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locking/atomics, asm-generic/bitops/lock.h: Rewrite using atomic_fetch_*() 

The lock bitops can be implemented more efficiently using the atomic_fetch_*()
ops, which provide finer-grained control over the memory ordering semantics
than the bitops.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-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: linux-arm-kernel@lists.infradead.org
Cc: yamada.masahiro@socionext.com
Link: https://lore.kernel.org/lkml/1529412794-17720-8-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Will Deacon 2018-06-19 13:53:12 +01:00 committed by Ingo Molnar
parent e986a0d6cb
commit 84c6591103
1 changed files with 56 additions and 12 deletions
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68
include/asm-generic/bitops/lock.h
View File

@ -2,6 +2,10 @@
#ifndef _ASM_GENERIC_BITOPS_LOCK_H_
#define _ASM_GENERIC_BITOPS_LOCK_H_
#include <linux/atomic.h>
#include <linux/compiler.h>
#include <asm/barrier.h>
/**
* test_and_set_bit_lock - Set a bit and return its old value, for lock
* @nr: Bit to set
@ -11,7 +15,20 @@
* the returned value is 0.
* It can be used to implement bit locks.
*/
#define test_and_set_bit_lock(nr, addr) test_and_set_bit(nr, addr)
static inline int test_and_set_bit_lock(unsigned int nr,
volatile unsigned long *p)
{
long old;
unsigned long mask = BIT_MASK(nr);
p += BIT_WORD(nr);
if (READ_ONCE(*p) & mask)
return 1;
old = atomic_long_fetch_or_acquire(mask, (atomic_long_t *)p);
return !!(old & mask);
}
/**
* clear_bit_unlock - Clear a bit in memory, for unlock
@ -20,11 +37,11 @@
*
* This operation is atomic and provides release barrier semantics.
*/
#define clear_bit_unlock(nr, addr) \
do { \
smp_mb__before_atomic(); \
clear_bit(nr, addr); \
} while (0)
static inline void clear_bit_unlock(unsigned int nr, volatile unsigned long *p)
{
p += BIT_WORD(nr);
atomic_long_fetch_andnot_release(BIT_MASK(nr), (atomic_long_t *)p);
}
/**
* __clear_bit_unlock - Clear a bit in memory, for unlock
@ -37,11 +54,38 @@ do { \
*
* See for example x86's implementation.
*/
#define __clear_bit_unlock(nr, addr) \
do { \
smp_mb__before_atomic(); \
clear_bit(nr, addr); \
} while (0)
static inline void __clear_bit_unlock(unsigned int nr,
volatile unsigned long *p)
{
unsigned long old;
p += BIT_WORD(nr);
old = READ_ONCE(*p);
old &= ~BIT_MASK(nr);
atomic_long_set_release((atomic_long_t *)p, old);
}
/**
* clear_bit_unlock_is_negative_byte - Clear a bit in memory and test if bottom
* byte is negative, for unlock.
* @nr: the bit to clear
* @addr: the address to start counting from
*
* This is a bit of a one-trick-pony for the filemap code, which clears
* PG_locked and tests PG_waiters,
*/
#ifndef clear_bit_unlock_is_negative_byte
static inline bool clear_bit_unlock_is_negative_byte(unsigned int nr,
volatile unsigned long *p)
{
long old;
unsigned long mask = BIT_MASK(nr);
p += BIT_WORD(nr);
old = atomic_long_fetch_andnot_release(mask, (atomic_long_t *)p);
return !!(old & BIT(7));
}
#define clear_bit_unlock_is_negative_byte clear_bit_unlock_is_negative_byte
#endif
#endif /* _ASM_GENERIC_BITOPS_LOCK_H_ */