Re: [PATCH v2 19/24] xtensa/cpu: Make sure cpu_die() doesn't return

Josh Poimboeuf
2023-02-14T20:19:20Z

On Tue, Feb 14, 2023 at 11:48:41AM -0800, Max Filippov wrote:
> On Tue, Feb 14, 2023 at 10:23 AM Josh Poimboeuf <jpoimboe@kernel.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.

Ah, I see. That sounds similar to what Xen does.

--
Josh