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SubjectRe: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering

* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:

> On Sun, Jan 15, 2017 at 10:40:58AM +0100, Ingo Molnar wrote:
> >
> > * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
> >
> > > > [sounds of rummaging around in the Git tree]
> > > >
> > > > I found this commit of yours from ancient history (more than a year ago!):
> > > >
> > > > commit 12d560f4ea87030667438a169912380be00cea4b
> > > > Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > > Date: Tue Jul 14 18:35:23 2015 -0700
> > > >
> > > > rcu,locking: Privatize smp_mb__after_unlock_lock()
> > > >
> > > > RCU is the only thing that uses smp_mb__after_unlock_lock(), and is
> > > > likely the only thing that ever will use it, so this commit makes this
> > > > macro private to RCU.
> > > >
> > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > > Cc: Will Deacon <will.deacon@arm.com>
> > > > Cc: Peter Zijlstra <peterz@infradead.org>
> > > > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > > > Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
> > > >
> > > > So I concur and I'm fine with your patch - or with the status quo code as well.
> > >
> > > I already have the patch queued, so how about I keep it if I get an ack
> > > from the powerpc guys and drop it otherwise?
> >
> > Yeah, sounds good! Your patch made me look up 'RelAcq' so it has documentation
> > value as well ;-)
>
> ;-) ;-) ;-)
>
> Looking forward, my guess would be that if some other code needs
> smp_mb__after_unlock_lock() or if some other architecture needs
> non-smb_mb() special handling, I should consider making it work the
> same as smp_mb__after_atomic() and friends. Does that seem like a
> reasonable thought?

Yeah, absolutely - it's just that the pattern triggered the 'this looks a bit too
specialized' response in me, but after seeing the details (again ...) I agree that
this time is different!

Thanks,

Ingo

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