linux-kernel - Re: [PATCH] timekeeping: Limit system time to prevent 32-bit time

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Message-ID: <alpine.DEB.2.11.1510091032100.6097@nanos>
Date:	Fri, 9 Oct 2015 10:46:16 +0100 (IST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Miroslav Lichvar <mlichvar@...hat.com>
cc:	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	y2038@...ts.linaro.org, John Stultz <john.stultz@...aro.org>,
	Prarit Bhargava <prarit@...hat.com>,
	Richard Cochran <richardcochran@...il.com>
Subject: Re: [PATCH] timekeeping: Limit system time to prevent 32-bit time_t
 overflow

On Thu, 8 Oct 2015, Miroslav Lichvar wrote:
> On Thu, Oct 08, 2015 at 10:52:05AM +0200, Arnd Bergmann wrote:
> > On Thursday 08 October 2015 08:23:44 Miroslav Lichvar wrote:
> > > The difference is that with the one-week step the kernel and userspace
> > > still agree on the current time and it is always valid from the kernel
> > > point of view, absolute timers can be set, etc.
> > 
> > Ok, I can see that as an improvement, but it still seems to give
> > a false sense of safety, and I feel we really should not have any code
> > rely on this behavior.
> 
> Applications are not allowed to rely on system time being sane?
> To me the current behavior looks like the kernel is throwing the
> applications off a cliff, while it's the only thing that can fly :).

As Arnd said, you are creating a wrong sense of safety. They fall off
the cliff with your changes as well. The fall is just different. Think
about timeouts, user space overflows of time_t etc.

We need to fix all of it, no matter what.

Thanks,

	tglx




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