linux-kernel - Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier (v5)

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Date:	Thu, 21 Jan 2010 12:26:52 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org, josh@...htriplett.org,
	tglx@...utronix.de, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	laijs@...fujitsu.com, dipankar@...ibm.com
Subject: Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory
 barrier (v5)

On Tue, 2010-01-19 at 20:06 +0100, Peter Zijlstra wrote:
> 
> We could possibly look at placing that assignment in context_switch()
> between switch_mm() and switch_to(), which should provide a mb before
> and after I think, Ingo?

Right, just found out why we cannot do that, the first thing
context_switch() does is prepare_context_switch() which includes
prepare_lock_switch() which on __ARCH_WANT_UNLOCKED_CTXSW machines drops
the rq->lock, and we have to have rq->curr assigned by then.



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