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Date: Mon, 21 May 2018 21:03:14 +0200
From: Greg KH <gregkh@linuxfoundation.org>
To: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Cc: Ben Hutchings <ben.hutchings@codethink.co.uk>,
        Chris Paterson <Chris.Paterson2@renesas.com>,
        Biju Das <biju.das@bp.renesas.com>, stable@vger.kernel.org
Subject: Re: [PATCH] time: Fix CLOCK_MONOTONIC_RAW sub-nanosecond accounting
Message-ID: <20180521190314.GA9667@kroah.com>
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On Mon, May 21, 2018 at 06:57:26PM +0100, Fabrizio Castro wrote:
> From: John Stultz <john.stultz@linaro.org>
> 
> commit 3d88d56c5873f6eebe23e05c3da701960146b801 upstream.
> 
> Due to how the MONOTONIC_RAW accumulation logic was handled,
> there is the potential for a 1ns discontinuity when we do
> accumulations. This small discontinuity has for the most part
> gone un-noticed, but since ARM64 enabled CLOCK_MONOTONIC_RAW
> in their vDSO clock_gettime implementation, we've seen failures
> with the inconsistency-check test in kselftest.
> 
> This patch addresses the issue by using the same sub-ns
> accumulation handling that CLOCK_MONOTONIC uses, which avoids
> the issue for in-kernel users.
> 
> Since the ARM64 vDSO implementation has its own clock_gettime
> calculation logic, this patch reduces the frequency of errors,
> but failures are still seen. The ARM64 vDSO will need to be
> updated to include the sub-nanosecond xtime_nsec values in its
> calculation for this issue to be completely fixed.
> 
> Signed-off-by: John Stultz <john.stultz@linaro.org>
> Tested-by: Daniel Mentz <danielmentz@google.com>
> Cc: Prarit Bhargava <prarit@redhat.com>
> Cc: Kevin Brodsky <kevin.brodsky@arm.com>
> Cc: Richard Cochran <richardcochran@gmail.com>
> Cc: Stephen Boyd <stephen.boyd@linaro.org>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: "stable #4 . 8+" <stable@vger.kernel.org>
> Cc: Miroslav Lichvar <mlichvar@redhat.com>
> Link: http://lkml.kernel.org/r/1496965462-20003-3-git-send-email-john.stultz@linaro.org
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> [fabrizio: cherry-pick to 4.4. Kept cycle_t type for function
> logarithmic_accumulation local variable "interval". Dropped
> casting of "interval" variable]
> Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
> Signed-off-by: Biju Das <biju.das@bp.renesas.com>
> ---
> Hello Greg,
> 
> we noticed tools/testing/selftests/timers/clocksource-switch.c
> was failing for us, this patch fixes the cause of the failure.
> Are you happy to take this patch?

For what kernel tree(s)?

And why did you not cc: the developers and maintainer of this subsystem?

thanks,

greg k-h