locking/atomic: make ARCH_ATOMIC a Kconfig symbol

Subsequent patches will move architectures over to the ARCH_ATOMIC API,
after preparing the asm-generic atomic implementations to function with
or without ARCH_ATOMIC.

As some architectures use the asm-generic implementations exclusively
(and don't have a local atomic.h), and to avoid the risk that
ARCH_ATOMIC isn't defined in some cases we expect, let's make the
ARCH_ATOMIC macro a Kconfig symbol instead, so that we can guarantee it
is consistently available where needed.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210525140232.53872-2-mark.rutland@arm.com

arch/Kconfig

@@ -11,6 +11,9 @@ source "arch/$(SRCARCH)/Kconfig"
 
 menu "General architecture-dependent options"
 
+config ARCH_ATOMIC
+	bool
+
 config CRASH_CORE
 	bool
 

arch/arm64/Kconfig

@@ -9,6 +9,7 @@ config ARM64
 	select ACPI_MCFG if (ACPI && PCI)
 	select ACPI_SPCR_TABLE if ACPI
 	select ACPI_PPTT if ACPI
+	select ARCH_ATOMIC
 	select ARCH_HAS_DEBUG_WX
 	select ARCH_BINFMT_ELF_STATE
 	select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION

arch/arm64/include/asm/atomic.h

@@ -223,6 +223,4 @@ static __always_inline long arch_atomic64_dec_if_positive(atomic64_t *v)
 
 #define arch_atomic64_dec_if_positive		arch_atomic64_dec_if_positive
 
-#define ARCH_ATOMIC
-
 #endif /* __ASM_ATOMIC_H */

arch/s390/Kconfig

@@ -58,6 +58,7 @@ config S390
 	# Note: keep this list sorted alphabetically
 	#
 	imply IMA_SECURE_AND_OR_TRUSTED_BOOT
+	select ARCH_ATOMIC
 	select ARCH_32BIT_USTAT_F_TINODE
 	select ARCH_BINFMT_ELF_STATE
 	select ARCH_ENABLE_MEMORY_HOTPLUG if SPARSEMEM

arch/s390/include/asm/atomic.h

@@ -147,6 +147,4 @@ ATOMIC64_OPS(xor)
 #define arch_atomic64_fetch_sub(_i, _v)  arch_atomic64_fetch_add(-(s64)(_i), _v)
 #define arch_atomic64_sub(_i, _v)	 arch_atomic64_add(-(s64)(_i), _v)
 
-#define ARCH_ATOMIC
-
 #endif /* __ARCH_S390_ATOMIC__  */

arch/um/Kconfig

@@ -5,6 +5,7 @@ menu "UML-specific options"
 config UML
 	bool
 	default y
+	select ARCH_ATOMIC
 	select ARCH_EPHEMERAL_INODES
 	select ARCH_HAS_KCOV
 	select ARCH_NO_PREEMPT

arch/x86/Kconfig

@@ -58,6 +58,7 @@ config X86
 	#
 	select ACPI_LEGACY_TABLES_LOOKUP	if ACPI
 	select ACPI_SYSTEM_POWER_STATES_SUPPORT	if ACPI
+	select ARCH_ATOMIC
 	select ARCH_32BIT_OFF_T			if X86_32
 	select ARCH_CLOCKSOURCE_INIT
 	select ARCH_ENABLE_HUGEPAGE_MIGRATION if X86_64 && HUGETLB_PAGE && MIGRATION

arch/x86/include/asm/atomic.h

@@ -269,6 +269,4 @@ static __always_inline int arch_atomic_fetch_xor(int i, atomic_t *v)
 # include <asm/atomic64_64.h>
 #endif
 
-#define ARCH_ATOMIC
-
 #endif /* _ASM_X86_ATOMIC_H */

include/linux/atomic.h

@@ -77,7 +77,7 @@
 	__ret;								\
 })
 
-#ifdef ARCH_ATOMIC
+#ifdef CONFIG_ARCH_ATOMIC
 #include <linux/atomic-arch-fallback.h>
 #include <asm-generic/atomic-instrumented.h>
 #else