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

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Message-ID: <196603634.15769.1506006703406.JavaMail.zimbra@efficios.com>
Date:   Thu, 21 Sep 2017 15:11:43 +0000 (UTC)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        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 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.

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