linux-kernel - Re: [PATCH 1/2] time: Fix a bug in timekeeping

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Date:	Tue, 24 Mar 2015 14:23:17 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Xunlei Pang <xlpang@....com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	"rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Arnd Bergmann <arnd.bergmann@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Xunlei Pang <pang.xunlei@...aro.org>
Subject: Re: [PATCH 1/2] time: Fix a bug in timekeeping_suspend() with no
 persistent clock

On Wed, Mar 18, 2015 at 7:42 PM, Xunlei Pang <xlpang@....com> wrote:
> From: Xunlei Pang <pang.xunlei@...aro.org>
>
> When there's no persistent clock, normally timekeeping_suspend_time
> should always be zero, but this can break in timekeeping_suspend().
>
> At T1, there was a system suspend, so old_delta was assigned T1.
> After some time, one time adjustment happened, and xtime got the
> value of T1-dt(0s<dt<2s). Then, there comes another system suspend
> soon after this adjustment, obviously we will get a small negative
> delta_delta, resulting in a negative timekeeping_suspend_time.
>
> This is problematic, when doing timekeeping_resume() if there is
> no nonstop clocksource for example, it will hit the else leg and
> inject the improper sleeptime which is the wrong logic.
>
> So, we can solve this problem by only doing delta related code when
> the persistent clock is existent. Actually the code only makes sense
> for persistent clock cases.
>
> Signed-off-by: Xunlei Pang <pang.xunlei@...aro.org>

Thanks for resending this with the changes, Xunlei. I've queued these
two patches for 4.1

thanks
-john
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