linux-kernel - Re: [PATCH 08/14] hrtimer: Allow hrtimer::function() to free the timer

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Date:	Mon, 8 Jun 2015 10:06:07 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	Peter Zijlstra <peterz@...radead.org>, umgwanakikbuti@...il.com,
	mingo@...e.hu, ktkhai@...allels.com, rostedt@...dmis.org,
	juri.lelli@...il.com, pang.xunlei@...aro.org,
	wanpeng.li@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/14] hrtimer: Allow hrtimer::function() to free the
 timer

On Mon, 8 Jun 2015, Oleg Nesterov wrote:

> On 06/08, Oleg Nesterov wrote:
> >
> > And I simply can not understand the complication in hrtimer_active(),
> > please help!
> 
> Sorry for another off-topic email, but I don't even understand the
> usage of hrtimer_active().
> 
> Say, do_nanosleep()
> 
> 		hrtimer_start_expires(&t->timer, mode);
> 		if (!hrtimer_active(&t->timer))
> 			t->task = NULL;

That's gone in tip/timers/core. 

> OTOH. perf_cpu_hrtimer_restart() does
> 
> 	if (hrtimer_active(hr))
> 		return;
> 
> 	if (!hrtimer_callback_running(hr))
> 		__hrtimer_start_range_ns(...);
> 
> why it can't simply do
> 
> 	if (!hrtimer_active(hr)) // implies !hrtimer_callback_running()
> 		__hrtimer_start_range_ns(...);

That's fixed as well.

Thanks,

	tglx
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