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Subject[PATCH] x86: fix and improve cmpxchg_double{,_local}()
Just like the per-CPU ones they had several problems/shortcomings:

Only the first memory operand was mentioned in the asm() operands, and
the 2x64-bit version didn't have a memory clobber while the 2x32-bit
one did. The former allowed the compiler to not recognize the need to
re-load the data in case it had it cached in some register, while the
latter was overly destructive.

The types of the local copies of the old and new values were incorrect
(the types of the pointed-to variables should be used here, to make
sure the respective old/new variable types are compatible).

The __dummy/__junk variables were pointless, given that local copies
of the inputs already existed (and can hence be used for discarded
outputs).

The 32-bit variant of cmpxchg_double_local() referenced
cmpxchg16b_local().

At once also
- change the return value type to what it really is: 'bool'
- unify 32- and 64-bit variants
- abstract out the common part of the 'normal' and 'local' variants

Signed-off-by: Jan Beulich <jbeulich@suse.com>

---
arch/x86/include/asm/cmpxchg.h | 23 +++++++++++++++++++
arch/x86/include/asm/cmpxchg_32.h | 46 --------------------------------------
arch/x86/include/asm/cmpxchg_64.h | 43 -----------------------------------
mm/slub.c | 4 +--
4 files changed, 25 insertions(+), 91 deletions(-)
--- 3.2-rc7/arch/x86/include/asm/cmpxchg.h
+++ 3.2-rc7-x86-cmpxchg-double/arch/x86/include/asm/cmpxchg.h
@@ -207,4 +207,27 @@ extern void __xadd_wrong_size(void)
#define xadd_sync(ptr, inc) __xadd((ptr), (inc), "lock; ")
#define xadd_local(ptr, inc) __xadd((ptr), (inc), "")

+#define __cmpxchg_double(pfx, p1, p2, o1, o2, n1, n2) \
+({ \
+ bool __ret; \
+ __typeof__(*(p1)) __old1 = (o1), __new1 = (n1); \
+ __typeof__(*(p2)) __old2 = (o2), __new2 = (n2); \
+ BUILD_BUG_ON(sizeof(*(p1)) != sizeof(long)); \
+ BUILD_BUG_ON(sizeof(*(p2)) != sizeof(long)); \
+ VM_BUG_ON((unsigned long)(p1) % (2 * sizeof(long))); \
+ VM_BUG_ON((unsigned long)((p1) + 1) != (unsigned long)(p2)); \
+ asm volatile(pfx "cmpxchg%c4b %2; sete %0" \
+ : "=a" (__ret), "+d" (__old2), \
+ "+m" (*(p1)), "+m" (*(p2)) \
+ : "i" (2 * sizeof(long)), "a" (__old1), \
+ "b" (__new1), "c" (__new2)); \
+ __ret; \
+})
+
+#define cmpxchg_double(p1, p2, o1, o2, n1, n2) \
+ __cmpxchg_double(LOCK_PREFIX, p1, p2, o1, o2, n1, n2)
+
+#define cmpxchg_double_local(p1, p2, o1, o2, n1, n2) \
+ __cmpxchg_double(, p1, p2, o1, o2, n1, n2)
+
#endif /* ASM_X86_CMPXCHG_H */
--- 3.2-rc7/arch/x86/include/asm/cmpxchg_32.h
+++ 3.2-rc7-x86-cmpxchg-double/arch/x86/include/asm/cmpxchg_32.h
@@ -166,52 +166,6 @@ static inline unsigned long cmpxchg_386(

#endif

-#define cmpxchg8b(ptr, o1, o2, n1, n2) \
-({ \
- char __ret; \
- __typeof__(o2) __dummy; \
- __typeof__(*(ptr)) __old1 = (o1); \
- __typeof__(o2) __old2 = (o2); \
- __typeof__(*(ptr)) __new1 = (n1); \
- __typeof__(o2) __new2 = (n2); \
- asm volatile(LOCK_PREFIX "cmpxchg8b %2; setz %1" \
- : "=d"(__dummy), "=a" (__ret), "+m" (*ptr)\
- : "a" (__old1), "d"(__old2), \
- "b" (__new1), "c" (__new2) \
- : "memory"); \
- __ret; })
-
-
-#define cmpxchg8b_local(ptr, o1, o2, n1, n2) \
-({ \
- char __ret; \
- __typeof__(o2) __dummy; \
- __typeof__(*(ptr)) __old1 = (o1); \
- __typeof__(o2) __old2 = (o2); \
- __typeof__(*(ptr)) __new1 = (n1); \
- __typeof__(o2) __new2 = (n2); \
- asm volatile("cmpxchg8b %2; setz %1" \
- : "=d"(__dummy), "=a"(__ret), "+m" (*ptr)\
- : "a" (__old), "d"(__old2), \
- "b" (__new1), "c" (__new2), \
- : "memory"); \
- __ret; })
-
-
-#define cmpxchg_double(ptr, o1, o2, n1, n2) \
-({ \
- BUILD_BUG_ON(sizeof(*(ptr)) != 4); \
- VM_BUG_ON((unsigned long)(ptr) % 8); \
- cmpxchg8b((ptr), (o1), (o2), (n1), (n2)); \
-})
-
-#define cmpxchg_double_local(ptr, o1, o2, n1, n2) \
-({ \
- BUILD_BUG_ON(sizeof(*(ptr)) != 4); \
- VM_BUG_ON((unsigned long)(ptr) % 8); \
- cmpxchg16b_local((ptr), (o1), (o2), (n1), (n2)); \
-})
-
#define system_has_cmpxchg_double() cpu_has_cx8

#endif /* _ASM_X86_CMPXCHG_32_H */
--- 3.2-rc7/arch/x86/include/asm/cmpxchg_64.h
+++ 3.2-rc7-x86-cmpxchg-double/arch/x86/include/asm/cmpxchg_64.h
@@ -20,49 +20,6 @@ static inline void set_64bit(volatile u6
cmpxchg_local((ptr), (o), (n)); \
})

-#define cmpxchg16b(ptr, o1, o2, n1, n2) \
-({ \
- char __ret; \
- __typeof__(o2) __junk; \
- __typeof__(*(ptr)) __old1 = (o1); \
- __typeof__(o2) __old2 = (o2); \
- __typeof__(*(ptr)) __new1 = (n1); \
- __typeof__(o2) __new2 = (n2); \
- asm volatile(LOCK_PREFIX "cmpxchg16b %2;setz %1" \
- : "=d"(__junk), "=a"(__ret), "+m" (*ptr) \
- : "b"(__new1), "c"(__new2), \
- "a"(__old1), "d"(__old2)); \
- __ret; })
-
-
-#define cmpxchg16b_local(ptr, o1, o2, n1, n2) \
-({ \
- char __ret; \
- __typeof__(o2) __junk; \
- __typeof__(*(ptr)) __old1 = (o1); \
- __typeof__(o2) __old2 = (o2); \
- __typeof__(*(ptr)) __new1 = (n1); \
- __typeof__(o2) __new2 = (n2); \
- asm volatile("cmpxchg16b %2;setz %1" \
- : "=d"(__junk), "=a"(__ret), "+m" (*ptr) \
- : "b"(__new1), "c"(__new2), \
- "a"(__old1), "d"(__old2)); \
- __ret; })
-
-#define cmpxchg_double(ptr, o1, o2, n1, n2) \
-({ \
- BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
- VM_BUG_ON((unsigned long)(ptr) % 16); \
- cmpxchg16b((ptr), (o1), (o2), (n1), (n2)); \
-})
-
-#define cmpxchg_double_local(ptr, o1, o2, n1, n2) \
-({ \
- BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
- VM_BUG_ON((unsigned long)(ptr) % 16); \
- cmpxchg16b_local((ptr), (o1), (o2), (n1), (n2)); \
-})
-
#define system_has_cmpxchg_double() cpu_has_cx16

#endif /* _ASM_X86_CMPXCHG_64_H */
--- 3.2-rc7/mm/slub.c
+++ 3.2-rc7-x86-cmpxchg-double/mm/slub.c
@@ -368,7 +368,7 @@ static inline bool __cmpxchg_double_slab
VM_BUG_ON(!irqs_disabled());
#ifdef CONFIG_CMPXCHG_DOUBLE
if (s->flags & __CMPXCHG_DOUBLE) {
- if (cmpxchg_double(&page->freelist,
+ if (cmpxchg_double(&page->freelist, &page->counters,
freelist_old, counters_old,
freelist_new, counters_new))
return 1;
@@ -402,7 +402,7 @@ static inline bool cmpxchg_double_slab(s
{
#ifdef CONFIG_CMPXCHG_DOUBLE
if (s->flags & __CMPXCHG_DOUBLE) {
- if (cmpxchg_double(&page->freelist,
+ if (cmpxchg_double(&page->freelist, &page->counters,
freelist_old, counters_old,
freelist_new, counters_new))
return 1;



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