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From: Andrei Vagin <avagin@gmail.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Dmitry Safonov <dima@arista.com>,
	linux-kernel@vger.kernel.org,
	Dmitry Safonov <0x7f454c46@gmail.com>,
	Andrei Vagin <avagin@openvz.org>, Adrian Reber <adrian@lisas.de>,
	Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Cyrill Gorcunov <gorcunov@openvz.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	Jann Horn <jannh@google.com>, Jeff Dike <jdike@addtoit.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Pavel Emelyanov <xemul@virtuozzo.com>,
	Shuah Khan <shuah@kernel.org>,
	containers@lists.linux-foundation.org, criu@openvz.org,
	linux-api@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCHv7 01/33] ns: Introduce Time Namespace
Date: Wed, 16 Oct 2019 16:33:42 -0700	[thread overview]
Message-ID: <20191016233342.GA3075@gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1910161230070.2046@nanos.tec.linutronix.de>

On Wed, Oct 16, 2019 at 12:39:11PM +0200, Thomas Gleixner wrote:
> On Wed, 16 Oct 2019, Vincenzo Frascino wrote:
> 
> < Trim 250+ lines ( 3+ pages) of pointlessly wasted electrons >
> 
> > > --- a/init/Kconfig
> > > +++ b/init/Kconfig
> > > @@ -1096,6 +1096,13 @@ config UTS_NS
> > >  	  In this namespace tasks see different info provided with the
> > >  	  uname() system call
> > >  
> > > +config TIME_NS
> > > +	bool "TIME namespace"
> > > +	default y
> > 
> > Having CONFIG_TIME_NS "default y" makes so that the option is selected even on
> > the architectures that have no support for time namespaces.
> > The direct consequence is that the fallbacks defined in this patch are never
> > selected and this ends up in kernel compilation errors due to missing symbols.
> > 
> > The error below shows what happens on arm64 (similar behavior on other
> > architectures):
> > 
> > aarch64-linux-gnu-ld: kernel/time/namespace.o: in function `timens_on_fork':
> > kernel/time/namespace.c:321: undefined reference to `vdso_join_timens'
> > 
> > My proposal is to keep TIME_NS "default n" (just remove "default y"), let the
> > architectures that enable time namespaces select it and make CONFIG_TIME_NS
> > select GENERIC_VDSO_TIME_NS if arch has HAVE_GENERIC_VDSO.
> 
> Nah.
> 
> config TIME_NS
> 	bool "TIME namespace"
> 	depends on GENERIC_VDSO_TIME_NS

I was thinking to fix this by the same way with a small difference.

If GENERIC_GETTIMEOFDAY isn't set, it should be safe to allow enabling
TIME_NS. In this case, clock_gettime works via system call and we don't
have arch-specific code in this case. Does this sound reasonable?

        depends on (!GENERIC_GETTIMEOFDAY || GENERIC_VDSO_TIME_NS)

Thanks,
Andrei

  parent reply	other threads:[~2019-10-16 23:33 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-11  1:23 [PATCHv7 00/33] kernel: Introduce Time Namespace Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 01/33] ns: " Dmitry Safonov
2019-10-16 10:27   ` Vincenzo Frascino
2019-10-16 10:39     ` Thomas Gleixner
2019-10-16 10:44       ` Vincenzo Frascino
2019-10-16 13:57         ` Dmitry Safonov
2019-10-16 23:33       ` Andrei Vagin [this message]
2019-10-17  9:20         ` Thomas Gleixner
2019-10-17  9:47           ` Vincenzo Frascino
2019-10-17  9:23         ` Vincenzo Frascino
2019-10-11  1:23 ` [PATCHv7 02/33] time: Add timens_offsets to be used for tasks in timens Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 03/33] posix-clocks: Rename the clock_get() callback to clock_get_timespec() Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 04/33] posix-clocks: Rename .clock_get_timespec() callbacks accordingly Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 05/33] alarmtimer: Rename gettime() callback to get_ktime() Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 06/33] alarmtimer: Provide get_timespec() callback Dmitry Safonov
2019-10-14  0:36   ` kbuild test robot
2019-10-11  1:23 ` [PATCHv7 07/33] posix-clocks: Introduce clock_get_ktime() callback Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 08/33] posix-timers: Use clock_get_ktime() in common_timer_get() Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 09/33] posix-clocks: Wire up clock_gettime() with timens offsets Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 10/33] kernel: Add do_timens_ktime_to_host() helper Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 11/33] timerfd: Make timerfd_settime() time namespace aware Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 12/33] posix-timers: Make timer_settime() " Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 13/33] alarmtimer: Make nanosleep " Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 14/33] hrtimers: Prepare hrtimer_nanosleep() for time namespaces Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 15/33] posix-timers: Make clock_nanosleep() time namespace aware Dmitry Safonov
2019-10-14  0:50   ` kbuild test robot
2019-10-14  4:10   ` kbuild test robot
2019-10-14 19:58     ` Andrey Vagin
2019-10-11  1:23 ` [PATCHv7 16/33] fs/proc: Respect boottime inside time namespace for /proc/uptime Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 17/33] x86/vdso: Restrict splitting VVAR VMA Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 18/33] lib/vdso: Add unlikely() hint into vdso_read_begin() Dmitry Safonov
2019-10-16 11:24   ` Vincenzo Frascino
2019-10-24  6:13     ` Andrei Vagin
2019-10-24  9:30       ` Vincenzo Frascino
2019-10-24 13:14         ` Vincenzo Frascino
2019-10-11  1:23 ` [PATCHv7 19/33] lib/vdso: Prepare for time namespace support Dmitry Safonov
2019-10-16 14:37   ` Vincenzo Frascino
2019-10-16 15:07     ` Thomas Gleixner
2019-10-16 16:36       ` Vincenzo Frascino
2019-10-11  1:23 ` [PATCHv7 20/33] x86/vdso: Provide vdso_data offset on vvar_page Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 21/33] x86/vdso: Add timens page Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 22/33] time: Allocate per-timens vvar page Dmitry Safonov
2019-10-14  2:22   ` kbuild test robot
2019-10-14  2:34   ` kbuild test robot
2019-10-11  1:23 ` [PATCHv7 23/33] x86/vdso: Handle faults on timens page Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 24/33] x86/vdso: On timens page fault prefault also VVAR page Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 25/33] x86/vdso: Zap vvar pages on switch a time namspace Dmitry Safonov
2019-10-14  2:47   ` kbuild test robot
2019-10-14  3:11   ` kbuild test robot
2019-10-11  1:23 ` [PATCHv7 26/33] fs/proc: Introduce /proc/pid/timens_offsets Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 27/33] selftests/timens: Add Time Namespace test for supported clocks Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 28/33] selftests/timens: Add a test for timerfd Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 29/33] selftests/timens: Add a test for clock_nanosleep() Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 30/33] selftests/timens: Add procfs selftest Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 31/33] selftests/timens: Add timer offsets test Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 32/33] selftests/timens: Add a simple perf test for clock_gettime() Dmitry Safonov
2019-10-11  1:23 ` [PATCHv7 33/33] selftests/timens: Check for right timens offsets after fork and exec Dmitry Safonov
2019-10-17  9:24 ` [PATCHv7 00/33] kernel: Introduce Time Namespace Thomas Gleixner
2019-10-17 23:47   ` Andrei Vagin
2019-10-22  8:45     ` Andrei Vagin

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