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

Josh Poimboeuf
2023-02-14T18:23:30Z

On Tue, Feb 14, 2023 at 08:55:32AM +0100, Philippe Mathieu-Daudé wrote:
> Hi Josh,
>
> On 14/2/23 08:05, Josh Poimboeuf wrote:
> > cpu_die() doesn't return. Make that more explicit with a BUG().
> >
> > BUG() is preferable to unreachable() because BUG() is a more explicit
> > failure mode and avoids undefined behavior like falling off the edge of
> > the function into whatever code happens to be next.
> >
> > Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
> > ---
> > arch/xtensa/kernel/smp.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/xtensa/kernel/smp.c b/arch/xtensa/kernel/smp.c
> > index 4dc109dd6214..7bad78495536 100644
> > --- a/arch/xtensa/kernel/smp.c
> > +++ b/arch/xtensa/kernel/smp.c
>
> 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.

Max/Chris?

--
Josh