linux-kernel - Re: [PATCHv3 linux-next] hrtimer: Add notifier when clock_was

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Date:	Thu, 12 Sep 2013 16:43:37 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Herbert Xu <herbert@...dor.apana.org.au>
cc:	Fan Du <fan.du@...driver.com>,
	Steffen Klassert <steffen.klassert@...unet.com>,
	David Miller <davem@...emloft.net>,
	Daniel Borkmann <dborkman@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCHv3 linux-next] hrtimer: Add notifier when clock_was_set
 was called

On Thu, 12 Sep 2013, Herbert Xu wrote:
> On Thu, Sep 12, 2013 at 03:21:24PM +0200, Thomas Gleixner wrote:
> >
> > > (3): http://www.spinics.net/lists/netdev/msg245169.html
> > 
> > Thanks for the explanation so far.
> > 
> > What's still unclear to me is why these timeouts are bound to wall
> > time in the first place.
> > 
> > Is there any real reason why the key life time can't simply be
> > expressed in monotonic time, e.g. N seconds after creation or M
> > seconds after usage? Looking at the relevant RFCs I can't find any
> > requirement for binding the life time to wall time. 
> > 
> > A life time of 10 minutes does not change when the wall clock is
> > adjusted for whatever reasons. It's still 10 minutes and not some
> > random result of the wall clock adjustments. But I might be wrong as
> > usual :)
> 
> Well we started out with straight timers.  It was changed because
> people wanted IPsec SAs to expire after a suspect/resume which

Right suspend is the usual suspect :)

> AFAIK does not touch normal timers.
> 
> Of course, this brought with it a new set of problems when the
> system time is stepped which now cause SAs to expire even though
> they probably shouldn't.

Right. That's what I guessed. So your problem is that the timer_list
timers which are the proper mechanism for this (the life time has a 1
second granularity, so hrtimers are complete overkill) are not
expiring after a suspend/resume cycle.

So what about going back to timer_list timers and simply utilize
register_pm_notifier(), which will tell you that the system resumed?

Thanks,

	tglx

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