Subject: Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory
 barrier (v5)
From: Peter Zijlstra <peterz@infradead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@elte.hu>,
       akpm@linux-foundation.org, josh@joshtriplett.org, tglx@linutronix.de,
       Valdis.Kletnieks@vt.edu, dhowells@redhat.com, laijs@cn.fujitsu.com,
       dipankar@in.ibm.com
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Date: Thu, 21 Jan 2010 12:26:52 +0100
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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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