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>
diff --git a/arch/Kconfig b/arch/Kconfig
index 99839c23d453..94dd90d33f95 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -316,6 +316,9 @@ config HAVE_CMPXCHG_LOCAL
config HAVE_CMPXCHG_DOUBLE
bool
+config ARCH_WEAK_RELACQ
+ bool
+
config ARCH_WANT_IPC_PARSE_VERSION
bool
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index a8ee573fe610..e7083d27271e 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -165,6 +165,7 @@ config PPC
select HAVE_ARCH_HARDENED_USERCOPY
select HAVE_KERNEL_GZIP
select HAVE_CC_STACKPROTECTOR
+ select ARCH_WEAK_RELACQ
config GENERIC_CSUM
def_bool CPU_LITTLE_ENDIAN
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 357b32aaea48..5fdfe874229e 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -1175,11 +1175,11 @@ do { \
* if the UNLOCK and LOCK are executed by the same CPU or if the
* UNLOCK and LOCK operate on the same lock variable.
*/
-#ifdef CONFIG_PPC
+#ifdef CONFIG_ARCH_WEAK_RELACQ
#define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */
-#else /* #ifdef CONFIG_PPC */
+#else /* #ifdef CONFIG_ARCH_WEAK_RELACQ */
#define smp_mb__after_unlock_lock() do { } while (0)
-#endif /* #else #ifdef CONFIG_PPC */
+#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELACQ */
#endif /* __LINUX_RCUPDATE_H */
