linux-kernel - Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option

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Date:   Tue, 25 Jul 2017 22:39:53 +0000 (UTC)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        dipankar <dipankar@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Triplett <josh@...htriplett.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        rostedt <rostedt@...dmis.org>,
        David Howells <dhowells@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        fweisbec <fweisbec@...il.com>, Oleg Nesterov <oleg@...hat.com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option

----- On Jul 25, 2017, at 5:55 PM, Peter Zijlstra peterz@...radead.org wrote:

> On Tue, Jul 25, 2017 at 02:19:26PM -0700, Paul E. McKenney wrote:
>> On Tue, Jul 25, 2017 at 10:24:51PM +0200, Peter Zijlstra wrote:
>> > On Tue, Jul 25, 2017 at 12:36:12PM -0700, Paul E. McKenney wrote:
>> > 
>> > > There are a lot of variations, to be sure.  For whatever it is worth,
>> > > the original patch that started this uses mprotect():
>> > > 
>> > > https://github.com/msullivan/userspace-rcu/commit/04656b468d418efbc5d934ab07954eb8395a7ab0
>> > 
>> > FWIW that will not work on s390 (and maybe others), they don't in fact
>> > require IPIs for remote TLB invalidation.
>> 
>> Nor will it for ARM.  Nor (I think) for PowerPC.  But that is in fact
>> what people are doing right now in real life.  Hence my renewed interest
>> in sys_membarrier().
> 
> People always do crazy stuff, but what surprised me is that such s patch
> got merged in urcu even though its known broken for a number of
> architectures.

As maintainer of liburcu, I can certainly say that this patch never made it into
liburcu master branch (official repo at git://git.liburcu.org/userspace-rcu.git).
Paul is referring to a liburcu fork by a github user "msullivan", not the official
tree.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com