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Date: Thu, 21 Sep 2017 14:13:44 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        linux-kernel@vger.kernel.org, Boqun Feng <boqun.feng@gmail.com>,
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        Avi Kivity <avi@scylladb.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Dave Watson <davejwatson@fb.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Will Deacon <will.deacon@arm.com>, Andy Lutomirski <luto@kernel.org>,
        linux-arch@vger.kernel.org
Subject: Re: [RFC PATCH v2 1/2] membarrier: Provide register expedited
 private command
Message-ID: <20170921121344.movkcoj6rm2s23ig@hirez.programming.kicks-ass.net>
References: <20170918223648.31505-1-mathieu.desnoyers@efficios.com>
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On Mon, Sep 18, 2017 at 06:36:47PM -0400, Mathieu Desnoyers wrote:
> @@ -3373,6 +3362,7 @@ static void __sched notrace __schedule(bool preempt)
>  
>  		/* Also unlocks the rq: */
>  		rq = context_switch(rq, prev, next, &rf);
> +		membarrier_arch_sched_in(prev, next);

That's wrong iirc; we just switched stacks, you cannot use @prev and
@next.

>  	} else {
>  		rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);
>  		rq_unlock_irq(rq, &rf);