From: "Jakub Drnec" <jaydee@email.cz>
To: "linuxppc-dev" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: PROBLEM: monotonic clock going backwards on ppc64
Date: Fri, 01 Mar 2019 14:33:33 +0100 (CET) [thread overview]
Message-ID: <21Z.Zf5M.7zwRiKSx98z.1SUJIj@seznam.cz> (raw)
In-Reply-To: CA+7wUswyzc5SGjjb+WS4QpopyL0qoGYj0WF1jNaTfsC5ZsMpdw@mail.gmail.com
Hi,
>> Decreasing the realtime clock across the y2k38 threshold is one reliable way to reproduce.
>> Allegedly this can also happen just by running ntpd, I have not managed to reproduce that other
>> than booting with rtc at >2038 and then running ntp.
> Isn't it the expected behavior. Here is what I see for powermac:
>... gives us a time in the documented 1904..2040 year range. I decided not
This (or some related issue involving monotonic time going wonky) surfaced on a system running 4.5 kernel with sane clock values running ntpd. It may not be limited to setting the clock beyond 2038, that is just a convenient way to reproduce something visibly wrong.
If the "ntpd-related monotonic" issue is separate from what I reported, I did not find anything in the commit history that looks likely to have fixed that, so I think that is still a thing.
Another way of looking at the issue is that when you set the clock beyond 2038 (or the mystery ntpd thing happens), vdso and syscall versions of clock_gettime start reporting wildly different values for CLOCK_MONOTONIC. If someone manages to somehow interlace calls to those two assuming they are consistent, crazy bugs will ensue...
Regards,
Jakub
next prev parent reply other threads:[~2019-03-01 13:35 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-26 16:13 PROBLEM: monotonic clock going backwards on ppc64 Jakub Drnec
2019-02-28 6:48 ` Daniel Axtens
2019-02-28 7:04 ` Mathieu Malaterre
2019-02-28 11:17 ` Daniel Axtens
2019-03-01 13:33 ` Jakub Drnec [this message]
2019-03-01 13:24 ` Michael Ellerman
2019-03-01 23:59 ` Thomas Gleixner
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