1 /* SPDX-License-Identifier: GPL-2.0 */
7 * Shared/intent/exclusive locks: sleepable read/write locks, much like rw
8 * semaphores, except with a third intermediate state, intent. Basic operations
11 * six_lock_read(&foo->lock);
12 * six_unlock_read(&foo->lock);
14 * six_lock_intent(&foo->lock);
15 * six_unlock_intent(&foo->lock);
17 * six_lock_write(&foo->lock);
18 * six_unlock_write(&foo->lock);
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:
23 * six_lock_intent(&foo->lock);
24 * six_lock_write(&foo->lock);
25 * six_unlock_write(&foo->lock);
26 * six_unlock_intent(&foo->lock);
31 * six_trylock_intent()
34 * six_lock_downgrade(): convert from intent to read
35 * six_lock_tryupgrade(): attempt to convert from read to intent
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.
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:
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)
52 * A lock may be held multiple types 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.
61 #include <linux/lockdep.h>
62 #include <linux/osq_lock.h>
63 #include <linux/sched.h>
64 #include <linux/types.h>
66 #define SIX_LOCK_SEPARATE_LOCKFNS
68 union six_lock_state {
78 /* for waitlist_bitnr() */
83 unsigned read_lock:26;
84 unsigned write_locking:1;
85 unsigned intent_lock:1;
89 * seq works much like in seqlocks: it's incremented every time
90 * we lock and unlock for write.
92 * If it's odd write lock is held, even unlocked.
94 * Thus readers can unlock, and then lock again later iff it
95 * hasn't been modified in the meantime.
108 union six_lock_state state;
109 unsigned intent_lock_recurse;
110 struct task_struct *owner;
111 unsigned __percpu *readers;
112 struct optimistic_spin_queue osq;
113 raw_spinlock_t wait_lock;
114 struct list_head wait_list;
115 #ifdef CONFIG_DEBUG_LOCK_ALLOC
116 struct lockdep_map dep_map;
120 struct six_lock_waiter {
121 struct list_head list;
122 struct task_struct *task;
123 enum six_lock_type lock_want;
128 typedef int (*six_lock_should_sleep_fn)(struct six_lock *lock, void *);
130 static __always_inline void __six_lock_init(struct six_lock *lock,
132 struct lock_class_key *key)
134 atomic64_set(&lock->state.counter, 0);
135 raw_spin_lock_init(&lock->wait_lock);
136 INIT_LIST_HEAD(&lock->wait_list);
137 #ifdef CONFIG_DEBUG_LOCK_ALLOC
138 debug_check_no_locks_freed((void *) lock, sizeof(*lock));
139 lockdep_init_map(&lock->dep_map, name, key, 0);
143 #define six_lock_init(lock) \
145 static struct lock_class_key __key; \
147 __six_lock_init((lock), #lock, &__key); \
150 #define __SIX_VAL(field, _v) (((union six_lock_state) { .field = _v }).v)
152 #define __SIX_LOCK(type) \
153 bool six_trylock_ip_##type(struct six_lock *, unsigned long); \
154 bool six_relock_ip_##type(struct six_lock *, u32, unsigned long); \
155 int six_lock_ip_##type(struct six_lock *, six_lock_should_sleep_fn, \
156 void *, unsigned long); \
157 int six_lock_ip_waiter_##type(struct six_lock *, struct six_lock_waiter *,\
158 six_lock_should_sleep_fn, void *, unsigned long);\
159 void six_unlock_ip_##type(struct six_lock *, unsigned long); \
161 static inline bool six_trylock_##type(struct six_lock *lock) \
163 return six_trylock_ip_##type(lock, _THIS_IP_); \
165 static inline bool six_relock_##type(struct six_lock *lock, u32 seq) \
167 return six_relock_ip_##type(lock, seq, _THIS_IP_); \
169 static inline int six_lock_##type(struct six_lock *lock, \
170 six_lock_should_sleep_fn fn, void *p)\
172 return six_lock_ip_##type(lock, fn, p, _THIS_IP_); \
174 static inline int six_lock_waiter_##type(struct six_lock *lock, \
175 struct six_lock_waiter *wait, \
176 six_lock_should_sleep_fn fn, void *p) \
178 return six_lock_ip_waiter_##type(lock, wait, fn, p, _THIS_IP_); \
180 static inline void six_unlock_##type(struct six_lock *lock) \
182 return six_unlock_ip_##type(lock, _THIS_IP_); \
190 #define SIX_LOCK_DISPATCH(type, fn, ...) \
192 case SIX_LOCK_read: \
193 return fn##_read(__VA_ARGS__); \
194 case SIX_LOCK_intent: \
195 return fn##_intent(__VA_ARGS__); \
196 case SIX_LOCK_write: \
197 return fn##_write(__VA_ARGS__); \
202 static inline bool six_trylock_type(struct six_lock *lock, enum six_lock_type type)
204 SIX_LOCK_DISPATCH(type, six_trylock, lock);
207 static inline bool six_relock_type(struct six_lock *lock, enum six_lock_type type,
210 SIX_LOCK_DISPATCH(type, six_relock, lock, seq);
213 static inline int six_lock_type(struct six_lock *lock, enum six_lock_type type,
214 six_lock_should_sleep_fn should_sleep_fn, void *p)
216 SIX_LOCK_DISPATCH(type, six_lock, lock, should_sleep_fn, p);
219 static inline int six_lock_type_ip_waiter(struct six_lock *lock, enum six_lock_type type,
220 struct six_lock_waiter *wait,
221 six_lock_should_sleep_fn should_sleep_fn, void *p,
224 SIX_LOCK_DISPATCH(type, six_lock_ip_waiter, lock, wait, should_sleep_fn, p, ip);
227 static inline int six_lock_type_waiter(struct six_lock *lock, enum six_lock_type type,
228 struct six_lock_waiter *wait,
229 six_lock_should_sleep_fn should_sleep_fn, void *p)
231 SIX_LOCK_DISPATCH(type, six_lock_waiter, lock, wait, should_sleep_fn, p);
234 static inline void six_unlock_type(struct six_lock *lock, enum six_lock_type type)
236 SIX_LOCK_DISPATCH(type, six_unlock, lock);
239 void six_lock_downgrade(struct six_lock *);
240 bool six_lock_tryupgrade(struct six_lock *);
241 bool six_trylock_convert(struct six_lock *, enum six_lock_type,
244 void six_lock_increment(struct six_lock *, enum six_lock_type);
246 void six_lock_wakeup_all(struct six_lock *);
248 void six_lock_pcpu_free(struct six_lock *);
249 void six_lock_pcpu_alloc(struct six_lock *);
251 struct six_lock_count {
255 struct six_lock_count six_lock_counts(struct six_lock *);
257 #endif /* _LINUX_SIX_H */