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

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Message-ID: <alpine.DEB.2.11.1510091238071.6097@nanos>
Date:	Fri, 9 Oct 2015 12:38:32 +0200 (CEST)
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 Fri, 9 Oct 2015, Miroslav Lichvar wrote:
> On Fri, Oct 09, 2015 at 10:46:16AM +0100, Thomas Gleixner wrote:
> > On Thu, 8 Oct 2015, Miroslav Lichvar wrote:
> > > 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.
> 
> I think vast majority of them won't fall. It doesn't prevent all
> problems, but at least the userspace agrees with kernel on what the
> current time it is, that looks to me like the most difficult one to
> fix in applications.
> 
> > We need to fix all of it, no matter what.
> 
> Yeah, that would be nice, but I don't think it's realistic.
> 
> Do you feel the same about preventing the time from reaching
> KTIME_MAX?

That's going to happen in ~500 years from now.

Thanks,

	tglx
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