Re: [PATCH] x86: Get rid of __HAVE_ARCH_CMPXCHG

[Borislav Petkov]

On Fri, Jul 11, 2014 at 12:35:43PM +0200, Geert Uytterhoeven wrote:
> In that case you also want to add a (new) "#define __HAVE_ARCH_CMPXCHG
> 1" to one of the shared x86 header files, right?

Yeah, I can't remove it after all. :-)

Diffstat is arch/x86/-only now, as it was supposed to be.

--
From: Borislav Petkov <bp@xxxxxxx>
Subject: [PATCH] x86: Simplify __HAVE_ARCH_CMPXCHG tests

Both the 32-bit and 64-bit cmpxchg.h header define __HAVE_ARCH_CMPXCHG
and there's ifdeffery which checks it. But since both bitness define it,
we can just as well move it up to the main cmpxchg header and simpify a
bit of code in doing that.

Signed-off-by: Borislav Petkov <bp@xxxxxxx>
---
 arch/x86/include/asm/cmpxchg.h     |  4 ++--
 arch/x86/include/asm/cmpxchg_32.h  |  2 --
 arch/x86/include/asm/cmpxchg_64.h  |  2 --
 arch/x86/include/asm/mc146818rtc.h |  2 +-
 arch/x86/include/asm/mutex_32.h    | 16 ++--------------
 arch/x86/kernel/acpi/boot.c        |  4 ----
 6 files changed, 5 insertions(+), 25 deletions(-)

diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h
index d47786acb016..99c105d78b7e 100644
--- a/arch/x86/include/asm/cmpxchg.h
+++ b/arch/x86/include/asm/cmpxchg.h
@@ -4,6 +4,8 @@
 #include <linux/compiler.h>
 #include <asm/alternative.h> /* Provides LOCK_PREFIX */
 
+#define __HAVE_ARCH_CMPXCHG 1
+
 /*
  * Non-existant functions to indicate usage errors at link time
  * (or compile-time if the compiler implements __compiletime_error().
@@ -143,7 +145,6 @@ extern void __add_wrong_size(void)
 # include <asm/cmpxchg_64.h>
 #endif
 
-#ifdef __HAVE_ARCH_CMPXCHG
 #define cmpxchg(ptr, old, new)						\
 	__cmpxchg(ptr, old, new, sizeof(*(ptr)))
 
@@ -152,7 +153,6 @@ extern void __add_wrong_size(void)
 
 #define cmpxchg_local(ptr, old, new)					\
 	__cmpxchg_local(ptr, old, new, sizeof(*(ptr)))
-#endif
 
 /*
  * xadd() adds "inc" to "*ptr" and atomically returns the previous
diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h
index f8bf2eecab86..f7e142926481 100644
--- a/arch/x86/include/asm/cmpxchg_32.h
+++ b/arch/x86/include/asm/cmpxchg_32.h
@@ -34,8 +34,6 @@ static inline void set_64bit(volatile u64 *ptr, u64 value)
 		     : "memory");
 }
 
-#define __HAVE_ARCH_CMPXCHG 1
-
 #ifdef CONFIG_X86_CMPXCHG64
 #define cmpxchg64(ptr, o, n)						\
 	((__typeof__(*(ptr)))__cmpxchg64((ptr), (unsigned long long)(o), \
diff --git a/arch/x86/include/asm/cmpxchg_64.h b/arch/x86/include/asm/cmpxchg_64.h
index 614be87f1a9b..1af94697aae5 100644
--- a/arch/x86/include/asm/cmpxchg_64.h
+++ b/arch/x86/include/asm/cmpxchg_64.h
@@ -6,8 +6,6 @@ static inline void set_64bit(volatile u64 *ptr, u64 val)
 	*ptr = val;
 }
 
-#define __HAVE_ARCH_CMPXCHG 1
-
 #define cmpxchg64(ptr, o, n)						\
 ({									\
 	BUILD_BUG_ON(sizeof(*(ptr)) != 8);				\
diff --git a/arch/x86/include/asm/mc146818rtc.h b/arch/x86/include/asm/mc146818rtc.h
index a55c7efcc4ed..0f555cc31984 100644
--- a/arch/x86/include/asm/mc146818rtc.h
+++ b/arch/x86/include/asm/mc146818rtc.h
@@ -13,7 +13,7 @@
 #define RTC_ALWAYS_BCD	1	/* RTC operates in binary mode */
 #endif
 
-#if defined(CONFIG_X86_32) && defined(__HAVE_ARCH_CMPXCHG)
+#if defined(CONFIG_X86_32)
 /*
  * This lock provides nmi access to the CMOS/RTC registers.  It has some
  * special properties.  It is owned by a CPU and stores the index register
diff --git a/arch/x86/include/asm/mutex_32.h b/arch/x86/include/asm/mutex_32.h
index 0208c3c2cbc6..85e6cda45a02 100644
--- a/arch/x86/include/asm/mutex_32.h
+++ b/arch/x86/include/asm/mutex_32.h
@@ -100,23 +100,11 @@ do {								\
 static inline int __mutex_fastpath_trylock(atomic_t *count,
 					   int (*fail_fn)(atomic_t *))
 {
-	/*
-	 * We have two variants here. The cmpxchg based one is the best one
-	 * because it never induce a false contention state.  It is included
-	 * here because architectures using the inc/dec algorithms over the
-	 * xchg ones are much more likely to support cmpxchg natively.
-	 *
-	 * If not we fall back to the spinlock based variant - that is
-	 * just as efficient (and simpler) as a 'destructive' probing of
-	 * the mutex state would be.
-	 */
-#ifdef __HAVE_ARCH_CMPXCHG
+	/* cmpxchg because it never induces a false contention state. */
 	if (likely(atomic_cmpxchg(count, 1, 0) == 1))
 		return 1;
+
 	return 0;
-#else
-	return fail_fn(count);
-#endif
 }
 
 #endif /* _ASM_X86_MUTEX_32_H */
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 86281ffb96d6..a531f6564ed0 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -74,10 +74,6 @@ int acpi_fix_pin2_polarity __initdata;
 static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;
 #endif
 
-#ifndef __HAVE_ARCH_CMPXCHG
-#warning ACPI uses CMPXCHG, i486 and later hardware
-#endif
-
 /* --------------------------------------------------------------------------
                               Boot-time Configuration
    -------------------------------------------------------------------------- */
-- 
2.0.0

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
--
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