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locking/atomics, asm-generic/bitops/atomic.h: Rewrite using atomic_*(…
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…) APIs

The atomic bitops can actually be implemented pretty efficiently using
the atomic_*() ops, rather than explicit use of spinlocks.

Signed-off-by: Will Deacon <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: https://lore.kernel.org/lkml/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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wildea01 authored and Ingo Molnar committed Jun 21, 2018
1 parent 1c2672b commit e986a0d
Showing 1 changed file with 33 additions and 155 deletions.
188 changes: 33 additions & 155 deletions include/asm-generic/bitops/atomic.h
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#ifndef _ASM_GENERIC_BITOPS_ATOMIC_H_
#define _ASM_GENERIC_BITOPS_ATOMIC_H_

#include <asm/types.h>
#include <linux/irqflags.h>

#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 arch_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 { \
arch_spinlock_t *s = ATOMIC_HASH(l); \
local_irq_save(f); \
arch_spin_lock(s); \
} while(0)

#define _atomic_spin_unlock_irqrestore(l,f) do { \
arch_spinlock_t *s = ATOMIC_HASH(l); \
arch_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
#include <linux/atomic.h>
#include <linux/compiler.h>
#include <asm/barrier.h>

/*
* 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
* Implementation of atomic bitops using atomic-fetch ops.
* See Documentation/atomic_bitops.txt for details.
*/

/**
* 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)
static inline void set_bit(unsigned int nr, volatile unsigned long *p)
{
unsigned long mask = BIT_MASK(nr);
unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
unsigned long flags;

_atomic_spin_lock_irqsave(p, flags);
*p |= mask;
_atomic_spin_unlock_irqrestore(p, flags);
p += BIT_WORD(nr);
atomic_long_or(BIT_MASK(nr), (atomic_long_t *)p);
}

/**
* 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_atomic() and/or smp_mb__after_atomic()
* in order to ensure changes are visible on other processors.
*/
static inline void clear_bit(int nr, volatile unsigned long *addr)
static inline void clear_bit(unsigned int nr, volatile unsigned long *p)
{
unsigned long mask = BIT_MASK(nr);
unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
unsigned long flags;

_atomic_spin_lock_irqsave(p, flags);
*p &= ~mask;
_atomic_spin_unlock_irqrestore(p, flags);
p += BIT_WORD(nr);
atomic_long_andnot(BIT_MASK(nr), (atomic_long_t *)p);
}

/**
* 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)
static inline void change_bit(unsigned int nr, volatile unsigned long *p)
{
unsigned long mask = BIT_MASK(nr);
unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
unsigned long flags;

_atomic_spin_lock_irqsave(p, flags);
*p ^= mask;
_atomic_spin_unlock_irqrestore(p, flags);
p += BIT_WORD(nr);
atomic_long_xor(BIT_MASK(nr), (atomic_long_t *)p);
}

/**
* 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)
static inline int test_and_set_bit(unsigned int nr, volatile unsigned long *p)
{
long old;
unsigned long mask = BIT_MASK(nr);
unsigned long *p = ((unsigned long *)addr) + BIT_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);
p += BIT_WORD(nr);
if (READ_ONCE(*p) & mask)
return 1;

return (old & mask) != 0;
old = atomic_long_fetch_or(mask, (atomic_long_t *)p);
return !!(old & mask);
}

/**
* 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)
static inline int test_and_clear_bit(unsigned int nr, volatile unsigned long *p)
{
long old;
unsigned long mask = BIT_MASK(nr);
unsigned long *p = ((unsigned long *)addr) + BIT_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);
p += BIT_WORD(nr);
if (!(READ_ONCE(*p) & mask))
return 0;

return (old & mask) != 0;
old = atomic_long_fetch_andnot(mask, (atomic_long_t *)p);
return !!(old & mask);
}

/**
* 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)
static inline int test_and_change_bit(unsigned int nr, volatile unsigned long *p)
{
long old;
unsigned long mask = BIT_MASK(nr);
unsigned long *p = ((unsigned long *)addr) + BIT_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;
p += BIT_WORD(nr);
old = atomic_long_fetch_xor(mask, (atomic_long_t *)p);
return !!(old & mask);
}

#endif /* _ASM_GENERIC_BITOPS_ATOMIC_H */

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