linux-kernel - Re: [PATCH 2/2] tick: Make sure tick timer is active when bypassing reprogramming

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Date:   Thu, 20 Apr 2017 21:40:12 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Frederic Weisbecker <fweisbec@...il.com>
cc:     Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...hat.com>,
        James Hartsock <hartsjc@...hat.com>, stable@...r.kernel.org,
        Tim Wright <tim@...bash.co.uk>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH 2/2] tick: Make sure tick timer is active when bypassing
 reprogramming

On Thu, 20 Apr 2017, Frederic Weisbecker wrote:
> On Thu, Apr 20, 2017 at 07:56:22PM +0200, Thomas Gleixner wrote:
> > >  	/* Skip reprogram of event if its not changed */
> > > -	if (ts->tick_stopped && (expires == ts->next_tick))
> > > +	if (ts->tick_stopped && (expires == ts->next_tick)) {
> > > +		WARN_ON_ONCE(dev->next_event > ts->next_tick);
> > 
> > What about handling it proper ? dev->next_event might be KTIME_MAX,
> > i.e. no more event for the next 500+ years.
> 
> I thought I handled this case, what I'm I missing?

	if (ts->tick_stopped && (expires == ts->next_tick)) {
		WARN_ON_ONCE(dev->next_event > ts->next_tick);
		goto out;
	}

IOW, the WARN_ON yells in dmesg, but despite seing the wreckage it just
leaves it and goes out doing nothing.

Why can't you just do

	if (ts->tick_stopped && (expires == ts->next_tick)) {
	   	if (dev->next_event > ts->next_tick)) {
			WARN_ONCE();
			do_something_sensible();
		}		
		goto out;
	}

Hmm?

	tglx