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Subject[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
Hi Guo,

On Wed, Apr 21, 2021 at 12:53:45PM +0000, wrote:
> From: Guo Ren <>
> 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 &
>, 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 <>
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 <>
Cc: Arnd Bergmann <>
Cc: Guo Ren <>
Cc: Peter Zijlstra <>
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;
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