linux-kernel - Re: [RFC PATCH v2 1/2] membarrier: Provide register expedited private command

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Message-ID: <20170921121344.movkcoj6rm2s23ig@hirez.programming.kicks-ass.net>
Date:   Thu, 21 Sep 2017 14:13:44 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, Boqun Feng <boqun.feng@...il.com>,
        Andrew Hunter <ahh@...gle.com>,
        Maged Michael <maged.michael@...il.com>, gromer@...gle.com,
        Avi Kivity <avi@...lladb.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Dave Watson <davejwatson@...com>,
        Alan Stern <stern@...land.harvard.edu>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...nel.org>, linux-arch@...r.kernel.org
Subject: Re: [RFC PATCH v2 1/2] membarrier: Provide register expedited
 private command

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);