On Mon, Jan 04, 2016 at 02:45:25PM +0100, Peter Zijlstra wrote:

On Thu, Dec 31, 2015 at 09:08:38PM +0200, Michael S. Tsirkin wrote:

quoted

This defines __smp_xxx barriers for s390,
for use by virtualization.

Some smp_xxx barriers are removed as they are
defined correctly by asm-generic/barriers.h

Note: smp_mb, smp_rmb and smp_wmb are defined as full barriers
unconditionally on this architecture.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/s390/include/asm/barrier.h | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h
index c358c31..fbd25b2 100644
--- a/arch/s390/include/asm/barrier.h
+++ b/arch/s390/include/asm/barrier.h

@@ -26,18 +26,21 @@
 #define wmb()				barrier()
 #define dma_rmb()			mb()
 #define dma_wmb()			mb()
-#define smp_mb()			mb()
-#define smp_rmb()			rmb()
-#define smp_wmb()			wmb()
-
-#define smp_store_release(p, v)						\
+#define __smp_mb()			mb()
+#define __smp_rmb()			rmb()
+#define __smp_wmb()			wmb()
+#define smp_mb()			__smp_mb()
+#define smp_rmb()			__smp_rmb()
+#define smp_wmb()			__smp_wmb()

Why define the smp_*mb() primitives here? Would not the inclusion of
asm-generic/barrier.h do this?

No because the generic one is a nop on !SMP, this one isn't.

Pls note this patch is just reordering code without making
functional changes.
And at the moment, on s390 smp_xxx barriers are always non empty.

Some of this could be sub-optimal, but
since on s390 Linux always runs on a hypervisor,
I am not sure it's safe to use the generic version -
in other words, it just might be that for s390 smp_ and virt_
barriers must be equivalent.

If in fact this turns out to be wrong, I can pick up
a patch to change this, but I'd rather make this
a patch on top so that my patches are testable
just by compiling and comparing the binary.

-- 
MST