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84c6591103
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>
92 lines
2.4 KiB
C
92 lines
2.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_GENERIC_BITOPS_LOCK_H_
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#define _ASM_GENERIC_BITOPS_LOCK_H_
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#include <linux/atomic.h>
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#include <linux/compiler.h>
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#include <asm/barrier.h>
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/**
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* test_and_set_bit_lock - Set a bit and return its old value, for lock
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* @nr: Bit to set
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* @addr: Address to count from
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*
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* This operation is atomic and provides acquire barrier semantics if
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* the returned value is 0.
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* It can be used to implement bit locks.
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*/
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static inline int test_and_set_bit_lock(unsigned int nr,
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volatile unsigned long *p)
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{
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long old;
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unsigned long mask = BIT_MASK(nr);
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p += BIT_WORD(nr);
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if (READ_ONCE(*p) & mask)
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return 1;
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old = atomic_long_fetch_or_acquire(mask, (atomic_long_t *)p);
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return !!(old & mask);
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}
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/**
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* clear_bit_unlock - Clear a bit in memory, for unlock
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* @nr: the bit to set
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* @addr: the address to start counting from
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*
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* This operation is atomic and provides release barrier semantics.
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*/
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static inline void clear_bit_unlock(unsigned int nr, volatile unsigned long *p)
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{
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p += BIT_WORD(nr);
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atomic_long_fetch_andnot_release(BIT_MASK(nr), (atomic_long_t *)p);
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}
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/**
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* __clear_bit_unlock - Clear a bit in memory, for unlock
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* @nr: the bit to set
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* @addr: the address to start counting from
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*
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* A weaker form of clear_bit_unlock() as used by __bit_lock_unlock(). If all
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* the bits in the word are protected by this lock some archs can use weaker
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* ops to safely unlock.
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*
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* See for example x86's implementation.
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*/
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static inline void __clear_bit_unlock(unsigned int nr,
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volatile unsigned long *p)
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{
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unsigned long old;
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p += BIT_WORD(nr);
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old = READ_ONCE(*p);
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old &= ~BIT_MASK(nr);
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atomic_long_set_release((atomic_long_t *)p, old);
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}
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/**
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* clear_bit_unlock_is_negative_byte - Clear a bit in memory and test if bottom
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* byte is negative, for unlock.
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* @nr: the bit to clear
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* @addr: the address to start counting from
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*
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* This is a bit of a one-trick-pony for the filemap code, which clears
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* PG_locked and tests PG_waiters,
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*/
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#ifndef clear_bit_unlock_is_negative_byte
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static inline bool clear_bit_unlock_is_negative_byte(unsigned int nr,
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volatile unsigned long *p)
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{
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long old;
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unsigned long mask = BIT_MASK(nr);
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p += BIT_WORD(nr);
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old = atomic_long_fetch_andnot_release(mask, (atomic_long_t *)p);
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return !!(old & BIT(7));
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}
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#define clear_bit_unlock_is_negative_byte clear_bit_unlock_is_negative_byte
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#endif
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#endif /* _ASM_GENERIC_BITOPS_LOCK_H_ */
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