linux-kernel - Re: [PATCH 17/21] time: Fix a bug in timekeeping

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 3 Apr 2015 08:16:08 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Xunlei Pang <pang.xunlei@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 17/21] time: Fix a bug in timekeeping_suspend() with no
 persistent clock


* John Stultz <john.stultz@...aro.org> wrote:

> From: Xunlei Pang <pang.xunlei@...aro.org>
> 
> When there's no persistent clock, normally timekeeping_suspend_time
> should always be zero, but this can break in timekeeping_suspend().
> 
> At T1, there was a system suspend, so old_delta was assigned T1.
> After some time, one time adjustment happened, and xtime got the
> value of T1-dt(0s<dt<2s). Then, there comes another system suspend
> soon after this adjustment, obviously we will get a small negative
> delta_delta, resulting in a negative timekeeping_suspend_time.
> 
> This is problematic, when doing timekeeping_resume() if there is
> no nonstop clocksource for example, it will hit the else leg and
> inject the improper sleeptime which is the wrong logic.
> 
> So, we can solve this problem by only doing delta related code when
> the persistent clock is existent. Actually the code only makes sense
> for persistent clock cases.

What's the effect in practice of such negative delta_delta values? 
What kind of effects would users see from this?

Thanks,

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/