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

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Message-Id: <20170921152728.GF3521@linux.vnet.ibm.com>
Date:   Thu, 21 Sep 2017 08:27:28 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Andrew Hunter <ahh@...gle.com>,
        maged michael <maged.michael@...il.com>,
        gromer <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 <linux-arch@...r.kernel.org>
Subject: Re: [RFC PATCH v2 1/2] membarrier: Provide register expedited
 private command

On Thu, Sep 21, 2017 at 03:11:43PM +0000, Mathieu Desnoyers wrote:
> ----- On Sep 21, 2017, at 8:13 AM, Peter Zijlstra peterz@...radead.org wrote:
> 
> > 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.
> 
> Yes, it did indeed explode spectacularly at boot in testing. RFC v3 fixes that.

Good to hear that there is a useful test.  ;-)

							Thanx, Paul

> Thanks,
> 
> Mathieu
> 
> 
> > 
> >>  	} else {
> >>  		rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);
> > >  		rq_unlock_irq(rq, &rf);
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
>