linux-kernel - Re: [patch 15/36] Hexagon: Add init

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Date:	Wed, 17 Aug 2011 21:45:10 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Richard Kuo <rkuo@...eaurora.org>
Cc:	linux-kernel@...r.kernel.org, linux-hexagon@...r.kernel.org
Subject: Re: [patch 15/36] Hexagon: Add init_task and process functions

On Wednesday 17 August 2011 11:35:12 Richard Kuo wrote:
> +/*
> + *  Spin, or better still, do a hardware or VM wait instruction
> + *  If hardware or VM offer wait termination even though interrupts
> + *  are disabled.
> + */
> +static void default_idle(void)
> +{
> +       __vmwait();
> +}
> +
> +void (*idle_sleep)(void) = default_idle;
> +
> +void cpu_idle(void)
> +{
> +       while (1) {
> +               tick_nohz_stop_sched_tick(1);
> +               while (!need_resched())
> +                       idle_sleep();
> +               tick_nohz_restart_sched_tick();
> +               schedule();
> +       }
> +}

This looks like you have the classic going to sleep race in here:

You need to disable hardware interrupts before checking need_resched(),
otherwise an interrupt might hit just after you have checked it and
before you call __vmwait(). The definition of the __vmwait call
must atomically reenable interrupts and suspend the CPU.

	Arnd
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