linux-kernel - Re: Memory barrier needed with wake_up

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Message-ID: <20160906111052.GZ10121@twins.programming.kicks-ass.net>
Date:   Tue, 6 Sep 2016 13:10:52 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Will Deacon <will.deacon@....com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...hat.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        USB list <linux-usb@...r.kernel.org>,
        Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: Memory barrier needed with wake_up_process()?

On Mon, Sep 05, 2016 at 10:43:11AM +0100, Will Deacon wrote:
> On Sat, Sep 03, 2016 at 12:16:29AM +0200, Peter Zijlstra wrote:

> > Forgot to Cc Will. Will, does ARM64 need to make smp_mb__before_spinlock
> > smp_mb() too?
> 
> Yes, probably. Just to confirm, the test is something like:
> 
> 
> CPU0
> ----
> 
> Wx=1
> smp_mb__before_spinlock()
> LOCK(y)
> Rz=0
> 
> CPU1
> ----
> 
> Wz=1
> smp_mb()
> Rx=0
> 
> 
> and that should be forbidden?

Indeed.