locking/arch: Add WRITE_ONCE() to set_mb()

Since we assume set_mb() to result in a single store followed by a
full memory barrier, employ WRITE_ONCE().

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/arm/include/asm/barrier.h b/arch/arm/include/asm/barrier.h
index d2f81e6..993150a 100644 (file)
--- a/arch/arm/include/asm/barrier.h
+++ b/arch/arm/include/asm/barrier.h
@@ -81,7 +81,7 @@ do {                                                                  \
 #define read_barrier_depends()         do { } while(0)
 #define smp_read_barrier_depends()     do { } while(0)
 
-#define set_mb(var, value)     do { var = value; smp_mb(); } while (0)
+#define set_mb(var, value)     do { WRITE_ONCE(var, value); smp_mb(); } while (0)
 
 #define smp_mb__before_atomic()        smp_mb()
 #define smp_mb__after_atomic() smp_mb()

diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
index 71f19c4..ff7de78 100644 (file)
--- a/arch/arm64/include/asm/barrier.h
+++ b/arch/arm64/include/asm/barrier.h
@@ -114,7 +114,7 @@ do {                                                                        \
 #define read_barrier_depends()         do { } while(0)
 #define smp_read_barrier_depends()     do { } while(0)
 
-#define set_mb(var, value)     do { var = value; smp_mb(); } while (0)
+#define set_mb(var, value)     do { WRITE_ONCE(var, value); smp_mb(); } while (0)
 #define nop()          asm volatile("nop");
 
 #define smp_mb__before_atomic()        smp_mb()

diff --git a/arch/ia64/include/asm/barrier.h b/arch/ia64/include/asm/barrier.h
index f6769eb..03117e7 100644 (file)
--- a/arch/ia64/include/asm/barrier.h
+++ b/arch/ia64/include/asm/barrier.h
@@ -82,7 +82,7 @@ do {                                                                  \
  * acquire vs release semantics but we can't discuss this stuff with
  * Linus just yet.  Grrr...
  */
-#define set_mb(var, value)     do { (var) = (value); mb(); } while (0)
+#define set_mb(var, value)     do { WRITE_ONCE(var, value); mb(); } while (0)
 
 /*
  * The group barrier in front of the rsm & ssm are necessary to ensure

diff --git a/arch/metag/include/asm/barrier.h b/arch/metag/include/asm/barrier.h
index d703d8e..97eb018 100644 (file)
--- a/arch/metag/include/asm/barrier.h
+++ b/arch/metag/include/asm/barrier.h
@@ -84,7 +84,7 @@ static inline void fence(void)
 #define read_barrier_depends()         do { } while (0)
 #define smp_read_barrier_depends()     do { } while (0)
 
-#define set_mb(var, value) do { var = value; smp_mb(); } while (0)
+#define set_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0)
 
 #define smp_store_release(p, v)                                                \
 do {                                                                   \

diff --git a/arch/mips/include/asm/barrier.h b/arch/mips/include/asm/barrier.h
index 2b8bbbc..cff1bbd 100644 (file)
--- a/arch/mips/include/asm/barrier.h
+++ b/arch/mips/include/asm/barrier.h
@@ -113,7 +113,7 @@
 #endif
 
 #define set_mb(var, value) \
-       do { var = value; smp_mb(); } while (0)
+       do { WRITE_ONCE(var, value); smp_mb(); } while (0)
 
 #define smp_llsc_mb()  __asm__ __volatile__(__WEAK_LLSC_MB : : :"memory")
 

diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
index a3bf5be..2a072e4 100644 (file)
--- 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 set_mb(var, value)     do { var = value; mb(); } while (0)
+#define set_mb(var, value)     do { WRITE_ONCE(var, value); 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 8d72471..b66cd53 100644 (file)
--- 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 set_mb(var, value)             do { var = value; mb(); } while (0)
+#define set_mb(var, value)             do { WRITE_ONCE(var, value); mb(); } while (0)
 
 #define smp_store_release(p, v)                                                \
 do {                                                                   \

diff --git a/arch/sparc/include/asm/barrier_64.h b/arch/sparc/include/asm/barrier_64.h
index 7664894..125fec7 100644 (file)
--- a/arch/sparc/include/asm/barrier_64.h
+++ b/arch/sparc/include/asm/barrier_64.h
@@ -41,7 +41,7 @@ do {  __asm__ __volatile__("ba,pt     %%xcc, 1f\n\t" \
 #define dma_wmb()      wmb()
 
 #define set_mb(__var, __value) \
-       do { __var = __value; membar_safe("#StoreLoad"); } while(0)
+       do { WRITE_ONCE(__var, __value); membar_safe("#StoreLoad"); } while(0)
 
 #ifdef CONFIG_SMP
 #define smp_mb()       mb()

diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h
index 959e45b..9de5cde 100644 (file)
--- a/arch/x86/include/asm/barrier.h
+++ b/arch/x86/include/asm/barrier.h
@@ -40,7 +40,7 @@
 #define smp_mb()       barrier()
 #define smp_rmb()      barrier()
 #define smp_wmb()      barrier()
-#define set_mb(var, value) do { var = value; barrier(); } while (0)
+#define set_mb(var, value) do { WRITE_ONCE(var, value); barrier(); } while (0)
 #endif /* SMP */
 
 #define read_barrier_depends()         do { } while (0)

diff --git a/arch/x86/um/asm/barrier.h b/arch/x86/um/asm/barrier.h
index 7e8a1a6..cc0cb01 100644 (file)
--- a/arch/x86/um/asm/barrier.h
+++ b/arch/x86/um/asm/barrier.h
@@ -39,7 +39,7 @@
 #define smp_mb()       barrier()
 #define smp_rmb()      barrier()
 #define smp_wmb()      barrier()
-#define set_mb(var, value) do { var = value; barrier(); } while (0)
+#define set_mb(var, value) do { WRITE_ONCE(var, value); barrier(); } while (0)
 
 #define read_barrier_depends()         do { } while (0)
 #define smp_read_barrier_depends()     do { } while (0)

diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index f5c40b0..3938716 100644 (file)
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -67,7 +67,7 @@
 #endif
 
 #ifndef set_mb
-#define set_mb(var, value)  do { (var) = (value); mb(); } while (0)
+#define set_mb(var, value)  do { WRITE_ONCE(var, value); mb(); } while (0)
 #endif
 
 #ifndef smp_mb__before_atomic

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index a7c0941..03e227b 100644 (file)
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -250,7 +250,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
        ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
 
 #define WRITE_ONCE(x, val) \
-       ({ typeof(x) __val = (val); __write_once_size(&(x), &__val, sizeof(__val)); __val; })
+       ({ union { typeof(x) __val; char __c[1]; } __u = { .__val = (val) }; __write_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
 
 #endif /* __KERNEL__ */