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: Sun, 28 May 2017 10:54:34 +0200 [thread overview]
Message-ID: <20170528085434.7ygjfarqdgydzguy@gmail.com> (raw)
In-Reply-To: <CALAqxLWZpwS-L+jViRprXUAHzAw9TytDXDUY9y2_6DYK0k=YQg@mail.gmail.com>
* John Stultz <john.stultz@linaro.org> wrote:
> On Sat, May 27, 2017 at 12:38 AM, Ingo Molnar <mingo@kernel.org> wrote:
> >
> > * 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?
>
> Actually the first three are fixes (ARM64 still sees discontinuities
> until the vDSO is fixed), the last one is a cleanup.
Ok, please make it more apparent in the changelog of the third patch what user
observable mis-behavior is actually fixed by it: corrupted time, non-monotonic
time, or something else?
Thanks,
Ingo
next prev parent reply other threads:[~2017-05-28 8:54 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-27 3:33 [RFC][PATCH 0/4] Fixes for two recently found timekeeping bugs John Stultz
2017-05-27 3:33 ` [RFC][PATCH 1/4] time: Fix clock->read(clock) race around clocksource changes John Stultz
2017-05-27 7:31 ` Ingo Molnar
2017-05-27 3:33 ` [RFC][PATCH 2/4] time: Fix CLOCK_MONOTONIC_RAW sub-nanosecond accounting John Stultz
2017-05-27 7:36 ` Ingo Molnar
2017-05-30 18:42 ` Daniel Mentz
2017-05-27 3:33 ` [RFC][PATCH 3/4] arm64: vdso: Fix nsec handling for CLOCK_MONOTONIC_RAW John Stultz
2017-05-30 9:38 ` Will Deacon
2017-05-27 3:33 ` [RFC][PATCH 4/4] time: Clean up CLOCK_MONOTONIC_RAW time handling John Stultz
2017-08-25 13:40 ` Chris Wilson
2017-08-25 18:55 ` John Stultz
2017-08-25 21:16 ` John Stultz
2017-08-25 22:57 ` [RFC][PATCH] time: Fix ktime_get_raw() issues caused by incorrect base accumulation John Stultz
2017-08-26 10:20 ` Chris Wilson
2017-08-26 14:10 ` [tip:timers/urgent] time: Fix ktime_get_raw() " tip-bot for John Stultz
2017-05-27 7:38 ` [RFC][PATCH 0/4] Fixes for two recently found timekeeping bugs Ingo Molnar
2017-05-27 16:16 ` John Stultz
2017-05-28 8:54 ` Ingo Molnar [this message]
[not found] ` <CAE2F3rBuOJqLs5Cu7A9wEruZj1Vmnpy6qAYW=U9FVAOEP73pdg@mail.gmail.com>
2017-05-31 0:11 ` Daniel Mentz
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