[Xen-devel] [PATCH RFC] smp_store_mb should use smp_mb

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

On some architectures smp_store_mb() calls mb() which is stronger
than implied by both the name and the documentation.

smp_store_mb is only used by core kernel code at the moment, so
we know no one mis-uses it for an MMIO barrier.
Make it call smp_mb consistently before some arch-specific
code uses it as such by mistake.

Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>

---

Note: I'm guessing an ack from arch maintainers will be needed, but
I'm working on a bigger cleanup moving a bunch of duplicated code
into asm-generic/barrier.h which depends on this, so not Cc'ing
widely yet.

Please Ack if appropriate but do not merge yet.

diff --git a/arch/ia64/include/asm/barrier.h b/arch/ia64/include/asm/barrier.h
index df896a1..425552b 100644
--- a/arch/ia64/include/asm/barrier.h
+++ b/arch/ia64/include/asm/barrier.h
@@ -77,7 +77,7 @@ do {                                                          
        \
        ___p1;                                                          \
 })
 
-#define smp_store_mb(var, value)       do { WRITE_ONCE(var, value); mb(); } 
while (0)
+#define smp_store_mb(var, value)       do { WRITE_ONCE(var, value); smp_mb(); 
} while (0)
 
 /*
  * The group barrier in front of the rsm & ssm are necessary to ensure
diff --git a/arch/powerpc/include/asm/barrier.h 
b/arch/powerpc/include/asm/barrier.h
index 0eca6ef..4f0169e 100644
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -34,7 +34,7 @@
 #define rmb()  __asm__ __volatile__ ("sync" : : : "memory")
 #define wmb()  __asm__ __volatile__ ("sync" : : : "memory")
 
-#define smp_store_mb(var, value)       do { WRITE_ONCE(var, value); mb(); } 
while (0)
+#define smp_store_mb(var, value)       do { WRITE_ONCE(var, value); smp_mb(); 
} while (0)
 
 #ifdef __SUBARCH_HAS_LWSYNC
 #    define SMPWMB      LWSYNC
diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h
index d68e11e..6c1d8b5 100644
--- a/arch/s390/include/asm/barrier.h
+++ b/arch/s390/include/asm/barrier.h
@@ -36,7 +36,7 @@
 #define smp_mb__before_atomic()                smp_mb()
 #define smp_mb__after_atomic()         smp_mb()
 
-#define smp_store_mb(var, value)               do { WRITE_ONCE(var, value); 
mb(); } while (0)
+#define smp_store_mb(var, value)               do { WRITE_ONCE(var, value); 
smp_mb(); } while (0)
 
 #define smp_store_release(p, v)                                                
\
 do {                                                                   \
diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index b42afad..0f45f93 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -93,7 +93,7 @@
 #endif /* CONFIG_SMP */
 
 #ifndef smp_store_mb
-#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); mb(); } while 
(0)
+#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); smp_mb(); } 
while (0)
 #endif
 
 #ifndef smp_mb__before_atomic

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