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61e02392d3
A test_and_{}_bit() operation fails if the value of the bit is such that
the modification does not take place. For example, if test_and_set_bit()
returns 1. In these cases, follow the behaviour of cmpxchg and allow the
operation to be unordered. This also applies to test_and_set_bit_lock()
if the lock is found to be be taken already.
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: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1518528619-20049-1-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
47 lines
1.3 KiB
C
47 lines
1.3 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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/**
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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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#define test_and_set_bit_lock(nr, addr) test_and_set_bit(nr, addr)
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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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#define clear_bit_unlock(nr, addr) \
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do { \
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smp_mb__before_atomic(); \
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clear_bit(nr, addr); \
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} while (0)
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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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#define __clear_bit_unlock(nr, addr) \
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do { \
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smp_mb__before_atomic(); \
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clear_bit(nr, addr); \
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} while (0)
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#endif /* _ASM_GENERIC_BITOPS_LOCK_H_ */
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