linux-kernel - timekeeping_adjust may set mult to 0

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Message-ID: <511912BB.2060602@sysgo.com>
Date:	Mon, 11 Feb 2013 16:48:11 +0100
From:	David Engraf <david.engraf@...go.com>
To:	John Stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	linux-kernel@...r.kernel.org
Subject: timekeeping_adjust may set mult to 0

Hi,

I have encountered a problem when a linux system uses a clocksource with 
mult = 1 and shift = 0 (clocksource cycle = nanoseconds). It may happen 
that the function timekeeping_adjust reduces the value of mult to 0 when 
error is lower than the interval [1].
As soon as timekeeper.mult is 0, ktime_get will no longer work because 
it uses timekeeping_get_ns which converts the cycle to nanoseconds with 
mult as 0 and the system clocksource returns always 0.

Best regards
David Engraf

[1] http://lxr.linux.no/linux+v3.0.62/kernel/time/timekeeping.c#L821
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