From: Andrey Vagin <avagin@virtuozzo.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
Dmitry Safonov <dima@arista.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Dmitry Safonov <0x7f454c46@gmail.com>,
Adrian Reber <adrian@lisas.de>, Andy Lutomirski <luto@kernel.org>,
Christian Brauner <christian.brauner@ubuntu.com>,
Cyrill Gorcunov <gorcunov@openvz.org>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
Jeff Dike <jdike@addtoit.com>, Oleg Nesterov <oleg@redhat.com>,
Pavel Emelianov <xemul@virtuozzo.com>,
Shuah Khan <shuah@kernel.org>,
"containers@lists.linux-foundation.org"
<containers@lists.linux-foundation.org>,
"criu@openvz.org" <criu@openvz.org>,
"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
"linux-kselftest@vger.kernel.org"
<linux-kselftest@vger.kernel.org>
Subject: Re: [RFC 00/20] ns: Introduce Time Namespace
Date: Mon, 1 Oct 2018 23:20:47 +0000 [thread overview]
Message-ID: <20181001232033.GA31324@outlook.office365.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1809272335430.8118@nanos.tec.linutronix.de>
On Thu, Sep 27, 2018 at 11:41:49PM +0200, Thomas Gleixner wrote:
> On Thu, 27 Sep 2018, Thomas Gleixner wrote:
> > Add time skew via NTP/PTP into the picture and you might have to adjust
> > timers as well, because you need to guarantee that they are not expiring
> > early.
> >
> > I haven't looked through Dimitry's patches yet, but I don't see how this
> > can work at all without introducing subtle issues all over the place.
>
> And just a quick scan tells me that this is broken. Timers will expire
> early or late. The latter is acceptible to some extent, but larger delays
> might come with surprise. Expiring early is an absolute nono.
Do you mean that we have to adjust all timers after changing offset for
CLOCK_MONOTONIC or CLOCK_BOOTTIME? Our idea is that offsets for
monotonic and boot times will be set immediately after creating a time
namespace before using any timers.
It is interesting to think what a use-case for changing these offsets
after creating timers. It may be useful for testing needs. A user sets a
timer in an hour and then change a clock offset forward and check that a
test application handles the timer properly.
>
> Thanks,
>
> tglx
>
next prev parent reply other threads:[~2018-10-01 23:20 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-19 20:50 Dmitry Safonov
2018-09-19 20:50 ` [RFC 01/20] " Dmitry Safonov
2018-09-28 18:20 ` Laurent Vivier
2018-09-19 20:50 ` [RFC 02/20] timens: Add timens_offsets Dmitry Safonov
2018-09-20 18:45 ` Cyrill Gorcunov
2018-09-20 22:14 ` Cyrill Gorcunov
2018-09-19 20:50 ` [RFC 03/20] timens: Introduce CLOCK_MONOTONIC offsets Dmitry Safonov
2018-09-19 20:50 ` [RFC 04/20] timens: Introduce CLOCK_BOOTTIME offset Dmitry Safonov
2018-09-30 3:18 ` [LKP] [timens] 3cc8de9dcb: RIP:posix_get_boottime kernel test robot
2018-09-19 20:50 ` [RFC 05/20] timerfd/timens: Take into account ns clock offsets Dmitry Safonov
2018-09-19 20:50 ` [RFC 06/20] kernel: Take into account timens clock offsets in clock_nanosleep Dmitry Safonov
2018-09-19 20:50 ` [RFC 07/20] timens: Shift /proc/uptime Dmitry Safonov
2018-09-19 20:50 ` [RFC 08/20] x86/vdso: Restrict splitting vvar vma Dmitry Safonov
2018-09-19 20:50 ` [RFC 09/20] x86/vdso/timens: Add offsets page in vvar Dmitry Safonov
2018-09-19 20:50 ` [RFC 10/20] x86/vdso: Use set_normalized_timespec() to avoid 32 bit overflow Dmitry Safonov
2018-09-19 20:50 ` [RFC 11/20] x86/vdso: Purge timens page on setns()/unshare()/clone() Dmitry Safonov
2018-09-19 20:50 ` [RFC 12/20] x86/vdso: Look for vvar vma to purge timens page Dmitry Safonov
2018-09-19 20:50 ` [RFC 13/20] posix-timers/timens: Take into account clock offsets Dmitry Safonov
2018-09-30 3:11 ` [LKP] [posix] 25217c6e39: BUG:KASAN:null-ptr-deref_in_c kernel test robot
2018-09-19 20:50 ` [RFC 14/20] timens: Add align for timens_offsets Dmitry Safonov
2018-09-19 20:50 ` [RFC 15/20] timens: Optimize zero-offsets Dmitry Safonov
2018-09-19 20:50 ` [RFC 16/20] selftest: Add Time Namespace test for supported clocks Dmitry Safonov
2018-09-24 21:36 ` Shuah Khan
2018-09-19 20:50 ` [RFC 17/20] selftest/timens: Add test for timerfd Dmitry Safonov
2018-09-19 20:50 ` [RFC 18/20] selftest/timens: Add test for clock_nanosleep Dmitry Safonov
2018-09-19 20:50 ` [RFC 19/20] timens/selftest: Add procfs selftest Dmitry Safonov
2018-09-19 20:50 ` [RFC 20/20] timens/selftest: Add timer offsets test Dmitry Safonov
2018-09-21 12:27 ` [RFC 00/20] ns: Introduce Time Namespace Eric W. Biederman
2018-09-24 20:51 ` Andrey Vagin
2018-09-24 22:02 ` Eric W. Biederman
2018-09-25 1:42 ` Andrey Vagin
2018-09-26 17:36 ` Eric W. Biederman
2018-09-26 17:59 ` Dmitry Safonov
2018-09-27 21:30 ` Thomas Gleixner
2018-09-27 21:41 ` Thomas Gleixner
2018-10-01 23:20 ` Andrey Vagin [this message]
2018-10-02 6:15 ` Thomas Gleixner
2018-10-02 21:05 ` Dmitry Safonov
2018-10-02 21:26 ` Thomas Gleixner
2018-09-28 17:03 ` Eric W. Biederman
2018-09-28 19:32 ` Thomas Gleixner
2018-10-01 9:05 ` Eric W. Biederman
2018-10-01 9:15 ` Setting monotonic time? Eric W. Biederman
2018-10-01 18:52 ` Thomas Gleixner
2018-10-02 20:00 ` Arnd Bergmann
2018-10-02 20:06 ` Thomas Gleixner
2018-10-03 4:50 ` Eric W. Biederman
2018-10-03 5:25 ` Thomas Gleixner
2018-10-03 6:14 ` Eric W. Biederman
2018-10-03 7:02 ` Arnd Bergmann
2018-10-03 6:14 ` Thomas Gleixner
2018-10-01 20:51 ` Andrey Vagin
2018-10-02 6:16 ` Thomas Gleixner
2018-10-21 1:41 ` [RFC 00/20] ns: Introduce Time Namespace Andrei Vagin
2018-10-21 3:54 ` Andrei Vagin
2018-10-29 20:33 ` Thomas Gleixner
2018-10-29 21:21 ` Eric W. Biederman
2018-10-29 21:36 ` Thomas Gleixner
2018-10-31 16:26 ` Andrei Vagin
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