[PATCH v2 12/33] locking/atomic: cmpxchg: support ARCH_ATOMIC

From: Mark Rutland
Date: Tue May 25 2021 - 10:05:39 EST

We'd like all architectures to convert to ARCH_ATOMIC, as this will
enable functionality, and once all architectures are converted it will
be possible to make significant cleanups to the atomic headers.

A number of architectures use asm-generic/cmpxchg.h or
asm-generic/cmpxhg-local.h, and it's impractical to convert the headers
and all these architectures in one go. To make it possible to convert
them one-by-one, let's make the asm-generic implementation function as
either cmpxchg*() or arch_cmpxchg*() depending on whether ARCH_ATOMIC is
selected. To do this, the generic implementations are prefixed as
generic_cmpxchg_*(), and preprocessor definitions map
cmpxchg_*()/arch_cmpxchg_*() onto these as appropriate.

Once all users are moved over to ARCH_ATOMIC the ifdeffery in the header
can be simplified and/or removed entirely.

For existing users (none of which select ARCH_ATOMIC), there should be
no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
include/asm-generic/cmpxchg.h | 61 +++++++++++++++++++++++++++++++------------
1 file changed, 44 insertions(+), 17 deletions(-)

diff --git a/include/asm-generic/cmpxchg.h b/include/asm-generic/cmpxchg.h
index b9d54c7afc52..98c931199089 100644
--- a/include/asm-generic/cmpxchg.h
+++ b/include/asm-generic/cmpxchg.h
@@ -14,16 +14,14 @@
#include <linux/types.h>
#include <linux/irqflags.h>

-#ifndef xchg
* This function doesn't exist, so you'll get a linker error if
* something tries to do an invalidly-sized xchg().
-extern void __xchg_called_with_bad_pointer(void);
+extern void __generic_xchg_called_with_bad_pointer(void);

static inline
-unsigned long __xchg(unsigned long x, volatile void *ptr, int size)
+unsigned long __generic_xchg(unsigned long x, volatile void *ptr, int size)
unsigned long ret, flags;

@@ -75,35 +73,64 @@ unsigned long __xchg(unsigned long x, volatile void *ptr, int size)
#endif /* CONFIG_64BIT */

- __xchg_called_with_bad_pointer();
+ __generic_xchg_called_with_bad_pointer();
return x;

-#define xchg(ptr, x) ({ \
- ((__typeof__(*(ptr))) \
- __xchg((unsigned long)(x), (ptr), sizeof(*(ptr)))); \
+#define generic_xchg(ptr, x) ({ \
+ ((__typeof__(*(ptr))) \
+ __generic_xchg((unsigned long)(x), (ptr), sizeof(*(ptr)))); \

-#endif /* xchg */
* Atomic compare and exchange.
#include <asm-generic/cmpxchg-local.h>

-#ifndef cmpxchg_local
-#define cmpxchg_local(ptr, o, n) ({ \
- ((__typeof__(*(ptr)))__generic_cmpxchg_local((ptr), (unsigned long)(o),\
- (unsigned long)(n), sizeof(*(ptr)))); \
+#define generic_cmpxchg_local(ptr, o, n) ({ \
+ ((__typeof__(*(ptr)))__generic_cmpxchg_local((ptr), (unsigned long)(o), \
+ (unsigned long)(n), sizeof(*(ptr)))); \
+#define generic_cmpxchg64_local(ptr, o, n) \
+ __generic_cmpxchg64_local((ptr), (o), (n))
+#ifndef arch_xchg
+#define arch_xchg generic_xchg
+#ifndef arch_cmpxchg_local
+#define arch_cmpxchg_local generic_cmpxchg_local
+#ifndef arch_cmpxchg64_local
+#define arch_cmpxchg64_local generic_cmpxchg64_local
+#define arch_cmpxchg arch_cmpxchg_local
+#define arch_cmpxchg64 arch_cmpxchg64_local
+#ifndef xchg
+#define xchg generic_xchg
+#ifndef cmpxchg_local
+#define cmpxchg_local generic_cmpxchg_local

#ifndef cmpxchg64_local
-#define cmpxchg64_local(ptr, o, n) __generic_cmpxchg64_local((ptr), (o), (n))
+#define cmpxchg64_local generic_cmpxchg64_local

-#define cmpxchg(ptr, o, n) cmpxchg_local((ptr), (o), (n))
-#define cmpxchg64(ptr, o, n) cmpxchg64_local((ptr), (o), (n))
+#define cmpxchg cmpxchg_local
+#define cmpxchg64 cmpxchg64_local
+#endif /* CONFIG_ARCH_ATOMIC */

#endif /* __ASM_GENERIC_CMPXCHG_H */