linux-kernel - Re: [RFC PATCH v3 1/2] membarrier: Provide register expedited private command

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Message-ID: <20170925122510.2uxm54thizcupgpk@hirez.programming.kicks-ass.net>
Date:   Mon, 25 Sep 2017 14:25:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        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 v3 1/2] membarrier: Provide register expedited
 private command

On Mon, Sep 25, 2017 at 08:10:54PM +0800, Boqun Feng wrote:
> > static void membarrier_register_private_expedited(void)
> > {
> >         struct task_struct *p = current;
> > 
> >         if (READ_ONCE(p->mm->membarrier_private_expedited))
> >                 return;
> >         membarrier_arch_register_private_expedited(p);

Should we not then also do:

	    barrier();

> >         WRITE_ONCE(p->mm->membarrier_private_expedited, 1);
> > }

to avoid the compiler lifting that store?