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

[Paul E. McKenney]

On Sun, Jan 15, 2017 at 10:40:58AM +0100, Ingo Molnar wrote:
> 
> * Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
> > >   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@xxxxxxxxxxxxxxxxxx>
> > >     Cc: Will Deacon <will.deacon@xxxxxxx>
> > >     Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > >     Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> > >     Cc: "linux-arch@xxxxxxxxxxxxxxx" <linux-arch@xxxxxxxxxxxxxxx>
> > > 
> > > 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?

							Thanx, Paul