On Mon, Jan 23, 2017 at 07:12:03PM +1100, Michael Ellerman wrote:
> "Paul E. McKenney" <paul...@linux.vnet.ibm.com> writes:
>
> > On Sat, Jan 14, 2017 at 11:54:17AM -0800, Paul E. McKenney wrote:
> >> On Sat, Jan 14, 2017 at 10:35:50AM +0100, Ingo Molnar wrote:
> >> > * Paul E. McKenney <paul...@linux.vnet.ibm.com> wrote:
> >
> > [ . . . ]
> >
> >> > > + */
> >> > > +#ifdef CONFIG_PPC
> >> > > +#define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for
> >> > > lock. */
> >> > > +#else /* #ifdef CONFIG_PPC */
> >> > > +#define smp_mb__after_unlock_lock() do { } while (0)
> >> > > +#endif /* #else #ifdef CONFIG_PPC */
> >> >
> >> > Yeah, so I realize that this was pre-existing code, but putting
> >> > CONFIG_$ARCH
> >> > #ifdefs into generic headers is generally frowned upon.
> >> >
> >> > The canonical approach would be either to define a helper Kconfig
> >> > variable that
> >> > can be set by PPC (but other architectures don't need to set it), or to
> >> > expose a
> >> > suitable macro (function) for architectures to define in their barrier.h
> >> > arch
> >> > header file.
> >>
> >> Very well, I will add a separate commit for this. 4.11 OK?
> >
> > Does the patch below seem reasonable?
> >
> > Thanx, Paul
> >
> > ------------------------------------------------------------------------
> >
> > commit 271c0601237c41a279f975563e13837bace0df03
> > Author: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> > Date: Sat Jan 14 13:32:50 2017 -0800
> >
> > rcu: Make arch select smp_mb__after_unlock_lock() strength
> >
> > The definition of smp_mb__after_unlock_lock() is currently smp_mb()
> > for CONFIG_PPC and a no-op otherwise. It would be better to instead
> > provide an architecture-selectable Kconfig option, and select the
> > strength of smp_mb__after_unlock_lock() based on that option. This
> > commit therefore creates CONFIG_ARCH_WEAK_RELACQ, has PPC select it,
> > and bases the definition of smp_mb__after_unlock_lock() on this new
> > CONFIG_ARCH_WEAK_RELACQ Kconfig option.
> >
> > Reported-by: Ingo Molnar <mi...@kernel.org>
> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> > Cc: Peter Zijlstra <pet...@infradead.org>
> > Cc: Will Deacon <will.dea...@arm.com>
> > Cc: Boqun Feng <boqun.f...@linux.vnet.ibm.com>
> > Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
> > Cc: Paul Mackerras <pau...@samba.org>
> > Cc: Michael Ellerman <m...@ellerman.id.au>
> > Cc: <linuxppc-...@lists.ozlabs.org>
>
> Personally I'd call it ARCH_WEAK_RELEASE_ACQUIRE, which is longer but
> clearer I think. But it's not a big deal, so which ever you prefer.
ARCH_WEAK_RELEASE_ACQUIRE it is!
> Acked-by: Michael Ellerman <m...@ellerman.id.au>
Applied, thank you!
Thanx, Paul
