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Commit 8426e1f6 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

[PATCH] atomic: inc_not_zero 



Introduce an atomic_inc_not_zero operation.  Make this a special case of
atomic_add_unless because lockless pagecache actually wants
atomic_inc_not_negativeone due to its offset refcount.

Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 4a6dae6d

Documentation/atomic_ops.txt

+13 −1
Original line number Diff line number Diff line
@@ -115,7 +115,7 @@ boolean is return which indicates whether the resulting counter value 
is negative.  It requires explicit memory barrier semantics around the

operation.



Finally:

Then:



	int atomic_cmpxchg(atomic_t *v, int old, int new);
@@ -129,6 +129,18 @@ atomic_cmpxchg requires explicit memory barriers around the operation. 
The semantics for atomic_cmpxchg are the same as those defined for 'cas'

below.



Finally:



	int atomic_add_unless(atomic_t *v, int a, int u);



If the atomic value v is not equal to u, this function adds a to v, and

returns non zero. If v is equal to u then it returns zero. This is done as

an atomic operation.



atomic_add_unless requires explicit memory barriers around the operation.



atomic_inc_not_zero, equivalent to atomic_add_unless(v, 1, 0)





If a caller requires memory barrier semantics around an atomic_t

operation which does not return a value, a set of interfaces are

arch/sparc/lib/atomic32.c

+15 −0
Original line number Diff line number Diff line
@@ -53,6 +53,21 @@ int atomic_cmpxchg(atomic_t *v, int old, int new) 
	return ret;

}



int atomic_add_unless(atomic_t *v, int a, int u)

{

	int ret;

	unsigned long flags;



	spin_lock_irqsave(ATOMIC_HASH(v), flags);

	ret = v->counter;

	if (ret != u)

		v->counter += a;

	spin_unlock_irqrestore(ATOMIC_HASH(v), flags);

	return ret != u;

}



static inline void atomic_clear_mask(unsigned long mask, unsigned long *addr)

/* Atomic operations are already serializing */

void atomic_set(atomic_t *v, int i)

{

	unsigned long flags;

include/asm-alpha/atomic.h

+10 −0
Original line number Diff line number Diff line
@@ -179,6 +179,16 @@ static __inline__ long atomic64_sub_return(long i, atomic64_t * v) 


#define atomic_cmpxchg(v, o, n) ((int)cmpxchg(&((v)->counter), (o), (n)))



#define atomic_add_unless(v, a, u)				\

({								\

	int c, old;						\

	c = atomic_read(v);					\

	while (c != (u) && (old = atomic_cmpxchg((v), c, c + (a))) != c) \

		c = old;					\

	c != (u);						\

})

#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)



#define atomic_dec_return(v) atomic_sub_return(1,(v))

#define atomic64_dec_return(v) atomic64_sub_return(1,(v))

include/asm-arm/atomic.h

+11 −0
Original line number Diff line number Diff line
@@ -173,6 +173,17 @@ static inline void atomic_clear_mask(unsigned long mask, unsigned long *addr) 


#endif /* __LINUX_ARM_ARCH__ */



static inline int atomic_add_unless(atomic_t *v, int a, int u)

{

	int c, old;



	c = atomic_read(v);

	while (c != u && (old = atomic_cmpxchg((v), c, c + a)) != c)

		c = old;

	return c != u;

}

#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)



#define atomic_add(i, v)	(void) atomic_add_return(i, v)

#define atomic_inc(v)		(void) atomic_add_return(1, v)

#define atomic_sub(i, v)	(void) atomic_sub_return(i, v)

include/asm-arm26/atomic.h

+15 −0
Original line number Diff line number Diff line
@@ -76,6 +76,21 @@ static inline int atomic_cmpxchg(atomic_t *v, int old, int new) 
	return ret;

}



static inline int atomic_add_unless(atomic_t *v, int a, int u)

{

	int ret;

	unsigned long flags;



	local_irq_save(flags);

	ret = v->counter;

	if (ret != u)

		v->counter += a;

	local_irq_restore(flags);



	return ret != u;

}

#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)



static inline void atomic_clear_mask(unsigned long mask, unsigned long *addr)

{

        unsigned long flags;