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1 | /* SPDX-License-Identifier: GPL-2.0 */ |
2 | ||
3 | #ifndef _LINUX_SIX_H | |
4 | #define _LINUX_SIX_H | |
5 | ||
6 | /* | |
7 | * Shared/intent/exclusive locks: sleepable read/write locks, much like rw | |
8 | * semaphores, except with a third intermediate state, intent. Basic operations | |
9 | * are: | |
10 | * | |
11 | * six_lock_read(&foo->lock); | |
12 | * six_unlock_read(&foo->lock); | |
13 | * | |
14 | * six_lock_intent(&foo->lock); | |
15 | * six_unlock_intent(&foo->lock); | |
16 | * | |
17 | * six_lock_write(&foo->lock); | |
18 | * six_unlock_write(&foo->lock); | |
19 | * | |
20 | * Intent locks block other intent locks, but do not block read locks, and you | |
21 | * must have an intent lock held before taking a write lock, like so: | |
22 | * | |
23 | * six_lock_intent(&foo->lock); | |
24 | * six_lock_write(&foo->lock); | |
25 | * six_unlock_write(&foo->lock); | |
26 | * six_unlock_intent(&foo->lock); | |
27 | * | |
28 | * Other operations: | |
29 | * | |
30 | * six_trylock_read() | |
31 | * six_trylock_intent() | |
32 | * six_trylock_write() | |
33 | * | |
34 | * six_lock_downgrade(): convert from intent to read | |
35 | * six_lock_tryupgrade(): attempt to convert from read to intent | |
36 | * | |
37 | * Locks also embed a sequence number, which is incremented when the lock is | |
38 | * locked or unlocked for write. The current sequence number can be grabbed | |
39 | * while a lock is held from lock->state.seq; then, if you drop the lock you can | |
40 | * use six_relock_(read|intent_write)(lock, seq) to attempt to retake the lock | |
41 | * iff it hasn't been locked for write in the meantime. | |
42 | * | |
43 | * There are also operations that take the lock type as a parameter, where the | |
44 | * type is one of SIX_LOCK_read, SIX_LOCK_intent, or SIX_LOCK_write: | |
45 | * | |
46 | * six_lock_type(lock, type) | |
47 | * six_unlock_type(lock, type) | |
48 | * six_relock(lock, type, seq) | |
49 | * six_trylock_type(lock, type) | |
50 | * six_trylock_convert(lock, from, to) | |
51 | * | |
52 | * A lock may be held multiple times by the same thread (for read or intent, | |
53 | * not write). However, the six locks code does _not_ implement the actual | |
54 | * recursive checks itself though - rather, if your code (e.g. btree iterator | |
55 | * code) knows that the current thread already has a lock held, and for the | |
56 | * correct type, six_lock_increment() may be used to bump up the counter for | |
57 | * that type - the only effect is that one more call to unlock will be required | |
58 | * before the lock is unlocked. | |
59 | */ | |
60 | ||
61 | #include <linux/lockdep.h> | |
62 | #include <linux/sched.h> | |
63 | #include <linux/types.h> | |
64 | ||
65 | #ifdef CONFIG_SIX_LOCK_SPIN_ON_OWNER | |
66 | #include <linux/osq_lock.h> | |
67 | #endif | |
68 | ||
69 | #define SIX_LOCK_SEPARATE_LOCKFNS | |
70 | ||
71 | union six_lock_state { | |
72 | struct { | |
73 | atomic64_t counter; | |
74 | }; | |
75 | ||
76 | struct { | |
77 | u64 v; | |
78 | }; | |
79 | ||
80 | struct { | |
81 | /* for waitlist_bitnr() */ | |
82 | unsigned long l; | |
83 | }; | |
84 | ||
85 | struct { | |
86 | unsigned read_lock:27; | |
87 | unsigned write_locking:1; | |
88 | unsigned intent_lock:1; | |
89 | unsigned waiters:3; | |
90 | /* | |
91 | * seq works much like in seqlocks: it's incremented every time | |
92 | * we lock and unlock for write. | |
93 | * | |
94 | * If it's odd write lock is held, even unlocked. | |
95 | * | |
96 | * Thus readers can unlock, and then lock again later iff it | |
97 | * hasn't been modified in the meantime. | |
98 | */ | |
99 | u32 seq; | |
100 | }; | |
101 | }; | |
102 | ||
103 | enum six_lock_type { | |
104 | SIX_LOCK_read, | |
105 | SIX_LOCK_intent, | |
106 | SIX_LOCK_write, | |
107 | }; | |
108 | ||
109 | struct six_lock { | |
110 | union six_lock_state state; | |
111 | unsigned intent_lock_recurse; | |
112 | struct task_struct *owner; | |
113 | #ifdef CONFIG_SIX_LOCK_SPIN_ON_OWNER | |
114 | struct optimistic_spin_queue osq; | |
115 | #endif | |
116 | unsigned __percpu *readers; | |
117 | ||
118 | raw_spinlock_t wait_lock; | |
119 | struct list_head wait_list[2]; | |
120 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
121 | struct lockdep_map dep_map; | |
122 | #endif | |
123 | }; | |
124 | ||
125 | typedef int (*six_lock_should_sleep_fn)(struct six_lock *lock, void *); | |
126 | ||
127 | static __always_inline void __six_lock_init(struct six_lock *lock, | |
128 | const char *name, | |
129 | struct lock_class_key *key) | |
130 | { | |
131 | atomic64_set(&lock->state.counter, 0); | |
132 | raw_spin_lock_init(&lock->wait_lock); | |
133 | INIT_LIST_HEAD(&lock->wait_list[SIX_LOCK_read]); | |
134 | INIT_LIST_HEAD(&lock->wait_list[SIX_LOCK_intent]); | |
135 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
136 | debug_check_no_locks_freed((void *) lock, sizeof(*lock)); | |
137 | lockdep_init_map(&lock->dep_map, name, key, 0); | |
138 | #endif | |
139 | } | |
140 | ||
141 | #define six_lock_init(lock) \ | |
142 | do { \ | |
143 | static struct lock_class_key __key; \ | |
144 | \ | |
145 | __six_lock_init((lock), #lock, &__key); \ | |
146 | } while (0) | |
147 | ||
148 | #define __SIX_VAL(field, _v) (((union six_lock_state) { .field = _v }).v) | |
149 | ||
150 | #define __SIX_LOCK(type) \ | |
151 | bool six_trylock_##type(struct six_lock *); \ | |
152 | bool six_relock_##type(struct six_lock *, u32); \ | |
153 | int six_lock_##type(struct six_lock *, six_lock_should_sleep_fn, void *);\ | |
154 | void six_unlock_##type(struct six_lock *); | |
155 | ||
156 | __SIX_LOCK(read) | |
157 | __SIX_LOCK(intent) | |
158 | __SIX_LOCK(write) | |
159 | #undef __SIX_LOCK | |
160 | ||
161 | #define SIX_LOCK_DISPATCH(type, fn, ...) \ | |
162 | switch (type) { \ | |
163 | case SIX_LOCK_read: \ | |
164 | return fn##_read(__VA_ARGS__); \ | |
165 | case SIX_LOCK_intent: \ | |
166 | return fn##_intent(__VA_ARGS__); \ | |
167 | case SIX_LOCK_write: \ | |
168 | return fn##_write(__VA_ARGS__); \ | |
169 | default: \ | |
170 | BUG(); \ | |
171 | } | |
172 | ||
173 | static inline bool six_trylock_type(struct six_lock *lock, enum six_lock_type type) | |
174 | { | |
175 | SIX_LOCK_DISPATCH(type, six_trylock, lock); | |
176 | } | |
177 | ||
178 | static inline bool six_relock_type(struct six_lock *lock, enum six_lock_type type, | |
179 | unsigned seq) | |
180 | { | |
181 | SIX_LOCK_DISPATCH(type, six_relock, lock, seq); | |
182 | } | |
183 | ||
184 | static inline int six_lock_type(struct six_lock *lock, enum six_lock_type type, | |
185 | six_lock_should_sleep_fn should_sleep_fn, void *p) | |
186 | { | |
187 | SIX_LOCK_DISPATCH(type, six_lock, lock, should_sleep_fn, p); | |
188 | } | |
189 | ||
190 | static inline void six_unlock_type(struct six_lock *lock, enum six_lock_type type) | |
191 | { | |
192 | SIX_LOCK_DISPATCH(type, six_unlock, lock); | |
193 | } | |
194 | ||
195 | void six_lock_downgrade(struct six_lock *); | |
196 | bool six_lock_tryupgrade(struct six_lock *); | |
197 | bool six_trylock_convert(struct six_lock *, enum six_lock_type, | |
198 | enum six_lock_type); | |
199 | ||
200 | void six_lock_increment(struct six_lock *, enum six_lock_type); | |
201 | ||
202 | void six_lock_wakeup_all(struct six_lock *); | |
203 | ||
204 | void six_lock_pcpu_free_rcu(struct six_lock *); | |
205 | void six_lock_pcpu_free(struct six_lock *); | |
206 | void six_lock_pcpu_alloc(struct six_lock *); | |
207 | ||
208 | struct six_lock_count { | |
209 | unsigned read; | |
210 | unsigned intent; | |
211 | }; | |
212 | ||
213 | struct six_lock_count six_lock_counts(struct six_lock *); | |
214 | ||
215 | #endif /* _LINUX_SIX_H */ |