[PATCH] asm-generic: atomic64: handle ARCH_ATOMIC builds (was "Re: [PATCH v3 1/2] locking/atomics: Fixup GENERIC_ATOMIC64 conflict") with atomic-arch-fallback.h

Mark Rutland mark.rutland at arm.com
Thu Apr 22 11:59:45 BST 2021

Hi Guo,

On Wed, Apr 21, 2021 at 12:53:45PM +0000, guoren at kernel.org wrote:
> From: Guo Ren <guoren at linux.alibaba.com>
> Current GENERIC_ATOMIC64 in atomic-arch-fallback.h is broken. When a 32-bit
> arch use atomic-arch-fallback.h will cause compile error.
> In file included from include/linux/atomic.h:81,
>                     from include/linux/rcupdate.h:25,
>                     from include/linux/rculist.h:11,
>                     from include/linux/pid.h:5,
>                     from include/linux/sched.h:14,
>                     from arch/riscv/kernel/asm-offsets.c:10:
>    include/linux/atomic-arch-fallback.h: In function 'arch_atomic64_inc':
> >> include/linux/atomic-arch-fallback.h:1447:2: error: implicit declaration of function 'arch_atomic64_add'; did you mean 'arch_atomic_add'? [-Werror=implicit-function-declaration]
>     1447 |  arch_atomic64_add(1, v);
>          |  ^~~~~~~~~~~~~~~~~
>          |  arch_atomic_add

This is expected; GENERIC_ATOMIC64 doesn't implement arch_atomic64_*(),
and thus violates the expectations of the fallback code.

To make GENERIC_ATOMIC64 compatible with ARCH_ATOMIC, the
GENERIC_ATOMIC64 implementation *must* provide arch_atomic64_*()

> The atomic-arch-fallback.h & atomic-fallback.h &
> atomic-instrumented.h are generated by gen-atomic-fallback.sh &
> gen-atomic-instrumented.sh, so just take care the bash files.
> Remove the dependency of atomic-*-fallback.h in atomic64.h.

Please don't duplicate the fallbacks; this'll make it harder to move
other over and eventually remove the non-ARCH_ATOMIC implementations.

Does the patch below make things work for you, or have I missed

I've given this a basic build test on an arm config using

>From 7f0389c8a1f41ecb5b2700f6ba38ff2ba093eb33 Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland at arm.com>
Date: Thu, 22 Apr 2021 11:26:04 +0100
Subject: [PATCH] asm-generic: atomic64: handle ARCH_ATOMIC builds

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 GENERIC_ATOMIC64, and it's impractical to
convert them all in one go. To make it possible to convert them
one-by-one, let's make the GENERIC_ATOMIC64 implementation function as
either atomic64_*() or arch_atomic64_*() depending on whether
ARCH_ATOMIC is selected. To do this, the C implementations are prefixed
as generic_atomic64_*(), and the asm-generic/atomic64.h header maps
atomic64_*()/arch_atomic64_*() onto these as appropriate via teh

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 at arm.com>
Cc: Arnd Bergmann <arnd at arndb.de>
Cc: Guo Ren <guoren at linux.alibaba.com>
Cc: Peter Zijlstra <peterz at infradead.org>
 include/asm-generic/atomic64.h | 74 ++++++++++++++++++++++++++++++++++--------
 lib/atomic64.c                 | 36 ++++++++++----------
 2 files changed, 79 insertions(+), 31 deletions(-)

diff --git a/include/asm-generic/atomic64.h b/include/asm-generic/atomic64.h
index 370f01d4450f..45c7ff8c9477 100644
--- a/include/asm-generic/atomic64.h
+++ b/include/asm-generic/atomic64.h
@@ -15,19 +15,17 @@ typedef struct {
 #define ATOMIC64_INIT(i)	{ (i) }
-extern s64 atomic64_read(const atomic64_t *v);
-extern void atomic64_set(atomic64_t *v, s64 i);
-#define atomic64_set_release(v, i)	atomic64_set((v), (i))
+extern s64 generic_atomic64_read(const atomic64_t *v);
+extern void generic_atomic64_set(atomic64_t *v, s64 i);
 #define ATOMIC64_OP(op)							\
-extern void	 atomic64_##op(s64 a, atomic64_t *v);
+extern void generic_atomic64_##op(s64 a, atomic64_t *v);
 #define ATOMIC64_OP_RETURN(op)						\
-extern s64 atomic64_##op##_return(s64 a, atomic64_t *v);
+extern s64 generic_atomic64_##op##_return(s64 a, atomic64_t *v);
 #define ATOMIC64_FETCH_OP(op)						\
-extern s64 atomic64_fetch_##op(s64 a, atomic64_t *v);
+extern s64 generic_atomic64_fetch_##op(s64 a, atomic64_t *v);
@@ -46,11 +44,61 @@ ATOMIC64_OPS(xor)
 #undef ATOMIC64_OP
-extern s64 atomic64_dec_if_positive(atomic64_t *v);
-#define atomic64_dec_if_positive atomic64_dec_if_positive
-extern s64 atomic64_cmpxchg(atomic64_t *v, s64 o, s64 n);
-extern s64 atomic64_xchg(atomic64_t *v, s64 new);
-extern s64 atomic64_fetch_add_unless(atomic64_t *v, s64 a, s64 u);
-#define atomic64_fetch_add_unless atomic64_fetch_add_unless
+extern s64 generic_atomic64_dec_if_positive(atomic64_t *v);
+extern s64 generic_atomic64_cmpxchg(atomic64_t *v, s64 o, s64 n);
+extern s64 generic_atomic64_xchg(atomic64_t *v, s64 new);
+extern s64 generic_atomic64_fetch_add_unless(atomic64_t *v, s64 a, s64 u);
+#define arch_atomic64_read		generic_atomic64_read
+#define arch_atomic64_set		generic_atomic64_set
+#define arch_atomic64_set_release	generic_atomic64_set
+#define	arch_atomic64_add		generic_atomic64_add
+#define	arch_atomic64_add_return	generic_atomic64_add_return
+#define	arch_atomic64_fetch_add		generic_atomic64_fetch_add
+#define	arch_atomic64_sub		generic_atomic64_sub
+#define	arch_atomic64_sub_return	generic_atomic64_sub_return
+#define	arch_atomic64_fetch_sub		generic_atomic64_fetch_sub
+#define	arch_atomic64_and		generic_atomic64_and
+#define	arch_atomic64_fetch_and		generic_atomic64_fetch_and
+#define	arch_atomic64_or		generic_atomic64_or
+#define	arch_atomic64_fetch_or		generic_atomic64_fetch_or
+#define	arch_atomic64_xor		generic_atomic64_xor
+#define	arch_atomic64_fetch_xor		generic_atomic64_fetch_xor
+#define arch_atomic64_dec_if_positive 	generic_atomic64_dec_if_positive
+#define arch_atomic64_cmpxchg	 	generic_atomic64_cmpxchg
+#define arch_atomic64_xchg	 	generic_atomic64_xchg
+#define arch_atomic64_fetch_add_unless	generic_atomic64_fetch_add_unless
+#else /* ARCH_ATOMIC */
+#define atomic64_read			generic_atomic64_read
+#define atomic64_set			generic_atomic64_set
+#define atomic64_set_release		generic_atomic64_set
+#define	atomic64_add			generic_atomic64_add
+#define	atomic64_add_return		generic_atomic64_add_return
+#define	atomic64_fetch_add		generic_atomic64_fetch_add
+#define	atomic64_sub			generic_atomic64_sub
+#define	atomic64_sub_return		generic_atomic64_sub_return
+#define	atomic64_fetch_sub		generic_atomic64_fetch_sub
+#define	atomic64_and			generic_atomic64_and
+#define	atomic64_fetch_and		generic_atomic64_fetch_and
+#define	atomic64_or			generic_atomic64_or
+#define	atomic64_fetch_or		generic_atomic64_fetch_or
+#define	atomic64_xor			generic_atomic64_xor
+#define	atomic64_fetch_xor		generic_atomic64_fetch_xor
+#define atomic64_dec_if_positive 	generic_atomic64_dec_if_positive
+#define atomic64_cmpxchg	 	generic_atomic64_cmpxchg
+#define atomic64_xchg	 		generic_atomic64_xchg
+#define atomic64_fetch_add_unless	generic_atomic64_fetch_add_unless
+#endif /* ARCH_ATOMIC */
 #endif  /*  _ASM_GENERIC_ATOMIC64_H  */
diff --git a/lib/atomic64.c b/lib/atomic64.c
index e98c85a99787..3df653994177 100644
--- a/lib/atomic64.c
+++ b/lib/atomic64.c
@@ -42,7 +42,7 @@ static inline raw_spinlock_t *lock_addr(const atomic64_t *v)
 	return &atomic64_lock[addr & (NR_LOCKS - 1)].lock;
-s64 atomic64_read(const atomic64_t *v)
+s64 generic_atomic64_read(const atomic64_t *v)
 	unsigned long flags;
 	raw_spinlock_t *lock = lock_addr(v);
@@ -53,9 +53,9 @@ s64 atomic64_read(const atomic64_t *v)
 	raw_spin_unlock_irqrestore(lock, flags);
 	return val;
-void atomic64_set(atomic64_t *v, s64 i)
+void generic_atomic64_set(atomic64_t *v, s64 i)
 	unsigned long flags;
 	raw_spinlock_t *lock = lock_addr(v);
@@ -64,10 +64,10 @@ void atomic64_set(atomic64_t *v, s64 i)
 	v->counter = i;
 	raw_spin_unlock_irqrestore(lock, flags);
 #define ATOMIC64_OP(op, c_op)						\
-void atomic64_##op(s64 a, atomic64_t *v)				\
+void generic_atomic64_##op(s64 a, atomic64_t *v)			\
 {									\
 	unsigned long flags;						\
 	raw_spinlock_t *lock = lock_addr(v);				\
@@ -76,10 +76,10 @@ void atomic64_##op(s64 a, atomic64_t *v)				\
 	v->counter c_op a;						\
 	raw_spin_unlock_irqrestore(lock, flags);			\
 }									\
 #define ATOMIC64_OP_RETURN(op, c_op)					\
-s64 atomic64_##op##_return(s64 a, atomic64_t *v)			\
+s64 generic_atomic64_##op##_return(s64 a, atomic64_t *v)		\
 {									\
 	unsigned long flags;						\
 	raw_spinlock_t *lock = lock_addr(v);				\
@@ -90,10 +90,10 @@ s64 atomic64_##op##_return(s64 a, atomic64_t *v)			\
 	raw_spin_unlock_irqrestore(lock, flags);			\
 	return val;							\
 }									\
 #define ATOMIC64_FETCH_OP(op, c_op)					\
-s64 atomic64_fetch_##op(s64 a, atomic64_t *v)				\
+s64 generic_atomic64_fetch_##op(s64 a, atomic64_t *v)			\
 {									\
 	unsigned long flags;						\
 	raw_spinlock_t *lock = lock_addr(v);				\
@@ -105,7 +105,7 @@ s64 atomic64_fetch_##op(s64 a, atomic64_t *v)				\
 	raw_spin_unlock_irqrestore(lock, flags);			\
 	return val;							\
 }									\
 #define ATOMIC64_OPS(op, c_op)						\
 	ATOMIC64_OP(op, c_op)						\
@@ -130,7 +130,7 @@ ATOMIC64_OPS(xor, ^=)
 #undef ATOMIC64_OP
-s64 atomic64_dec_if_positive(atomic64_t *v)
+s64 generic_atomic64_dec_if_positive(atomic64_t *v)
 	unsigned long flags;
 	raw_spinlock_t *lock = lock_addr(v);
@@ -143,9 +143,9 @@ s64 atomic64_dec_if_positive(atomic64_t *v)
 	raw_spin_unlock_irqrestore(lock, flags);
 	return val;
-s64 atomic64_cmpxchg(atomic64_t *v, s64 o, s64 n)
+s64 generic_atomic64_cmpxchg(atomic64_t *v, s64 o, s64 n)
 	unsigned long flags;
 	raw_spinlock_t *lock = lock_addr(v);
@@ -158,9 +158,9 @@ s64 atomic64_cmpxchg(atomic64_t *v, s64 o, s64 n)
 	raw_spin_unlock_irqrestore(lock, flags);
 	return val;
-s64 atomic64_xchg(atomic64_t *v, s64 new)
+s64 generic_atomic64_xchg(atomic64_t *v, s64 new)
 	unsigned long flags;
 	raw_spinlock_t *lock = lock_addr(v);
@@ -172,9 +172,9 @@ s64 atomic64_xchg(atomic64_t *v, s64 new)
 	raw_spin_unlock_irqrestore(lock, flags);
 	return val;
-s64 atomic64_fetch_add_unless(atomic64_t *v, s64 a, s64 u)
+s64 generic_atomic64_fetch_add_unless(atomic64_t *v, s64 a, s64 u)
 	unsigned long flags;
 	raw_spinlock_t *lock = lock_addr(v);
@@ -188,4 +188,4 @@ s64 atomic64_fetch_add_unless(atomic64_t *v, s64 a, s64 u)
 	return val;

More information about the linux-riscv mailing list