linux-kernel - Re: [RFC][PATCH 0/4] Fixes for two recently found timekeeping bugs

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Date:   Sat, 27 May 2017 09:38:36 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Miroslav Lichvar <mlichvar@...hat.com>,
        Richard Cochran <richardcochran@...il.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Stephen Boyd <stephen.boyd@...aro.org>,
        Daniel Mentz <danielmentz@...gle.com>
Subject: Re: [RFC][PATCH 0/4] Fixes for two recently found timekeeping bugs


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

> As part of the Linaro Linux Kernel Functional Test (LKFT)
> effort, test failures from kselftest/timer's
> inconsistency-check were reported connected to
> CLOCK_MONOTONIC_RAW, on the HiKey platform.
> 
> Digging in I found that an old issue with how sub-ns accounting
> is handled with the RAW time which was fixed long ago with the
> CLOCK_MONOTONIC/REALTIME ids, but missed with RAW time, was
> present.
> 
> Additionally, running further tests, I uncovered an issue with
> how the clocksource read function is handled when clocksources
> are changed, which can cause crashes.
> 
> Both of these issues have not been uncovered in x86 based
> testing due to x86 not using vDSO to accelerate
> CLOCK_MONOTONIC_RAW, combined with the HiKey's arch_timer
> clocksource being fast to access but incrementing slowly enough
> to get multiple reads using the same counter value (which helps
> uncover time handing issues), along with the fact that none of
> the x86 clocksources making use of the clocksource argument
> passed to the read function.
> 
> This patchset addresses these two issues. 

AFAICS only the first two patches are fixes, the other two patches are 
cleanups/simplifications that resulted out of the debugging effort, right?

Thanks,

	Ingo