit_signal(p);

	__exit_sighand(p);

	/*

	 * Note that the fastpath in sys_times depends on __exit_signal having

	 * updated the counters before a task is removed from the tasklist of

	 * the process by __unhash_process.

	 */

	__unhash_process(p);

	/*

	 */

	if (tbuf) {

		struct tms tmp;

		cputime_t utime, stime, cutime, cstime;

#ifdef CONFIG_SMP

		if (thread_group_empty(current)) {

			/*

			 * Single thread case without the use of any locks.

			 *

			 * We may race with release_task if two threads are

			 * executing. However, release task first adds up the

			 * counters (__exit_signal) before  removing the task

			 * from the process tasklist (__unhash_process).

			 * __exit_signal also acquires and releases the

			 * siglock which results in the proper memory ordering

			 * so that the list modifications are always visible

			 * after the counters have been updated.

			 *

			 * If the counters have been updated by the second thread

			 * but the thread has not yet been removed from the list

			 * then the other branch will be executing which will

			 * block on tasklist_lock until the exit handling of the

			 * other task is finished.

			 *

			 * This also implies that the sighand->siglock cannot

			 * be held by another processor. So we can also

			 * skip acquiring that lock.

			 */

			utime = cputime_add(current->signal->utime, current->utime);

			stime = cputime_add(current->signal->utime, current->stime);

			cutime = current->signal->cutime;

			cstime = current->signal->cstime;

		} else

#endif

		{

			/* Process with multiple threads */

			struct task_struct *tsk = current;

			struct task_struct *t;

		cputime_t utime, stime, cutime, cstime;

			read_lock(&tasklist_lock);

			utime = tsk->signal->utime;

			cstime = tsk->signal->cstime;

			spin_unlock_irq(&tsk->sighand->siglock);

			read_unlock(&tasklist_lock);

		}

		tmp.tms_utime = cputime_to_clock_t(utime);

		tmp.tms_stime = cputime_to_clock_t(stime);

		tmp.tms_cutime = cputime_to_clock_t(cutime);