"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-dev@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.
Acked-by: Michael Ellerman <m...@ellerman.id.au>
cheers
