linux-kernel - Re: [RFC][PATCH] mips: Fix arch_spin

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Date:	Tue, 2 Feb 2016 14:38:10 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Boqun Feng <boqun.feng@...il.com>,
	Will Deacon <will.deacon@....com>,
	"Maciej W. Rozycki" <macro@...tec.com>,
	David Daney <ddaney@...iumnetworks.com>,
	Måns Rullgård <mans@...sr.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org
Subject: Re: [RFC][PATCH] mips: Fix arch_spin_unlock()

On Tue, Feb 02, 2016 at 06:23:37PM +0100, Peter Zijlstra wrote:
> 
> 
> On 2 February 2016 07:44:33 CET, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> >
> >> If so, do we also need to take the following pairing into
> >consideration?
> >> 
> >> o	smp_store_release() -> READ_ONCE(); if ;smp_rmb(); <ACCESS_ONCE()>
> 
> 
> We rely on this with smp_cond_aquire() to extend the chain.

We do indeed!  And it is not possible to use smp_load_acquire() given
this API becauseof the "!".  Hmmm...

If this one turns out to be problematic, there are some ways of dealing
with it.  But thank you for reminding me of it.  I think, anyway.  ;-)

							Thanx, Paul