Date: Tue, 9 Jun 2015 23:39:35 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: umgwanakikbuti@gmail.com, mingo@elte.hu, ktkhai@parallels.com,
        rostedt@goodmis.org, tglx@linutronix.de, juri.lelli@gmail.com,
        pang.xunlei@linaro.org, wanpeng.li@linux.intel.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 08/14] hrtimer: Allow hrtimer::function() to free the
	timer
Message-ID: <20150609213935.GA14225@redhat.com>
References: <20150605084836.364306429@infradead.org> <20150605085205.723058588@infradead.org> <20150607223317.GA5193@redhat.com> <20150608091417.GM19282@twins.programming.kicks-ass.net> <20150608124234.GW18673@twins.programming.kicks-ass.net> <20150609213318.GA12436@redhat.com>
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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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