linux-kernel - Re: [REGRESSION] Xorg doesn't like 4e8b14526 "time: Improve sanity checking of timekeeping inputs"

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Message-ID: <20120901020252.GA6402@amos.fritz.box>
Date:	Sat, 1 Sep 2012 04:02:52 +0200
From:	Andreas Bombe <aeb@...ian.org>
To:	John Stultz <johnstul@...ibm.com>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [REGRESSION] Xorg doesn't like 4e8b14526 "time: Improve sanity
 checking of timekeeping inputs"

On Fri, Aug 31, 2012 at 10:43:42AM -0700, John Stultz wrote:
> On 08/30/2012 09:05 PM, Andreas Bombe wrote:
> >With that somewhat easy test I bisected it down to 4e8b14526 "time:
> >Improve sanity checking of timekeeping inputs". The latest Linus git
> >(155e36d40) with a revert of the bisected commit does not show the
> >problem.
> 
> Thanks so much for bisecting this down!
> I'm guessing X is passing crazy large timespecs into select (via
> WaitForSomething()) values that are catching on the ktime_t overflow
> check in timespec_valid(). Previously these would be clamped to
> KTIME_MAX (which basically is infinity) in the timer subsystem
> before.
> 
> So the issue is the patch in question is too strict in its
> validation. We want to be strict on things like timekeeping inputs,
> but for timers wait to infinity is still valid.
> 
> The attached (sorry not inline, on the road) patch should fix this,
> but could you verify it? (I'm running my testing concurrently)

I'm running it now and it's looking good. I did the video test again and
confirmed with strace that X was doing the giant timeout in select
again, but this time without any errors.

-- 
Andreas Bombe
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