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

From: Ingo Molnar <mingo@kernel.org>
To: John Stultz <john.stultz@linaro.org>
Cc: lkml <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Miroslav Lichvar <mlichvar@redhat.com>,
	Richard Cochran <richardcochran@gmail.com>,
	Prarit Bhargava <prarit@redhat.com>,
	Stephen Boyd <stephen.boyd@linaro.org>,
	Daniel Mentz <danielmentz@google.com>
Subject: Re: [RFC][PATCH 0/4] Fixes for two recently found timekeeping bugs
Date: Sat, 27 May 2017 09:38:36 +0200	[thread overview]
Message-ID: <20170527073836.7rxbn5kdf5c536q5@gmail.com> (raw)
In-Reply-To: <1495856035-6622-1-git-send-email-john.stultz@linaro.org>

* John Stultz <john.stultz@linaro.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