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 */
16 static 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 */
41 static 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 */
57 static 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 */
74 static 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 */
89 static 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
102
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