x86, asm: Clean up and simplify <asm/cmpxchg.h>
Remove the __xg() hack to create a memory barrier near xchg and
cmpxchg; it has been there since 1.3.11 but should not be necessary
with "asm volatile" and a "memory" clobber, neither of which were
there in the original implementation.
However, we *should* make this a volatile reference.
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
LKML-Reference: <AANLkTikAmaDPji-TVDarmG1yD=fwbffcsmEU=YEuP+8r@mail.gmail.com>
diff --git a/arch/x86/include/asm/cmpxchg_64.h b/arch/x86/include/asm/cmpxchg_64.h
index 9596e7c..423ae58 100644
--- a/arch/x86/include/asm/cmpxchg_64.h
+++ b/arch/x86/include/asm/cmpxchg_64.h
@@ -3,8 +3,6 @@
#include <asm/alternative.h> /* Provides LOCK_PREFIX */
-#define __xg(x) ((volatile long *)(x))
-
static inline void set_64bit(volatile u64 *ptr, u64 val)
{
*ptr = val;
@@ -14,38 +12,51 @@
extern void __cmpxchg_wrong_size(void);
/*
- * Note: no "lock" prefix even on SMP: xchg always implies lock anyway
- * Note 2: xchg has side effect, so that attribute volatile is necessary,
- * but generally the primitive is invalid, *ptr is output argument. --ANK
+ * Note: no "lock" prefix even on SMP: xchg always implies lock anyway.
+ * Since this is generally used to protect other memory information, we
+ * use "asm volatile" and "memory" clobbers to prevent gcc from moving
+ * information around.
*/
#define __xchg(x, ptr, size) \
({ \
__typeof(*(ptr)) __x = (x); \
switch (size) { \
case 1: \
- asm volatile("xchgb %b0,%1" \
- : "=q" (__x), "+m" (*__xg(ptr)) \
+ { \
+ volatile u8 *__ptr = (volatile u8 *)(ptr); \
+ asm volatile("xchgb %0,%1" \
+ : "=q" (__x), "+m" (*__ptr) \
: "0" (__x) \
: "memory"); \
break; \
+ } \
case 2: \
- asm volatile("xchgw %w0,%1" \
- : "=r" (__x), "+m" (*__xg(ptr)) \
+ { \
+ volatile u16 *__ptr = (volatile u16 *)(ptr); \
+ asm volatile("xchgw %0,%1" \
+ : "=r" (__x), "+m" (*__ptr) \
: "0" (__x) \
: "memory"); \
break; \
+ } \
case 4: \
- asm volatile("xchgl %k0,%1" \
- : "=r" (__x), "+m" (*__xg(ptr)) \
+ { \
+ volatile u32 *__ptr = (volatile u32 *)(ptr); \
+ asm volatile("xchgl %0,%1" \
+ : "=r" (__x), "+m" (*__ptr) \
: "0" (__x) \
: "memory"); \
break; \
+ } \
case 8: \
+ { \
+ volatile u64 *__ptr = (volatile u64 *)(ptr); \
asm volatile("xchgq %0,%1" \
- : "=r" (__x), "+m" (*__xg(ptr)) \
+ : "=r" (__x), "+m" (*__ptr) \
: "0" (__x) \
: "memory"); \
break; \
+ } \
default: \
__xchg_wrong_size(); \
} \
@@ -69,29 +80,41 @@
__typeof__(*(ptr)) __new = (new); \
switch (size) { \
case 1: \
- asm volatile(lock "cmpxchgb %b2,%1" \
- : "=a" (__ret), "+m" (*__xg(ptr)) \
+ { \
+ volatile u8 *__ptr = (volatile u8 *)(ptr); \
+ asm volatile(lock "cmpxchgb %2,%1" \
+ : "=a" (__ret), "+m" (*__ptr) \
: "q" (__new), "0" (__old) \
: "memory"); \
break; \
+ } \
case 2: \
- asm volatile(lock "cmpxchgw %w2,%1" \
- : "=a" (__ret), "+m" (*__xg(ptr)) \
+ { \
+ volatile u16 *__ptr = (volatile u16 *)(ptr); \
+ asm volatile(lock "cmpxchgw %2,%1" \
+ : "=a" (__ret), "+m" (*__ptr) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
+ } \
case 4: \
- asm volatile(lock "cmpxchgl %k2,%1" \
- : "=a" (__ret), "+m" (*__xg(ptr)) \
+ { \
+ volatile u32 *__ptr = (volatile u32 *)(ptr); \
+ asm volatile(lock "cmpxchgl %2,%1" \
+ : "=a" (__ret), "+m" (*__ptr) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
+ } \
case 8: \
+ { \
+ volatile u64 *__ptr = (volatile u64 *)(ptr); \
asm volatile(lock "cmpxchgq %2,%1" \
- : "=a" (__ret), "+m" (*__xg(ptr)) \
+ : "=a" (__ret), "+m" (*__ptr) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
+ } \
default: \
__cmpxchg_wrong_size(); \
} \