linux-kernel - Re: [PATCH 11/19] OpenRISC: Idle/Power management

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Date:	Mon, 20 Jun 2011 10:20:39 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Jonas Bonn <jonas@...thpole.se>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 11/19] OpenRISC: Idle/Power management

On Sunday 19 June 2011 13:43:37 Jonas Bonn wrote:
> +void cpu_idle(void)
> +{
> +        unsigned int cpu = smp_processor_id();
> +
> +        set_thread_flag(TIF_POLLING_NRFLAG);
> +
> +        /* endless idle loop with no priority at all */
> +        while (1) {
> +                tick_nohz_stop_sched_tick(1);
> +
> +                while (!need_resched()) {
> +                        check_pgt_cache();
> +                        rmb();
> +
> +/*                        if (cpu_is_offline(cpu))
> +                                play_dead();
> +*/
> +                       clear_thread_flag(TIF_POLLING_NRFLAG);
> +
> +                        local_irq_disable();
> +                        /* Don't trace irqs off for idle */
> +                        stop_critical_timings();
> +                       if (powersave != NULL )
> +                               powersave();
> +                       start_critical_timings();
> +                       local_irq_enable();
> +                       set_thread_flag(TIF_POLLING_NRFLAG);
> +                }
> +
> +                tick_nohz_restart_sched_tick();
> +                preempt_enable_no_resched();
> +                schedule();
> +                preempt_disable();
> +        }

Shouldn't you check need_resched() inside of local_irq_disable? Otherwise
you may get interrupted between the check at the start of the loop and
the irq_disable, which tries to wake up another process just before you go
to sleep indefinitely.

	Arnd
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