1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_PERCPU_RWSEM_H
3 #define _LINUX_PERCPU_RWSEM_H
4
5 #include <linux/atomic.h>
6 #include <linux/percpu.h>
7 #include <linux/rcuwait.h>
8 #include <linux/wait.h>
9 #include <linux/rcu_sync.h>
10 #include <linux/lockdep.h>
11
12 struct percpu_rw_semaphore {
13 struct rcu_sync rss;
14 unsigned int __percpu *read_count;
15 struct rcuwait writer;
16 wait_queue_head_t waiters;
17 atomic_t block;
18 #ifdef CONFIG_DEBUG_LOCK_ALLOC
19 struct lockdep_map dep_map;
20 #endif
21 ANDROID_OEM_DATA(1);
22 };
23
24 void _trace_android_vh_record_pcpu_rwsem_starttime(
25 struct percpu_rw_semaphore *sem, unsigned long settime);
26
27 #ifdef CONFIG_DEBUG_LOCK_ALLOC
28 #define __PERCPU_RWSEM_DEP_MAP_INIT(lockname) .dep_map = { .name = #lockname },
29 #else
30 #define __PERCPU_RWSEM_DEP_MAP_INIT(lockname)
31 #endif
32
33 #define __DEFINE_PERCPU_RWSEM(name, is_static) \
34 static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name); \
35 is_static struct percpu_rw_semaphore name = { \
36 .rss = __RCU_SYNC_INITIALIZER(name.rss), \
37 .read_count = &__percpu_rwsem_rc_##name, \
38 .writer = __RCUWAIT_INITIALIZER(name.writer), \
39 .waiters = __WAIT_QUEUE_HEAD_INITIALIZER(name.waiters), \
40 .block = ATOMIC_INIT(0), \
41 __PERCPU_RWSEM_DEP_MAP_INIT(name) \
42 }
43
44 #define DEFINE_PERCPU_RWSEM(name) \
45 __DEFINE_PERCPU_RWSEM(name, /* not static */)
46 #define DEFINE_STATIC_PERCPU_RWSEM(name) \
47 __DEFINE_PERCPU_RWSEM(name, static)
48
49 extern bool __percpu_down_read(struct percpu_rw_semaphore *, bool);
50
percpu_down_read(struct percpu_rw_semaphore * sem)51 static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
52 {
53 might_sleep();
54
55 rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
56
57 preempt_disable();
58 /*
59 * We are in an RCU-sched read-side critical section, so the writer
60 * cannot both change sem->state from readers_fast and start checking
61 * counters while we are here. So if we see !sem->state, we know that
62 * the writer won't be checking until we're past the preempt_enable()
63 * and that once the synchronize_rcu() is done, the writer will see
64 * anything we did within this RCU-sched read-size critical section.
65 */
66 if (likely(rcu_sync_is_idle(&sem->rss)))
67 this_cpu_inc(*sem->read_count);
68 else
69 __percpu_down_read(sem, false); /* Unconditional memory barrier */
70 /*
71 * The preempt_enable() prevents the compiler from
72 * bleeding the critical section out.
73 */
74 _trace_android_vh_record_pcpu_rwsem_starttime(sem, jiffies);
75 preempt_enable();
76 }
77
percpu_down_read_trylock(struct percpu_rw_semaphore * sem)78 static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
79 {
80 bool ret = true;
81
82 preempt_disable();
83 /*
84 * Same as in percpu_down_read().
85 */
86 if (likely(rcu_sync_is_idle(&sem->rss)))
87 this_cpu_inc(*sem->read_count);
88 else
89 ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
90 preempt_enable();
91 /*
92 * The barrier() from preempt_enable() prevents the compiler from
93 * bleeding the critical section out.
94 */
95
96 if (ret) {
97 _trace_android_vh_record_pcpu_rwsem_starttime(sem, jiffies);
98 rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
99 }
100
101 return ret;
102 }
103
percpu_up_read(struct percpu_rw_semaphore * sem)104 static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
105 {
106 rwsem_release(&sem->dep_map, _RET_IP_);
107
108 preempt_disable();
109 /*
110 * Same as in percpu_down_read().
111 */
112 if (likely(rcu_sync_is_idle(&sem->rss))) {
113 this_cpu_dec(*sem->read_count);
114 } else {
115 /*
116 * slowpath; reader will only ever wake a single blocked
117 * writer.
118 */
119 smp_mb(); /* B matches C */
120 /*
121 * In other words, if they see our decrement (presumably to
122 * aggregate zero, as that is the only time it matters) they
123 * will also see our critical section.
124 */
125 this_cpu_dec(*sem->read_count);
126 rcuwait_wake_up(&sem->writer);
127 }
128 _trace_android_vh_record_pcpu_rwsem_starttime(sem, 0);
129 preempt_enable();
130 }
131
132 extern bool percpu_is_read_locked(struct percpu_rw_semaphore *);
133 extern void percpu_down_write(struct percpu_rw_semaphore *);
134 extern void percpu_up_write(struct percpu_rw_semaphore *);
135
percpu_is_write_locked(struct percpu_rw_semaphore * sem)136 static inline bool percpu_is_write_locked(struct percpu_rw_semaphore *sem)
137 {
138 return atomic_read(&sem->block);
139 }
140
141 extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
142 const char *, struct lock_class_key *);
143
144 extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
145
146 #define percpu_init_rwsem(sem) \
147 ({ \
148 static struct lock_class_key rwsem_key; \
149 __percpu_init_rwsem(sem, #sem, &rwsem_key); \
150 })
151
152 #define percpu_rwsem_is_held(sem) lockdep_is_held(sem)
153 #define percpu_rwsem_assert_held(sem) lockdep_assert_held(sem)
154
percpu_rwsem_release(struct percpu_rw_semaphore * sem,unsigned long ip)155 static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
156 unsigned long ip)
157 {
158 lock_release(&sem->dep_map, ip);
159 }
160
percpu_rwsem_acquire(struct percpu_rw_semaphore * sem,bool read,unsigned long ip)161 static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
162 bool read, unsigned long ip)
163 {
164 lock_acquire(&sem->dep_map, 0, 1, read, 1, NULL, ip);
165 }
166
167 #endif
168