[PATCH] x86/atomic: Add arch_atomic_not()

[Ziran Zhang <zhangcoder@yeah.net>]

The kernel already has non-atomic bitmap_complement(), but
no direct atomic implementation.

According to Intel and AMD manuals, the NOT instruction
supports a LOCK prefix.

Currently the only way to achieve this is arch_atomic_xor(-1, v),
which is non-obvious and hurts readability, so add arch_atomic_not()
to provide an explicit atomic complement operation.

Signed-off-by: Ziran Zhang <zhangcoder@yeah.net>
---
 arch/x86/include/asm/atomic.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/include/asm/atomic.h b/arch/x86/include/asm/atomic.h
index 75743f1df..d7e543194 100644
--- a/arch/x86/include/asm/atomic.h
+++ b/arch/x86/include/asm/atomic.h
@@ -168,6 +168,13 @@ static __always_inline int arch_atomic_fetch_xor(int i, atomic_t *v)
 }
 #define arch_atomic_fetch_xor arch_atomic_fetch_xor
 
+static __always_inline void arch_atomic_not(atomic_t *v)
+{
+	asm_inline volatile(LOCK_PREFIX "notl %0"
+			: "+m" (v->counter) :: "memory");
+}
+#define arch_atomic_not arch_atomic_not
+
 #ifdef CONFIG_X86_32
 # include <asm/atomic64_32.h>
 #else
-- 
2.51.0