1 | /* SPDX-License-Identifier: GPL-2.0 */ |
2 | /* rwsem.h: R/W semaphores, public interface |
3 | * |
4 | * Written by David Howells (dhowells@redhat.com). |
5 | * Derived from asm-i386/semaphore.h |
6 | */ |
7 | |
8 | #ifndef _LINUX_RWSEM_H |
9 | #define _LINUX_RWSEM_H |
10 | |
11 | #include <linux/linkage.h> |
12 | |
13 | #include <linux/types.h> |
14 | #include <linux/list.h> |
15 | #include <linux/spinlock.h> |
16 | #include <linux/atomic.h> |
17 | #include <linux/err.h> |
18 | |
19 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
20 | # define __RWSEM_DEP_MAP_INIT(lockname) \ |
21 | .dep_map = { \ |
22 | .name = #lockname, \ |
23 | .wait_type_inner = LD_WAIT_SLEEP, \ |
24 | }, |
25 | #else |
26 | # define __RWSEM_DEP_MAP_INIT(lockname) |
27 | #endif |
28 | |
29 | #ifndef CONFIG_PREEMPT_RT |
30 | |
31 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
32 | #include <linux/osq_lock.h> |
33 | #endif |
34 | |
35 | /* |
36 | * For an uncontended rwsem, count and owner are the only fields a task |
37 | * needs to touch when acquiring the rwsem. So they are put next to each |
38 | * other to increase the chance that they will share the same cacheline. |
39 | * |
40 | * In a contended rwsem, the owner is likely the most frequently accessed |
41 | * field in the structure as the optimistic waiter that holds the osq lock |
42 | * will spin on owner. For an embedded rwsem, other hot fields in the |
43 | * containing structure should be moved further away from the rwsem to |
44 | * reduce the chance that they will share the same cacheline causing |
45 | * cacheline bouncing problem. |
46 | */ |
47 | struct rw_semaphore { |
48 | atomic_long_t count; |
49 | /* |
50 | * Write owner or one of the read owners as well flags regarding |
51 | * the current state of the rwsem. Can be used as a speculative |
52 | * check to see if the write owner is running on the cpu. |
53 | */ |
54 | atomic_long_t owner; |
55 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
56 | struct optimistic_spin_queue osq; /* spinner MCS lock */ |
57 | #endif |
58 | raw_spinlock_t wait_lock; |
59 | struct list_head wait_list; |
60 | #ifdef CONFIG_DEBUG_RWSEMS |
61 | void *magic; |
62 | #endif |
63 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
64 | struct lockdep_map dep_map; |
65 | #endif |
66 | }; |
67 | |
68 | /* In all implementations count != 0 means locked */ |
69 | static inline int rwsem_is_locked(struct rw_semaphore *sem) |
70 | { |
71 | return atomic_long_read(&sem->count) != 0; |
72 | } |
73 | |
74 | #define RWSEM_UNLOCKED_VALUE 0L |
75 | #define __RWSEM_COUNT_INIT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE) |
76 | |
77 | /* Common initializer macros and functions */ |
78 | |
79 | #ifdef CONFIG_DEBUG_RWSEMS |
80 | # define __RWSEM_DEBUG_INIT(lockname) .magic = &lockname, |
81 | #else |
82 | # define __RWSEM_DEBUG_INIT(lockname) |
83 | #endif |
84 | |
85 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
86 | #define __RWSEM_OPT_INIT(lockname) .osq = OSQ_LOCK_UNLOCKED, |
87 | #else |
88 | #define __RWSEM_OPT_INIT(lockname) |
89 | #endif |
90 | |
91 | #define __RWSEM_INITIALIZER(name) \ |
92 | { __RWSEM_COUNT_INIT(name), \ |
93 | .owner = ATOMIC_LONG_INIT(0), \ |
94 | __RWSEM_OPT_INIT(name) \ |
95 | .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),\ |
96 | .wait_list = LIST_HEAD_INIT((name).wait_list), \ |
97 | __RWSEM_DEBUG_INIT(name) \ |
98 | __RWSEM_DEP_MAP_INIT(name) } |
99 | |
100 | #define DECLARE_RWSEM(name) \ |
101 | struct rw_semaphore name = __RWSEM_INITIALIZER(name) |
102 | |
103 | extern void __init_rwsem(struct rw_semaphore *sem, const char *name, |
104 | struct lock_class_key *key); |
105 | |
106 | #define init_rwsem(sem) \ |
107 | do { \ |
108 | static struct lock_class_key __key; \ |
109 | \ |
110 | __init_rwsem((sem), #sem, &__key); \ |
111 | } while (0) |
112 | |
113 | /* |
114 | * This is the same regardless of which rwsem implementation that is being used. |
115 | * It is just a heuristic meant to be called by somebody already holding the |
116 | * rwsem to see if somebody from an incompatible type is wanting access to the |
117 | * lock. |
118 | */ |
119 | static inline int rwsem_is_contended(struct rw_semaphore *sem) |
120 | { |
121 | return !list_empty(&sem->wait_list); |
122 | } |
123 | |
124 | #else /* !CONFIG_PREEMPT_RT */ |
125 | |
126 | #include <linux/rwbase_rt.h> |
127 | |
128 | struct rw_semaphore { |
129 | struct rwbase_rt rwbase; |
130 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
131 | struct lockdep_map dep_map; |
132 | #endif |
133 | }; |
134 | |
135 | #define __RWSEM_INITIALIZER(name) \ |
136 | { \ |
137 | .rwbase = __RWBASE_INITIALIZER(name), \ |
138 | __RWSEM_DEP_MAP_INIT(name) \ |
139 | } |
140 | |
141 | #define DECLARE_RWSEM(lockname) \ |
142 | struct rw_semaphore lockname = __RWSEM_INITIALIZER(lockname) |
143 | |
144 | extern void __init_rwsem(struct rw_semaphore *rwsem, const char *name, |
145 | struct lock_class_key *key); |
146 | |
147 | #define init_rwsem(sem) \ |
148 | do { \ |
149 | static struct lock_class_key __key; \ |
150 | \ |
151 | __init_rwsem((sem), #sem, &__key); \ |
152 | } while (0) |
153 | |
154 | static __always_inline int rwsem_is_locked(struct rw_semaphore *sem) |
155 | { |
156 | return rw_base_is_locked(&sem->rwbase); |
157 | } |
158 | |
159 | static __always_inline int rwsem_is_contended(struct rw_semaphore *sem) |
160 | { |
161 | return rw_base_is_contended(&sem->rwbase); |
162 | } |
163 | |
164 | #endif /* CONFIG_PREEMPT_RT */ |
165 | |
166 | /* |
167 | * The functions below are the same for all rwsem implementations including |
168 | * the RT specific variant. |
169 | */ |
170 | |
171 | /* |
172 | * lock for reading |
173 | */ |
174 | extern void down_read(struct rw_semaphore *sem); |
175 | extern int __must_check down_read_interruptible(struct rw_semaphore *sem); |
176 | extern int __must_check down_read_killable(struct rw_semaphore *sem); |
177 | |
178 | /* |
179 | * trylock for reading -- returns 1 if successful, 0 if contention |
180 | */ |
181 | extern int down_read_trylock(struct rw_semaphore *sem); |
182 | |
183 | /* |
184 | * lock for writing |
185 | */ |
186 | extern void down_write(struct rw_semaphore *sem); |
187 | extern int __must_check down_write_killable(struct rw_semaphore *sem); |
188 | |
189 | /* |
190 | * trylock for writing -- returns 1 if successful, 0 if contention |
191 | */ |
192 | extern int down_write_trylock(struct rw_semaphore *sem); |
193 | |
194 | /* |
195 | * release a read lock |
196 | */ |
197 | extern void up_read(struct rw_semaphore *sem); |
198 | |
199 | /* |
200 | * release a write lock |
201 | */ |
202 | extern void up_write(struct rw_semaphore *sem); |
203 | |
204 | /* |
205 | * downgrade write lock to read lock |
206 | */ |
207 | extern void downgrade_write(struct rw_semaphore *sem); |
208 | |
209 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
210 | /* |
211 | * nested locking. NOTE: rwsems are not allowed to recurse |
212 | * (which occurs if the same task tries to acquire the same |
213 | * lock instance multiple times), but multiple locks of the |
214 | * same lock class might be taken, if the order of the locks |
215 | * is always the same. This ordering rule can be expressed |
216 | * to lockdep via the _nested() APIs, but enumerating the |
217 | * subclasses that are used. (If the nesting relationship is |
218 | * static then another method for expressing nested locking is |
219 | * the explicit definition of lock class keys and the use of |
220 | * lockdep_set_class() at lock initialization time. |
221 | * See Documentation/locking/lockdep-design.rst for more details.) |
222 | */ |
223 | extern void down_read_nested(struct rw_semaphore *sem, int subclass); |
224 | extern int __must_check down_read_killable_nested(struct rw_semaphore *sem, int subclass); |
225 | extern void down_write_nested(struct rw_semaphore *sem, int subclass); |
226 | extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass); |
227 | extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock); |
228 | |
229 | # define down_write_nest_lock(sem, nest_lock) \ |
230 | do { \ |
231 | typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \ |
232 | _down_write_nest_lock(sem, &(nest_lock)->dep_map); \ |
233 | } while (0) |
234 | |
235 | /* |
236 | * Take/release a lock when not the owner will release it. |
237 | * |
238 | * [ This API should be avoided as much as possible - the |
239 | * proper abstraction for this case is completions. ] |
240 | */ |
241 | extern void down_read_non_owner(struct rw_semaphore *sem); |
242 | extern void up_read_non_owner(struct rw_semaphore *sem); |
243 | #else |
244 | # define down_read_nested(sem, subclass) down_read(sem) |
245 | # define down_read_killable_nested(sem, subclass) down_read_killable(sem) |
246 | # define down_write_nest_lock(sem, nest_lock) down_write(sem) |
247 | # define down_write_nested(sem, subclass) down_write(sem) |
248 | # define down_write_killable_nested(sem, subclass) down_write_killable(sem) |
249 | # define down_read_non_owner(sem) down_read(sem) |
250 | # define up_read_non_owner(sem) up_read(sem) |
251 | #endif |
252 | |
253 | #endif /* _LINUX_RWSEM_H */ |
254 | |