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Commit 4a6dae6d authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

[PATCH] atomic: cmpxchg 



Introduce an atomic_cmpxchg operation.

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 53e86b91

Documentation/atomic_ops.txt

+15 −0
Original line number Diff line number Diff line
@@ -115,6 +115,21 @@ boolean is return which indicates whether the resulting counter value 
is negative.  It requires explicit memory barrier semantics around the

operation.



Finally:



	int atomic_cmpxchg(atomic_t *v, int old, int new);



This performs an atomic compare exchange operation on the atomic value v,

with the given old and new values. Like all atomic_xxx operations,

atomic_cmpxchg will only satisfy its atomicity semantics as long as all

other accesses of *v are performed through atomic_xxx operations.



atomic_cmpxchg requires explicit memory barriers around the operation.



The semantics for atomic_cmpxchg are the same as those defined for 'cas'

below.





If a caller requires memory barrier semantics around an atomic_t

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

defined which accomplish this:

arch/sparc/lib/atomic32.c

+16 −5
Original line number Diff line number Diff line
@@ -37,17 +37,28 @@ int __atomic_add_return(int i, atomic_t *v) 
	spin_unlock_irqrestore(ATOMIC_HASH(v), flags);

	return ret;

}

EXPORT_SYMBOL(__atomic_add_return);



void atomic_set(atomic_t *v, int i)

int atomic_cmpxchg(atomic_t *v, int old, int new)

{

	int ret;

	unsigned long flags;

	spin_lock_irqsave(ATOMIC_HASH(v), flags);



	v->counter = i;

	spin_lock_irqsave(ATOMIC_HASH(v), flags);

	ret = v->counter;

	if (likely(ret == old))

		v->counter = new;



	spin_unlock_irqrestore(ATOMIC_HASH(v), flags);

	return ret;

}



EXPORT_SYMBOL(__atomic_add_return);

EXPORT_SYMBOL(atomic_set);

void atomic_set(atomic_t *v, int i)

{

	unsigned long flags;



	spin_lock_irqsave(ATOMIC_HASH(v), flags);

	v->counter = i;

	spin_unlock_irqrestore(ATOMIC_HASH(v), flags);

}

EXPORT_SYMBOL(atomic_set);

include/asm-alpha/atomic.h

+2 −0
Original line number Diff line number Diff line
@@ -177,6 +177,8 @@ static __inline__ long atomic64_sub_return(long i, atomic64_t * v) 
	return result;

}



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



#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

+31 −0
Original line number Diff line number Diff line
@@ -80,6 +80,23 @@ static inline int atomic_sub_return(int i, atomic_t *v) 
	return result;

}



static inline int atomic_cmpxchg(atomic_t *ptr, int old, int new)

{

	u32 oldval, res;



	do {

		__asm__ __volatile__("@ atomic_cmpxchg\n"

		"ldrex	%1, [%2]\n"

		"teq	%1, %3\n"

		"strexeq %0, %4, [%2]\n"

		    : "=&r" (res), "=&r" (oldval)

		    : "r" (&ptr->counter), "Ir" (old), "r" (new)

		    : "cc");

	} while (res);



	return oldval;

}



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

{

	unsigned long tmp, tmp2;
@@ -131,6 +148,20 @@ static inline int atomic_sub_return(int i, atomic_t *v) 
	return val;

}



static inline int atomic_cmpxchg(atomic_t *v, int old, int new)

{

	int ret;

	unsigned long flags;



	local_irq_save(flags);

	ret = v->counter;

	if (likely(ret == old))

		v->counter = new;

	local_irq_restore(flags);



	return ret;

}



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

{

	unsigned long flags;

include/asm-arm26/atomic.h

+14 −0
Original line number Diff line number Diff line
@@ -62,6 +62,20 @@ static inline int atomic_sub_return(int i, atomic_t *v) 
        return val;

}



static inline int atomic_cmpxchg(atomic_t *v, int old, int new)

{

	int ret;

	unsigned long flags;



	local_irq_save(flags);

	ret = v->counter;

	if (likely(ret == old))

		v->counter = new;

	local_irq_restore(flags);



	return ret;

}



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

{

        unsigned long flags;