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Date: Tue, 2 Feb 2016 17:37:35 +0000
From: Will Deacon <will.deacon@arm.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Boqun Feng <boqun.feng@gmail.com>, Peter Zijlstra <peterz@infradead.org>,
        "Maciej W. Rozycki" <macro@imgtec.com>,
        David Daney <ddaney@caviumnetworks.com>,
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        Ralf Baechle <ralf@linux-mips.org>, linux-kernel@vger.kernel.org,
        torvalds@linux-foundation.org
Subject: Re: [RFC][PATCH] mips: Fix arch_spin_unlock()
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On Tue, Feb 02, 2016 at 09:12:37AM -0800, Paul E. McKenney wrote:
> On Tue, Feb 02, 2016 at 12:20:25PM +0000, Will Deacon wrote:
> > On Tue, Feb 02, 2016 at 08:12:30PM +0800, Boqun Feng wrote:
> > > On Tue, Feb 02, 2016 at 11:45:59AM +0000, Will Deacon wrote:
> > > > Well, the following ISA2 test is permitted on ARM:
> > > > 
> > > > 
> > > > P0:
> > > > Wx=1
> > > > WyRel=1	// rcu_assign_pointer
> > > > 
> > > > P1:
> > > > Ry=1	// rcu_dereference
> > > 
> > > What if a <addr> dependency is added here? Same result?
> > 
> > Right, that fixes it. So if we're only considering things like:
> > 
> >   rcu_dereference
> >   <addr>
> >   RELEASE
> > 
> > then local transitivity should be preserved.
> 
> Whew!!!  ;-)
> 
> > I think the same applies to <ctrl>, which seems to match your later
> > example.
> 
> Could you please check?

I should've been more concrete here: it does indeed apply if you replace
the <addr> with a <ctrl> in the snippet above, I just hadn't got Boqun's
example paged in and didn't want to commit on the examples being identical.

Will