From mboxrd@z Thu Jan  1 00:00:00 1970
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
Subject: Re: Crashes in arm qemu emulations due to 'cpufreq: governor:
 Replace timers with utilization ...'
Date: Mon, 15 Feb 2016 19:07:00 +0000
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To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>, Peter Zijlstra <peterz@infradead.org>, Viresh Kumar <viresh.kumar@linaro.org>, "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>, "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-next@vger.kernel.org, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, Guenter Roeck <linux@roeck-us.net>

On Mon, Feb 15, 2016 at 07:54:26PM +0100, Rafael J. Wysocki wrote:
> On Mon, Feb 15, 2016 at 7:49 PM, Marc Zyngier <marc.zyngier@arm.com> wrote:
> > Given that OMAP3 is a UP system, there is zero chance that it has
> > registered the magic hook that delivers IPIs (its interrupt controller
> > is not even capable of doing so).
> >
> > I don't really know the context, but IPIs on a UP system seem at best odd.
> 
> That would explain it, thanks.
> 
> So it looks like we should always use irq_work_queue() on UP even if
> CONFIG_SMP is set, shouldn't we?

irq_work_queue_on() doesn't check whether 'cpu' is the CPU that we're
running on.  This is a problem where we want to be able to run a kernel
built for SMP on a UP system.

I guess the question is whether irq_work_queue_on() is buggy, or whether
our implementation of arch_send_call_function_single_ipi() is buggy.
Should arch_send_call_function_single_ipi() do something on UP systems,
if so what?

We don't have IPIs on UP systems, so we can't raise any interrupts.
So, should we call generic_smp_call_function_interrupt() directly
from it?

Some clues would be good...

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