bit_spinlock.h

  1/* SPDX-License-Identifier: GPL-2.0 */
  2#ifndef __LINUX_BIT_SPINLOCK_H
  3#define __LINUX_BIT_SPINLOCK_H
  4
  5#include <linux/kernel.h>
  6#include <linux/preempt.h>
  7#include <linux/atomic.h>
  8#include <linux/bug.h>
  9
 10/*
 11 *  bit-based spin_lock()
 12 *
 13 * Don't use this unless you really need to: spin_lock() and spin_unlock()
 14 * are significantly faster.
 15 */
 16static __always_inline void bit_spin_lock(int bitnum, unsigned long *addr)
 17{
 18	/*
 19	 * Assuming the lock is uncontended, this never enters
 20	 * the body of the outer loop. If it is contended, then
 21	 * within the inner loop a non-atomic test is used to
 22	 * busywait with less bus contention for a good time to
 23	 * attempt to acquire the lock bit.
 24	 */
 25	preempt_disable();
 26#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
 27	while (unlikely(test_and_set_bit_lock(bitnum, addr))) {
 28		preempt_enable();
 29		do {
 30			cpu_relax();
 31		} while (test_bit(bitnum, addr));
 32		preempt_disable();
 33	}
 34#endif
 35	__acquire(bitlock);
 36}
 37
 38/*
 39 * Return true if it was acquired
 40 */
 41static __always_inline int bit_spin_trylock(int bitnum, unsigned long *addr)
 42{
 43	preempt_disable();
 44#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
 45	if (unlikely(test_and_set_bit_lock(bitnum, addr))) {
 46		preempt_enable();
 47		return 0;
 48	}
 49#endif
 50	__acquire(bitlock);
 51	return 1;
 52}
 53
 54/*
 55 *  bit-based spin_unlock()
 56 */
 57static __always_inline void bit_spin_unlock(int bitnum, unsigned long *addr)
 58{
 59#ifdef CONFIG_DEBUG_SPINLOCK
 60	BUG_ON(!test_bit(bitnum, addr));
 61#endif
 62#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
 63	clear_bit_unlock(bitnum, addr);
 64#endif
 65	preempt_enable();
 66	__release(bitlock);
 67}
 68
 69/*
 70 *  bit-based spin_unlock()
 71 *  non-atomic version, which can be used eg. if the bit lock itself is
 72 *  protecting the rest of the flags in the word.
 73 */
 74static __always_inline void __bit_spin_unlock(int bitnum, unsigned long *addr)
 75{
 76#ifdef CONFIG_DEBUG_SPINLOCK
 77	BUG_ON(!test_bit(bitnum, addr));
 78#endif
 79#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
 80	__clear_bit_unlock(bitnum, addr);
 81#endif
 82	preempt_enable();
 83	__release(bitlock);
 84}
 85
 86/*
 87 * Return true if the lock is held.
 88 */
 89static inline int bit_spin_is_locked(int bitnum, unsigned long *addr)
 90{
 91#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
 92	return test_bit(bitnum, addr);
 93#elif defined CONFIG_PREEMPT_COUNT
 94	return preempt_count();
 95#else
 96	return 1;
 97#endif
 98}
 99
100#endif /* __LINUX_BIT_SPINLOCK_H */
101