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linux_dsm_epyc7002/include/linux/atomic.h
Will Deacon 654672d4ba locking/atomics: Add _{acquire|release|relaxed}() variants of some atomic operations 
Whilst porting the generic qrwlock code over to arm64, it became
apparent that any portable locking code needs finer-grained control of
the memory-ordering guarantees provided by our atomic routines.

In particular: xchg, cmpxchg, {add,sub}_return are often used in
situations where full barrier semantics (currently the only option
available) are not required. For example, when a reader increments a
reader count to obtain a lock, checking the old value to see if a writer
was present, only acquire semantics are strictly needed.

This patch introduces three new ordering semantics for these operations:

  - *_relaxed: No ordering guarantees. This is similar to what we have
               already for the non-return atomics (e.g. atomic_add).

  - *_acquire: ACQUIRE semantics, similar to smp_load_acquire.

  - *_release: RELEASE semantics, similar to smp_store_release.

In memory-ordering speak, this means that the acquire/release semantics
are RCpc as opposed to RCsc. Consequently a RELEASE followed by an
ACQUIRE does not imply a full barrier, as already documented in
memory-barriers.txt.

Currently, all the new macros are conditionally mapped to the full-mb
variants, however if the *_relaxed version is provided by the
architecture, then the acquire/release variants are constructed by
supplementing the relaxed routine with an explicit barrier.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman.Long@hp.com
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1438880084-18856-2-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-08-12 11:58:59 +02:00

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/* Atomic operations usable in machine independent code */
#ifndef _LINUX_ATOMIC_H
#define _LINUX_ATOMIC_H
#include <asm/atomic.h>
#include <asm/barrier.h>
/*
* Relaxed variants of xchg, cmpxchg and some atomic operations.
*
* We support four variants:
*
* - Fully ordered: The default implementation, no suffix required.
* - Acquire: Provides ACQUIRE semantics, _acquire suffix.
* - Release: Provides RELEASE semantics, _release suffix.
* - Relaxed: No ordering guarantees, _relaxed suffix.
*
* For compound atomics performing both a load and a store, ACQUIRE
* semantics apply only to the load and RELEASE semantics only to the
* store portion of the operation. Note that a failed cmpxchg_acquire
* does -not- imply any memory ordering constraints.
*
* See Documentation/memory-barriers.txt for ACQUIRE/RELEASE definitions.
*/
#ifndef atomic_read_acquire
#define atomic_read_acquire(v) smp_load_acquire(&(v)->counter)
#endif
#ifndef atomic_set_release
#define atomic_set_release(v, i) smp_store_release(&(v)->counter, (i))
#endif
/*
* The idea here is to build acquire/release variants by adding explicit
* barriers on top of the relaxed variant. In the case where the relaxed
* variant is already fully ordered, no additional barriers are needed.
*/
#define __atomic_op_acquire(op, args...) \
({ \
typeof(op##_relaxed(args)) __ret = op##_relaxed(args); \
smp_mb__after_atomic(); \
__ret; \
})
#define __atomic_op_release(op, args...) \
({ \
smp_mb__before_atomic(); \
op##_relaxed(args); \
})
#define __atomic_op_fence(op, args...) \
({ \
typeof(op##_relaxed(args)) __ret; \
smp_mb__before_atomic(); \
__ret = op##_relaxed(args); \
smp_mb__after_atomic(); \
__ret; \
})
/* atomic_add_return_relaxed */
#ifndef atomic_add_return_relaxed
#define atomic_add_return_relaxed atomic_add_return
#define atomic_add_return_acquire atomic_add_return
#define atomic_add_return_release atomic_add_return
#else /* atomic_add_return_relaxed */
#ifndef atomic_add_return_acquire
#define atomic_add_return_acquire(...) \
__atomic_op_acquire(atomic_add_return, __VA_ARGS__)
#endif
#ifndef atomic_add_return_release
#define atomic_add_return_release(...) \
__atomic_op_release(atomic_add_return, __VA_ARGS__)
#endif
#ifndef atomic_add_return
#define atomic_add_return(...) \
__atomic_op_fence(atomic_add_return, __VA_ARGS__)
#endif
#endif /* atomic_add_return_relaxed */
/* atomic_sub_return_relaxed */
#ifndef atomic_sub_return_relaxed
#define atomic_sub_return_relaxed atomic_sub_return
#define atomic_sub_return_acquire atomic_sub_return
#define atomic_sub_return_release atomic_sub_return
#else /* atomic_sub_return_relaxed */
#ifndef atomic_sub_return_acquire
#define atomic_sub_return_acquire(...) \
__atomic_op_acquire(atomic_sub_return, __VA_ARGS__)
#endif
#ifndef atomic_sub_return_release
#define atomic_sub_return_release(...) \
__atomic_op_release(atomic_sub_return, __VA_ARGS__)
#endif
#ifndef atomic_sub_return
#define atomic_sub_return(...) \
__atomic_op_fence(atomic_sub_return, __VA_ARGS__)
#endif
#endif /* atomic_sub_return_relaxed */
/* atomic_xchg_relaxed */
#ifndef atomic_xchg_relaxed
#define atomic_xchg_relaxed atomic_xchg
#define atomic_xchg_acquire atomic_xchg
#define atomic_xchg_release atomic_xchg
#else /* atomic_xchg_relaxed */
#ifndef atomic_xchg_acquire
#define atomic_xchg_acquire(...) \
__atomic_op_acquire(atomic_xchg, __VA_ARGS__)
#endif
#ifndef atomic_xchg_release
#define atomic_xchg_release(...) \
__atomic_op_release(atomic_xchg, __VA_ARGS__)
#endif
#ifndef atomic_xchg
#define atomic_xchg(...) \
__atomic_op_fence(atomic_xchg, __VA_ARGS__)
#endif
#endif /* atomic_xchg_relaxed */
/* atomic_cmpxchg_relaxed */
#ifndef atomic_cmpxchg_relaxed
#define atomic_cmpxchg_relaxed atomic_cmpxchg
#define atomic_cmpxchg_acquire atomic_cmpxchg
#define atomic_cmpxchg_release atomic_cmpxchg
#else /* atomic_cmpxchg_relaxed */
#ifndef atomic_cmpxchg_acquire
#define atomic_cmpxchg_acquire(...) \
__atomic_op_acquire(atomic_cmpxchg, __VA_ARGS__)
#endif
#ifndef atomic_cmpxchg_release
#define atomic_cmpxchg_release(...) \
__atomic_op_release(atomic_cmpxchg, __VA_ARGS__)
#endif
#ifndef atomic_cmpxchg
#define atomic_cmpxchg(...) \
__atomic_op_fence(atomic_cmpxchg, __VA_ARGS__)
#endif
#endif /* atomic_cmpxchg_relaxed */
#ifndef atomic64_read_acquire
#define atomic64_read_acquire(v) smp_load_acquire(&(v)->counter)
#endif
#ifndef atomic64_set_release
#define atomic64_set_release(v, i) smp_store_release(&(v)->counter, (i))
#endif
/* atomic64_add_return_relaxed */
#ifndef atomic64_add_return_relaxed
#define atomic64_add_return_relaxed atomic64_add_return
#define atomic64_add_return_acquire atomic64_add_return
#define atomic64_add_return_release atomic64_add_return
#else /* atomic64_add_return_relaxed */
#ifndef atomic64_add_return_acquire
#define atomic64_add_return_acquire(...) \
__atomic_op_acquire(atomic64_add_return, __VA_ARGS__)
#endif
#ifndef atomic64_add_return_release
#define atomic64_add_return_release(...) \
__atomic_op_release(atomic64_add_return, __VA_ARGS__)
#endif
#ifndef atomic64_add_return
#define atomic64_add_return(...) \
__atomic_op_fence(atomic64_add_return, __VA_ARGS__)
#endif
#endif /* atomic64_add_return_relaxed */
/* atomic64_sub_return_relaxed */
#ifndef atomic64_sub_return_relaxed
#define atomic64_sub_return_relaxed atomic64_sub_return
#define atomic64_sub_return_acquire atomic64_sub_return
#define atomic64_sub_return_release atomic64_sub_return
#else /* atomic64_sub_return_relaxed */
#ifndef atomic64_sub_return_acquire
#define atomic64_sub_return_acquire(...) \
__atomic_op_acquire(atomic64_sub_return, __VA_ARGS__)
#endif
#ifndef atomic64_sub_return_release
#define atomic64_sub_return_release(...) \
__atomic_op_release(atomic64_sub_return, __VA_ARGS__)
#endif
#ifndef atomic64_sub_return
#define atomic64_sub_return(...) \
__atomic_op_fence(atomic64_sub_return, __VA_ARGS__)
#endif
#endif /* atomic64_sub_return_relaxed */
/* atomic64_xchg_relaxed */
#ifndef atomic64_xchg_relaxed
#define atomic64_xchg_relaxed atomic64_xchg
#define atomic64_xchg_acquire atomic64_xchg
#define atomic64_xchg_release atomic64_xchg
#else /* atomic64_xchg_relaxed */
#ifndef atomic64_xchg_acquire
#define atomic64_xchg_acquire(...) \
__atomic_op_acquire(atomic64_xchg, __VA_ARGS__)
#endif
#ifndef atomic64_xchg_release
#define atomic64_xchg_release(...) \
__atomic_op_release(atomic64_xchg, __VA_ARGS__)
#endif
#ifndef atomic64_xchg
#define atomic64_xchg(...) \
__atomic_op_fence(atomic64_xchg, __VA_ARGS__)
#endif
#endif /* atomic64_xchg_relaxed */
/* atomic64_cmpxchg_relaxed */
#ifndef atomic64_cmpxchg_relaxed
#define atomic64_cmpxchg_relaxed atomic64_cmpxchg
#define atomic64_cmpxchg_acquire atomic64_cmpxchg
#define atomic64_cmpxchg_release atomic64_cmpxchg
#else /* atomic64_cmpxchg_relaxed */
#ifndef atomic64_cmpxchg_acquire
#define atomic64_cmpxchg_acquire(...) \
__atomic_op_acquire(atomic64_cmpxchg, __VA_ARGS__)
#endif
#ifndef atomic64_cmpxchg_release
#define atomic64_cmpxchg_release(...) \
__atomic_op_release(atomic64_cmpxchg, __VA_ARGS__)
#endif
#ifndef atomic64_cmpxchg
#define atomic64_cmpxchg(...) \
__atomic_op_fence(atomic64_cmpxchg, __VA_ARGS__)
#endif
#endif /* atomic64_cmpxchg_relaxed */
/* cmpxchg_relaxed */
#ifndef cmpxchg_relaxed
#define cmpxchg_relaxed cmpxchg
#define cmpxchg_acquire cmpxchg
#define cmpxchg_release cmpxchg
#else /* cmpxchg_relaxed */
#ifndef cmpxchg_acquire
#define cmpxchg_acquire(...) \
__atomic_op_acquire(cmpxchg, __VA_ARGS__)
#endif
#ifndef cmpxchg_release
#define cmpxchg_release(...) \
__atomic_op_release(cmpxchg, __VA_ARGS__)
#endif
#ifndef cmpxchg
#define cmpxchg(...) \
__atomic_op_fence(cmpxchg, __VA_ARGS__)
#endif
#endif /* cmpxchg_relaxed */
/* cmpxchg64_relaxed */
#ifndef cmpxchg64_relaxed
#define cmpxchg64_relaxed cmpxchg64
#define cmpxchg64_acquire cmpxchg64
#define cmpxchg64_release cmpxchg64
#else /* cmpxchg64_relaxed */
#ifndef cmpxchg64_acquire
#define cmpxchg64_acquire(...) \
__atomic_op_acquire(cmpxchg64, __VA_ARGS__)
#endif
#ifndef cmpxchg64_release
#define cmpxchg64_release(...) \
__atomic_op_release(cmpxchg64, __VA_ARGS__)
#endif
#ifndef cmpxchg64
#define cmpxchg64(...) \
__atomic_op_fence(cmpxchg64, __VA_ARGS__)
#endif
#endif /* cmpxchg64_relaxed */
/* xchg_relaxed */
#ifndef xchg_relaxed
#define xchg_relaxed xchg
#define xchg_acquire xchg
#define xchg_release xchg
#else /* xchg_relaxed */
#ifndef xchg_acquire
#define xchg_acquire(...) __atomic_op_acquire(xchg, __VA_ARGS__)
#endif
#ifndef xchg_release
#define xchg_release(...) __atomic_op_release(xchg, __VA_ARGS__)
#endif
#ifndef xchg
#define xchg(...) __atomic_op_fence(xchg, __VA_ARGS__)
#endif
#endif /* xchg_relaxed */
/**
* atomic_add_unless - add unless the number is already a given value
* @v: pointer of type atomic_t
* @a: the amount to add to v...
* @u: ...unless v is equal to u.
*
* Atomically adds @a to @v, so long as @v was not already @u.
* Returns non-zero if @v was not @u, and zero otherwise.
*/
static inline int atomic_add_unless(atomic_t *v, int a, int u)
{
return __atomic_add_unless(v, a, u) != u;
}
/**
* atomic_inc_not_zero - increment unless the number is zero
* @v: pointer of type atomic_t
*
* Atomically increments @v by 1, so long as @v is non-zero.
* Returns non-zero if @v was non-zero, and zero otherwise.
*/
#ifndef atomic_inc_not_zero
#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)
#endif
#ifndef atomic_andnot
static inline void atomic_andnot(int i, atomic_t *v)
{
atomic_and(~i, v);
}
#endif
static inline __deprecated void atomic_clear_mask(unsigned int mask, atomic_t *v)
{
atomic_andnot(mask, v);
}
static inline __deprecated void atomic_set_mask(unsigned int mask, atomic_t *v)
{
atomic_or(mask, v);
}
/**
* atomic_inc_not_zero_hint - increment if not null
* @v: pointer of type atomic_t
* @hint: probable value of the atomic before the increment
*
* This version of atomic_inc_not_zero() gives a hint of probable
* value of the atomic. This helps processor to not read the memory
* before doing the atomic read/modify/write cycle, lowering
* number of bus transactions on some arches.
*
* Returns: 0 if increment was not done, 1 otherwise.
*/
#ifndef atomic_inc_not_zero_hint
static inline int atomic_inc_not_zero_hint(atomic_t *v, int hint)
{
int val, c = hint;
/* sanity test, should be removed by compiler if hint is a constant */
if (!hint)
return atomic_inc_not_zero(v);
do {
val = atomic_cmpxchg(v, c, c + 1);
if (val == c)
return 1;
c = val;
} while (c);
return 0;
}
#endif
#ifndef atomic_inc_unless_negative
static inline int atomic_inc_unless_negative(atomic_t *p)
{
int v, v1;
for (v = 0; v >= 0; v = v1) {
v1 = atomic_cmpxchg(p, v, v + 1);
if (likely(v1 == v))
return 1;
}
return 0;
}
#endif
#ifndef atomic_dec_unless_positive
static inline int atomic_dec_unless_positive(atomic_t *p)
{
int v, v1;
for (v = 0; v <= 0; v = v1) {
v1 = atomic_cmpxchg(p, v, v - 1);
if (likely(v1 == v))
return 1;
}
return 0;
}
#endif
/*
* atomic_dec_if_positive - decrement by 1 if old value positive
* @v: pointer of type atomic_t
*
* The function returns the old value of *v minus 1, even if
* the atomic variable, v, was not decremented.
*/
#ifndef atomic_dec_if_positive
static inline int atomic_dec_if_positive(atomic_t *v)
{
int c, old, dec;
c = atomic_read(v);
for (;;) {
dec = c - 1;
if (unlikely(dec < 0))
break;
old = atomic_cmpxchg((v), c, dec);
if (likely(old == c))
break;
c = old;
}
return dec;
}
#endif
#include <asm-generic/atomic-long.h>
#ifdef CONFIG_GENERIC_ATOMIC64
#include <asm-generic/atomic64.h>
#endif
#ifndef atomic64_andnot
static inline void atomic64_andnot(long long i, atomic64_t *v)
{
atomic64_and(~i, v);
}
#endif
#endif /* _LINUX_ATOMIC_H */
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