linux-kernel - Re: [PATCH] time, ntp: Do not update time

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Message-ID: <CALAqxLVm2JdDppCWvJOWasukcMPEokB93LOkRwKpoc_XEkEhBw@mail.gmail.com>
Date:	Wed, 11 Feb 2015 07:47:28 +0800
From:	John Stultz <john.stultz@...aro.org>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Miroslav Lichvar <mlichvar@...hat.com>
Subject: Re: [PATCH] time, ntp: Do not update time_state in middle of leap second

On Sun, Feb 8, 2015 at 2:29 AM, Prarit Bhargava <prarit@...hat.com> wrote:
> During leap second insertion testing it was noticed that a small window
> exists where the time_state could be reset such that
> time_state = TIME_OK, which then causes the leap second to not occur, or
> causes the entire leap second state machine to fail.

I think this description is fairly opaque, and probably needs the
specific example of the state change transitions that motivates this
patch.

> While this is highly unlikely to ever happen in the real world it is
> still something we should protect against, as breaking the state machine
> is obviously bad.

In this case it was a test-case bug where uninitialized data being
passed to adjtimex (when the test intended to only read the time
state) was causing an unexpected state change transition. So its not
immediately obvious that resetting the state machine when the root
called adjtimex is invalid, so it would be good to make this more
clear and explicit (ie: show the expected state transitions and the
command that caused the strange transition you saw).

Sorry for the slow response here, I've been on the fence as to if this
is the right thing or not, and have needed to get some time to stare
at this a bit more to see if I can convince myself its the right
thing, so improving the commit message might make it more obvious to
me and others. :)

thanks
-john
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