linux-kernel - Re: asm-generic: Disallow no-op mb() for SMP systems

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Message-ID: <20180203114240.GU2269@hirez.programming.kicks-ass.net>
Date:   Sat, 3 Feb 2018 12:42:40 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alan Cox <gnomes@...rguk.ukuu.org.uk>
Cc:     kbuild test robot <lkp@...el.com>, kbuild-all@...org,
        Stafford Horne <shorne@...il.com>,
        Will Deacon <will.deacon@....com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        David Howells <dhowells@...hat.com>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: asm-generic: Disallow no-op mb() for SMP systems

On Fri, Feb 02, 2018 at 09:08:20PM +0000, Alan Cox wrote:
> On Fri, 2 Feb 2018 21:25:49 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Sat, Feb 03, 2018 at 04:00:35AM +0800, kbuild test robot wrote:
> > > Hi Peter,
> > > 
> > > I love your patch! Yet something to improve:  
> > 
> > Seriously? Bots have feelings?
> > 
> > > [auto build test ERROR on asm-generic/master]
> > > [also build test ERROR on v4.15 next-20180202]
> > > [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> > > 
> > > url:    https://github.com/0day-ci/linux/commits/Peter-Zijlstra/asm-generic-Disallow-no-op-mb-for-SMP-systems/20180203-000108
> > > base:   https://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic.git master
> > > config: m32r-usrv_defconfig (attached as .config)
> > > compiler: m32r-linux-gcc (GCC) 7.2.0  
> > 
> > Awesome, another broken architecture.. and this one is Orphaned :-(
> > No maintainer to bug..
> 
> Renesas claim to still support the processor family so perhaps they can
> provide a maintainer if you instead submit a patch to remove it from the
> tree ;-)

There's an idea :-)

> From the documentation however the processor only does explicit dual
> issue instructions, and the SMP is cache coherent so I'm not convinced
> there is a problem with it.

Thanks for looking at that, got a link handy to said documentation? Does
it really not have a store-buffer?

Getting such details sorted was exactly the purpose of the patch, so in
that regards its a success :-)