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

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Date:	Tue, 9 Jun 2015 23:39:35 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	umgwanakikbuti@...il.com, mingo@...e.hu, ktkhai@...allels.com,
	rostedt@...dmis.org, tglx@...utronix.de, 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

Damn,

On 06/09, Oleg Nesterov wrote:
>
> Yes, we only have this 2nd write_seqcount_begin/end if the timer re-
> arms itself, but otherwise we do not race. If another thread does
> hrtime_start() in between we can pretend that hrtimer_active() hits
> the "inactive".
  ^^^^^^^^^^^^^^^

I meant,

	hits the "inactive" window we can't avoid. Even if another
	thread does this _before_ __run_hrtimer() clears ->running,
	we can't distinguish from the case when it does this right
	_after_ the timer becomes "inactive".

Oleg.

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