linux/include/asm-generic/bitops/atomic.h

#ifndef _ASM_GENERIC_BITOPS_ATOMIC_H_
#define _ASM_GENERIC_BITOPS_ATOMIC_H_

#include <asm/types.h>

#define BITOP_MASK(nr)		(1UL << ((nr) % BITS_PER_LONG))
#define BITOP_WORD(nr)		((nr) / BITS_PER_LONG)

#ifdef CONFIG_SMP
#include <asm/spinlock.h>
#include <asm/cache.h>		/* we use L1_CACHE_BYTES */

/* Use an array of spinlocks for our atomic_ts.
 * Hash function to index into a different SPINLOCK.
 * Since "a" is usually an address, use one spinlock per cacheline.
 */
#  define ATOMIC_HASH_SIZE 4
#  define ATOMIC_HASH(a) (&(__atomic_hash[ (((unsigned long) a)/L1_CACHE_BYTES) & (ATOMIC_HASH_SIZE-1) ]))

extern raw_spinlock_t __atomic_hash[ATOMIC_HASH_SIZE] __lock_aligned;

/* Can't use raw_spin_lock_irq because of #include problems, so
 * this is the substitute */
#define _atomic_spin_lock_irqsave(l,f) do {	\
	raw_spinlock_t *s = ATOMIC_HASH(l);	\
	local_irq_save(f);			\
	__raw_spin_lock(s);			\
} while(0)

#define _atomic_spin_unlock_irqrestore(l,f) do {	\
	raw_spinlock_t *s = ATOMIC_HASH(l);		\
	__raw_spin_unlock(s);				\
	local_irq_restore(f);				\
} while(0)


#else
#  define _atomic_spin_lock_irqsave(l,f) do { local_irq_save(f); } while (0)
#  define _atomic_spin_unlock_irqrestore(l,f) do { local_irq_restore(f); } while (0)
#endif

/*
 * NMI events can occur at any time, including when interrupts have been
 * disabled by *_irqsave().  So you can get NMI events occurring while a
 * *_bit function is holding a spin lock.  If the NMI handler also wants
 * to do bit manipulation (and they do) then you can get a deadlock
 * between the original caller of *_bit() and the NMI handler.
 *
 * by Keith Owens
 */

/**
 * set_bit - Atomically set a bit in memory
 * @nr: the bit to set
 * @addr: the address to start counting from
 *
 * This function is atomic and may not be reordered.  See __set_bit()
 * if you do not require the atomic guarantees.
 *
 * Note: there are no guarantees that this function will not be reordered
 * on non x86 architectures, so if you are writing portable code,
 * make sure not to rely on its reordering guarantees.
 *
 * Note that @nr may be almost arbitrarily large; this function is not
 * restricted to acting on a single-word quantity.
 */
static inline void set_bit(int nr, volatile unsigned long *addr)
{
	unsigned long mask = BITOP_MASK(nr);
	unsigned long *p = ((unsigned long *)addr) + BITOP_WORD(nr);
	unsigned long flags;

	_atomic_spin_lock_irqsave(p, flags);
	*p  |= mask;
	_atomic_spin_unlock_irqrestore(p, flags);
}

/**
 * clear_bit - Clears a bit in memory
 * @nr: Bit to clear
 * @addr: Address to start counting from
 *
 * clear_bit() is atomic and may not be reordered.  However, it does
 * not contain a memory barrier, so if it is used for locking purposes,
 * you should call smp_mb__before_clear_bit() and/or smp_mb__after_clear_bit()
 * in order to ensure changes are visible on other processors.
 */
static inline void clear_bit(int nr, volatile unsigned long *addr)
{
	unsigned long mask = BITOP_MASK(nr);
	unsigned long *p = ((unsigned long *)addr) + BITOP_WORD(nr);
	unsigned long flags;

	_atomic_spin_lock_irqsave(p, flags);
	*p &= ~mask;
	_atomic_spin_unlock_irqrestore(p, flags);
}

/**
 * change_bit - Toggle a bit in memory
 * @nr: Bit to change
 * @addr: Address to start counting from
 *
 * change_bit() is atomic and may not be reordered. It may be
 * reordered on other architectures than x86.
 * Note that @nr may be almost arbitrarily large; this function is not
 * restricted to acting on a single-word quantity.
 */
static inline void change_bit(int nr, volatile unsigned long *addr)
{
	unsigned long mask = BITOP_MASK(nr);
	unsigned long *p = ((unsigned long *)addr) + BITOP_WORD(nr);
	unsigned long flags;

	_atomic_spin_lock_irqsave(p, flags);
	*p ^= mask;
	_atomic_spin_unlock_irqrestore(p, flags);
}

/**
 * test_and_set_bit - Set a bit and return its old value
 * @nr: Bit to set
 * @addr: Address to count from
 *
 * This operation is atomic and cannot be reordered.
 * It may be reordered on other architectures than x86.
 * It also implies a memory barrier.
 */
static inline int test_and_set_bit(int nr, volatile unsigned long *addr)
{
	unsigned long mask = BITOP_MASK(nr);
	unsigned long *p = ((unsigned long *)addr) + BITOP_WORD(nr);
	unsigned long old;
	unsigned long flags;

	_atomic_spin_lock_irqsave(p, flags);
	old = *p;
	*p = old | mask;
	_atomic_spin_unlock_irqrestore(p, flags);

	return (old & mask) != 0;
}

/**
 * test_and_clear_bit - Clear a bit and return its old value
 * @nr: Bit to clear
 * @addr: Address to count from
 *
 * This operation is atomic and cannot be reordered.
 * It can be reorderdered on other architectures other than x86.
 * It also implies a memory barrier.
 */
static inline int test_and_clear_bit(int nr, volatile unsigned long *addr)
{
	unsigned long mask = BITOP_MASK(nr);
	unsigned long *p = ((unsigned long *)addr) + BITOP_WORD(nr);
	unsigned long old;
	unsigned long flags;

	_atomic_spin_lock_irqsave(p, flags);
	old = *p;
	*p = old & ~mask;
	_atomic_spin_unlock_irqrestore(p, flags);

	return (old & mask) != 0;
}

/**
 * test_and_change_bit - Change a bit and return its old value
 * @nr: Bit to change
 * @addr: Address to count from
 *
 * This operation is atomic and cannot be reordered.
 * It also implies a memory barrier.
 */
static inline int test_and_change_bit(int nr, volatile unsigned long *addr)
{
	unsigned long mask = BITOP_MASK(nr);
	unsigned long *p = ((unsigned long *)addr) + BITOP_WORD(nr);
	unsigned long old;
	unsigned long flags;

	_atomic_spin_lock_irqsave(p, flags);
	old = *p;
	*p = old ^ mask;
	_atomic_spin_unlock_irqrestore(p, flags);

	return (old & mask) != 0;
}

#endif /* _ASM_GENERIC_BITOPS_ATOMIC_H */