Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 16 Oct 2019 16:33:42 -0700
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
Message-ID: <20191016233342.GA3075@gmail.com>
References: <20191011012341.846266-1-dima@arista.com>
 <20191011012341.846266-2-dima@arista.com>
 <80af93da-d497-81de-2a2a-179bb3bc852d@arm.com>
 <alpine.DEB.2.21.1910161230070.2046@nanos.tec.linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=koi8-r
Content-Disposition: inline
In-Reply-To: <alpine.DEB.2.21.1910161230070.2046@nanos.tec.linutronix.de>
User-Agent: Mutt/1.12.1 (2019-06-15)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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