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Date: Mon, 16 Mar 2015 18:13:34 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: linux-kernel@vger.kernel.org,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Steven Rostedt <rostedt@goodmis.org>,
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        Thomas Gleixner <tglx@linutronix.de>,
        David Howells <dhowells@redhat.com>, Nick Piggin <npiggin@kernel.dk>
Subject: Re: [RFC PATCH] sys_membarrier(): system/process-wide memory barrier
 (x86) (v12)
Message-ID: <20150316171334.GG21418@twins.programming.kicks-ass.net>
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On Mon, Mar 16, 2015 at 03:43:56PM +0000, Mathieu Desnoyers wrote:
> > > +++ b/arch/x86/include/asm/mmu_context.h

> > In both cases the cpumask_set_cpu() will also imply a MB.
> 
> I'm probably missing what exactly in cpumask_set_cpu()
> implies this guarantee. cpumask_set_cpu() uses set_bit().
> On x86, set_bit is indeed implemented with a lock-prefixed
> orb or bts. However, the comment above set_bit() states:

But its very much x86 specific code you're patching, so the LOCK prefix
is sufficient ;-)