linux-kernel - Re: [PATCH v2 19/24] xtensa/cpu: Make sure cpu

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Message-ID: <CAMo8BfLzV0Oe_i-QrMzE-BE028s6GNvOd827N5+tteELidjpvA@mail.gmail.com>
Date:   Tue, 14 Feb 2023 11:48:41 -0800
From:   Max Filippov <jcmvbkbc@...il.com>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     Philippe Mathieu-Daudé <philmd@...aro.org>,
        linux-kernel@...r.kernel.org, jgross@...e.com,
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Subject: Re: [PATCH v2 19/24] xtensa/cpu: Make sure cpu_die() doesn't return

On Tue, Feb 14, 2023 at 10:23 AM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
> On Tue, Feb 14, 2023 at 08:55:32AM +0100, Philippe Mathieu-Daudé wrote:
> > Can you update the documentation along? Currently we have:
> >
> >   /*
> >    * Called from the idle thread for the CPU which has been shutdown.
> >    *
> >    * Note that we disable IRQs here, but do not re-enable them
> >    * before returning to the caller. This is also the behaviour
> >    * of the other hotplug-cpu capable cores, so presumably coming
> >    * out of idle fixes this.
> >    */
>
> void __ref cpu_die(void)
> {
>         idle_task_exit();
>         local_irq_disable();
>         __asm__ __volatile__(
>                         "       movi    a2, cpu_restart\n"
>                         "       jx      a2\n");
>
>         BUG();
> }
>
> Hm, not only is the comment wrong, but it seems to be branching to
> cpu_restart?  That doesn't seem right at all.

Perhaps the name is a bit misleading. The CPU that enters 'cpu_restart'
loops there until a call to 'boot_secondary' releases it, after which it goes
to '_startup'. So it is a restart, but not immediate.

-- 
Thanks.
-- Max