linux-kernel - Re: [PATCH 1/1] ntp: advertise correct TAI offset during leap second

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Date:	Sat, 05 May 2012 12:27:38 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Richard Cochran <richardcochran@...il.com>
CC:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/1] ntp: advertise correct TAI offset during leap second

On 05/05/2012 03:02 AM, Richard Cochran wrote:
> On Tue, May 01, 2012 at 08:16:05AM +0200, Richard Cochran wrote:
>> On Mon, Apr 30, 2012 at 12:48:22PM -0700, John Stultz wrote:
>>> On 04/27/2012 11:17 PM, Richard Cochran wrote:
>>>> Wait a minute. If user space manages this variable, then shouldn't the
>>>> kernel leave it alone?
>>> Right. That's why I'm asking. I actually haven't spent much time
>>> looking at how the tai value provided via adjtimex is handled, and I
>>> want to make sure its ok if we modify it from the kernel.
>> We *are* already modifying it in kernel, but at the wrong time.
>>
>> I don't know either what ntpd does, but I will find out.
>>
>> [ But if ntpd just uses adjtimex() to use the kernel as storage for
>>    variables, then that is really stupid. ]
> I took a look at ntp-4.2.6p5, and ntpd unconditionally sets the TAI
> offset using MOD_TAI when it thinks the offset has changed.
>
> But I think it won't hurt if the kernel changes the offset
> automatically, since ntpd will just try and set the same value again.
Assuming that it doesn't happen right before the tick that adjusts the 
leapsecond.  :)
But that's a pre-existing bug and not a reason to block your patch that 
improves things.

Thanks for the extra due-diligence here!

thanks
-john

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