linux-kernel - Re: [PATCH 2/4] nmi_backtrace: generate one-line reports for idle cpus

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Date:	Mon, 7 Mar 2016 12:05:00 -0500
From:	Chris Metcalf <cmetcalf@...lanox.com>
To:	Daniel Thompson <daniel.thompson@...aro.org>
CC:	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Andrew Morton <akpm@...l.org>,
	<linux-kernel@...r.kernel.org>, Aaron Tomlin <atomlin@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH 2/4] nmi_backtrace: generate one-line reports for idle
 cpus

On 03/07/2016 03:26 AM, Daniel Thompson wrote:
>> Chris Metcalf wrote:
>> +static DEFINE_PER_CPU(bool, cpu_idling);
>> +
>> +/* Was the cpu was in the low-level idle code when interrupted? */
>> +bool in_cpu_idle(void)
>> +{
>> +    return this_cpu_read(cpu_idling);
>
> I think we continue to need the code to identify a core that is 
> running an interrupt handler. Interrupts are not masked at the point 
> we set cpu_idling to false meaning we can easily be preempted before 
> we clear the flag.

Yes, good catch.  However, mooted by PeterZ wanting to keep any extra 
state-switching code out of the idle path.  See my reply to him for more 
on that.

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com