1 /* SPDX-License-Identifier: GPL-2.0 */ 1 /* SPDX-License-Identifier: GPL-2.0 */
2 /* rwsem.h: R/W semaphores, public interface 2 /* rwsem.h: R/W semaphores, public interface
3 * 3 *
4 * Written by David Howells (dhowells@redhat.c 4 * Written by David Howells (dhowells@redhat.com).
5 * Derived from asm-i386/semaphore.h 5 * Derived from asm-i386/semaphore.h
6 */ 6 */
7 7
8 #ifndef _LINUX_RWSEM_H 8 #ifndef _LINUX_RWSEM_H
9 #define _LINUX_RWSEM_H 9 #define _LINUX_RWSEM_H
10 10
11 #include <linux/linkage.h> 11 #include <linux/linkage.h>
12 12
13 #include <linux/types.h> 13 #include <linux/types.h>
>> 14 #include <linux/kernel.h>
14 #include <linux/list.h> 15 #include <linux/list.h>
15 #include <linux/spinlock.h> 16 #include <linux/spinlock.h>
16 #include <linux/atomic.h> 17 #include <linux/atomic.h>
17 #include <linux/err.h> 18 #include <linux/err.h>
18 #include <linux/cleanup.h> <<
19 <<
20 #ifdef CONFIG_DEBUG_LOCK_ALLOC <<
21 # define __RWSEM_DEP_MAP_INIT(lockname) <<
22 .dep_map = { <<
23 .name = #lockname, <<
24 .wait_type_inner = LD_WAIT_SLE <<
25 }, <<
26 #else <<
27 # define __RWSEM_DEP_MAP_INIT(lockname) <<
28 #endif <<
29 <<
30 #ifndef CONFIG_PREEMPT_RT <<
31 <<
32 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 19 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
33 #include <linux/osq_lock.h> 20 #include <linux/osq_lock.h>
34 #endif 21 #endif
35 22
36 /* 23 /*
37 * For an uncontended rwsem, count and owner a 24 * For an uncontended rwsem, count and owner are the only fields a task
38 * needs to touch when acquiring the rwsem. So 25 * needs to touch when acquiring the rwsem. So they are put next to each
39 * other to increase the chance that they will 26 * other to increase the chance that they will share the same cacheline.
40 * 27 *
41 * In a contended rwsem, the owner is likely t 28 * In a contended rwsem, the owner is likely the most frequently accessed
42 * field in the structure as the optimistic wa 29 * field in the structure as the optimistic waiter that holds the osq lock
43 * will spin on owner. For an embedded rwsem, 30 * will spin on owner. For an embedded rwsem, other hot fields in the
44 * containing structure should be moved furthe 31 * containing structure should be moved further away from the rwsem to
45 * reduce the chance that they will share the 32 * reduce the chance that they will share the same cacheline causing
46 * cacheline bouncing problem. 33 * cacheline bouncing problem.
47 */ 34 */
48 struct rw_semaphore { 35 struct rw_semaphore {
49 atomic_long_t count; 36 atomic_long_t count;
50 /* 37 /*
51 * Write owner or one of the read owne 38 * Write owner or one of the read owners as well flags regarding
52 * the current state of the rwsem. Can 39 * the current state of the rwsem. Can be used as a speculative
53 * check to see if the write owner is 40 * check to see if the write owner is running on the cpu.
54 */ 41 */
55 atomic_long_t owner; 42 atomic_long_t owner;
56 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 43 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
57 struct optimistic_spin_queue osq; /* s 44 struct optimistic_spin_queue osq; /* spinner MCS lock */
58 #endif 45 #endif
59 raw_spinlock_t wait_lock; 46 raw_spinlock_t wait_lock;
60 struct list_head wait_list; 47 struct list_head wait_list;
61 #ifdef CONFIG_DEBUG_RWSEMS 48 #ifdef CONFIG_DEBUG_RWSEMS
62 void *magic; 49 void *magic;
63 #endif 50 #endif
64 #ifdef CONFIG_DEBUG_LOCK_ALLOC 51 #ifdef CONFIG_DEBUG_LOCK_ALLOC
65 struct lockdep_map dep_map; 52 struct lockdep_map dep_map;
66 #endif 53 #endif
67 }; 54 };
68 55
69 #define RWSEM_UNLOCKED_VALUE 0UL !! 56 /* In all implementations count != 0 means locked */
70 #define RWSEM_WRITER_LOCKED (1UL < <<
71 #define __RWSEM_COUNT_INIT(name) .count <<
72 <<
73 static inline int rwsem_is_locked(struct rw_se 57 static inline int rwsem_is_locked(struct rw_semaphore *sem)
74 { 58 {
75 return atomic_long_read(&sem->count) ! !! 59 return atomic_long_read(&sem->count) != 0;
76 } 60 }
77 61
78 static inline void rwsem_assert_held_nolockdep !! 62 #define RWSEM_UNLOCKED_VALUE 0L
79 { !! 63 #define __RWSEM_COUNT_INIT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE)
80 WARN_ON(atomic_long_read(&sem->count) <<
81 } <<
82 <<
83 static inline void rwsem_assert_held_write_nol <<
84 { <<
85 WARN_ON(!(atomic_long_read(&sem->count <<
86 } <<
87 64
88 /* Common initializer macros and functions */ 65 /* Common initializer macros and functions */
89 66
>> 67 #ifdef CONFIG_DEBUG_LOCK_ALLOC
>> 68 # define __RWSEM_DEP_MAP_INIT(lockname) \
>> 69 .dep_map = { \
>> 70 .name = #lockname, \
>> 71 .wait_type_inner = LD_WAIT_SLEEP, \
>> 72 },
>> 73 #else
>> 74 # define __RWSEM_DEP_MAP_INIT(lockname)
>> 75 #endif
>> 76
90 #ifdef CONFIG_DEBUG_RWSEMS 77 #ifdef CONFIG_DEBUG_RWSEMS
91 # define __RWSEM_DEBUG_INIT(lockname) .magic = 78 # define __RWSEM_DEBUG_INIT(lockname) .magic = &lockname,
92 #else 79 #else
93 # define __RWSEM_DEBUG_INIT(lockname) 80 # define __RWSEM_DEBUG_INIT(lockname)
94 #endif 81 #endif
95 82
96 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 83 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
97 #define __RWSEM_OPT_INIT(lockname) .osq = OSQ_ 84 #define __RWSEM_OPT_INIT(lockname) .osq = OSQ_LOCK_UNLOCKED,
98 #else 85 #else
99 #define __RWSEM_OPT_INIT(lockname) 86 #define __RWSEM_OPT_INIT(lockname)
100 #endif 87 #endif
101 88
102 #define __RWSEM_INITIALIZER(name) 89 #define __RWSEM_INITIALIZER(name) \
103 { __RWSEM_COUNT_INIT(name), 90 { __RWSEM_COUNT_INIT(name), \
104 .owner = ATOMIC_LONG_INIT(0), 91 .owner = ATOMIC_LONG_INIT(0), \
105 __RWSEM_OPT_INIT(name) 92 __RWSEM_OPT_INIT(name) \
106 .wait_lock = __RAW_SPIN_LOCK_UNLOCKE 93 .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),\
107 .wait_list = LIST_HEAD_INIT((name).w 94 .wait_list = LIST_HEAD_INIT((name).wait_list), \
108 __RWSEM_DEBUG_INIT(name) 95 __RWSEM_DEBUG_INIT(name) \
109 __RWSEM_DEP_MAP_INIT(name) } 96 __RWSEM_DEP_MAP_INIT(name) }
110 97
111 #define DECLARE_RWSEM(name) \ 98 #define DECLARE_RWSEM(name) \
112 struct rw_semaphore name = __RWSEM_INI 99 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
113 100
114 extern void __init_rwsem(struct rw_semaphore * 101 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
115 struct lock_class_key 102 struct lock_class_key *key);
116 103
117 #define init_rwsem(sem) 104 #define init_rwsem(sem) \
118 do { 105 do { \
119 static struct lock_class_key __key; 106 static struct lock_class_key __key; \
120 107 \
121 __init_rwsem((sem), #sem, &__key); 108 __init_rwsem((sem), #sem, &__key); \
122 } while (0) 109 } while (0)
123 110
124 /* 111 /*
125 * This is the same regardless of which rwsem 112 * This is the same regardless of which rwsem implementation that is being used.
126 * It is just a heuristic meant to be called b !! 113 * It is just a heuristic meant to be called by somebody alreadying holding the
127 * rwsem to see if somebody from an incompatib 114 * rwsem to see if somebody from an incompatible type is wanting access to the
128 * lock. 115 * lock.
129 */ 116 */
130 static inline int rwsem_is_contended(struct rw 117 static inline int rwsem_is_contended(struct rw_semaphore *sem)
131 { 118 {
132 return !list_empty(&sem->wait_list); 119 return !list_empty(&sem->wait_list);
133 } 120 }
134 121
135 #else /* !CONFIG_PREEMPT_RT */ <<
136 <<
137 #include <linux/rwbase_rt.h> <<
138 <<
139 struct rw_semaphore { <<
140 struct rwbase_rt rwbase; <<
141 #ifdef CONFIG_DEBUG_LOCK_ALLOC <<
142 struct lockdep_map dep_map; <<
143 #endif <<
144 }; <<
145 <<
146 #define __RWSEM_INITIALIZER(name) <<
147 { <<
148 .rwbase = __RWBASE_INITIALIZER <<
149 __RWSEM_DEP_MAP_INIT(name) <<
150 } <<
151 <<
152 #define DECLARE_RWSEM(lockname) \ <<
153 struct rw_semaphore lockname = __RWSEM <<
154 <<
155 extern void __init_rwsem(struct rw_semaphore <<
156 struct lock_class_ke <<
157 <<
158 #define init_rwsem(sem) <<
159 do { <<
160 static struct lock_class_key __key; <<
161 <<
162 __init_rwsem((sem), #sem, &__key); <<
163 } while (0) <<
164 <<
165 static __always_inline int rwsem_is_locked(con <<
166 { <<
167 return rw_base_is_locked(&sem->rwbase) <<
168 } <<
169 <<
170 static __always_inline void rwsem_assert_held_ <<
171 { <<
172 WARN_ON(!rwsem_is_locked(sem)); <<
173 } <<
174 <<
175 static __always_inline void rwsem_assert_held_ <<
176 { <<
177 WARN_ON(!rw_base_is_write_locked(&sem- <<
178 } <<
179 <<
180 static __always_inline int rwsem_is_contended( <<
181 { <<
182 return rw_base_is_contended(&sem->rwba <<
183 } <<
184 <<
185 #endif /* CONFIG_PREEMPT_RT */ <<
186 <<
187 /* <<
188 * The functions below are the same for all rw <<
189 * the RT specific variant. <<
190 */ <<
191 <<
192 static inline void rwsem_assert_held(const str <<
193 { <<
194 if (IS_ENABLED(CONFIG_LOCKDEP)) <<
195 lockdep_assert_held(sem); <<
196 else <<
197 rwsem_assert_held_nolockdep(se <<
198 } <<
199 <<
200 static inline void rwsem_assert_held_write(con <<
201 { <<
202 if (IS_ENABLED(CONFIG_LOCKDEP)) <<
203 lockdep_assert_held_write(sem) <<
204 else <<
205 rwsem_assert_held_write_nolock <<
206 } <<
207 <<
208 /* 122 /*
209 * lock for reading 123 * lock for reading
210 */ 124 */
211 extern void down_read(struct rw_semaphore *sem 125 extern void down_read(struct rw_semaphore *sem);
212 extern int __must_check down_read_interruptibl 126 extern int __must_check down_read_interruptible(struct rw_semaphore *sem);
213 extern int __must_check down_read_killable(str 127 extern int __must_check down_read_killable(struct rw_semaphore *sem);
214 128
215 /* 129 /*
216 * trylock for reading -- returns 1 if success 130 * trylock for reading -- returns 1 if successful, 0 if contention
217 */ 131 */
218 extern int down_read_trylock(struct rw_semapho 132 extern int down_read_trylock(struct rw_semaphore *sem);
219 133
220 /* 134 /*
221 * lock for writing 135 * lock for writing
222 */ 136 */
223 extern void down_write(struct rw_semaphore *se 137 extern void down_write(struct rw_semaphore *sem);
224 extern int __must_check down_write_killable(st 138 extern int __must_check down_write_killable(struct rw_semaphore *sem);
225 139
226 /* 140 /*
227 * trylock for writing -- returns 1 if success 141 * trylock for writing -- returns 1 if successful, 0 if contention
228 */ 142 */
229 extern int down_write_trylock(struct rw_semaph 143 extern int down_write_trylock(struct rw_semaphore *sem);
230 144
231 /* 145 /*
232 * release a read lock 146 * release a read lock
233 */ 147 */
234 extern void up_read(struct rw_semaphore *sem); 148 extern void up_read(struct rw_semaphore *sem);
235 149
236 /* 150 /*
237 * release a write lock 151 * release a write lock
238 */ 152 */
239 extern void up_write(struct rw_semaphore *sem) 153 extern void up_write(struct rw_semaphore *sem);
240 154
241 DEFINE_GUARD(rwsem_read, struct rw_semaphore * <<
242 DEFINE_GUARD_COND(rwsem_read, _try, down_read_ <<
243 DEFINE_GUARD_COND(rwsem_read, _intr, down_read <<
244 <<
245 DEFINE_GUARD(rwsem_write, struct rw_semaphore <<
246 DEFINE_GUARD_COND(rwsem_write, _try, down_writ <<
247 <<
248 /* 155 /*
249 * downgrade write lock to read lock 156 * downgrade write lock to read lock
250 */ 157 */
251 extern void downgrade_write(struct rw_semaphor 158 extern void downgrade_write(struct rw_semaphore *sem);
252 159
253 #ifdef CONFIG_DEBUG_LOCK_ALLOC 160 #ifdef CONFIG_DEBUG_LOCK_ALLOC
254 /* 161 /*
255 * nested locking. NOTE: rwsems are not allowe 162 * nested locking. NOTE: rwsems are not allowed to recurse
256 * (which occurs if the same task tries to acq 163 * (which occurs if the same task tries to acquire the same
257 * lock instance multiple times), but multiple 164 * lock instance multiple times), but multiple locks of the
258 * same lock class might be taken, if the orde 165 * same lock class might be taken, if the order of the locks
259 * is always the same. This ordering rule can 166 * is always the same. This ordering rule can be expressed
260 * to lockdep via the _nested() APIs, but enum 167 * to lockdep via the _nested() APIs, but enumerating the
261 * subclasses that are used. (If the nesting r 168 * subclasses that are used. (If the nesting relationship is
262 * static then another method for expressing n 169 * static then another method for expressing nested locking is
263 * the explicit definition of lock class keys 170 * the explicit definition of lock class keys and the use of
264 * lockdep_set_class() at lock initialization 171 * lockdep_set_class() at lock initialization time.
265 * See Documentation/locking/lockdep-design.rs 172 * See Documentation/locking/lockdep-design.rst for more details.)
266 */ 173 */
267 extern void down_read_nested(struct rw_semapho 174 extern void down_read_nested(struct rw_semaphore *sem, int subclass);
268 extern int __must_check down_read_killable_nes 175 extern int __must_check down_read_killable_nested(struct rw_semaphore *sem, int subclass);
269 extern void down_write_nested(struct rw_semaph 176 extern void down_write_nested(struct rw_semaphore *sem, int subclass);
270 extern int down_write_killable_nested(struct r 177 extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
271 extern void _down_write_nest_lock(struct rw_se 178 extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
272 179
273 # define down_write_nest_lock(sem, nest_lock) 180 # define down_write_nest_lock(sem, nest_lock) \
274 do { 181 do { \
275 typecheck(struct lockdep_map *, &(nest 182 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
276 _down_write_nest_lock(sem, &(nest_lock 183 _down_write_nest_lock(sem, &(nest_lock)->dep_map); \
277 } while (0) !! 184 } while (0);
278 185
279 /* 186 /*
280 * Take/release a lock when not the owner will 187 * Take/release a lock when not the owner will release it.
281 * 188 *
282 * [ This API should be avoided as much as pos 189 * [ This API should be avoided as much as possible - the
283 * proper abstraction for this case is compl 190 * proper abstraction for this case is completions. ]
284 */ 191 */
285 extern void down_read_non_owner(struct rw_sema 192 extern void down_read_non_owner(struct rw_semaphore *sem);
286 extern void up_read_non_owner(struct rw_semaph 193 extern void up_read_non_owner(struct rw_semaphore *sem);
287 #else 194 #else
288 # define down_read_nested(sem, subclass) 195 # define down_read_nested(sem, subclass) down_read(sem)
289 # define down_read_killable_nested(sem, subcla 196 # define down_read_killable_nested(sem, subclass) down_read_killable(sem)
290 # define down_write_nest_lock(sem, nest_lock) 197 # define down_write_nest_lock(sem, nest_lock) down_write(sem)
291 # define down_write_nested(sem, subclass) 198 # define down_write_nested(sem, subclass) down_write(sem)
292 # define down_write_killable_nested(sem, subcl 199 # define down_write_killable_nested(sem, subclass) down_write_killable(sem)
293 # define down_read_non_owner(sem) 200 # define down_read_non_owner(sem) down_read(sem)
294 # define up_read_non_owner(sem) 201 # define up_read_non_owner(sem) up_read(sem)
295 #endif 202 #endif
296 203
297 #endif /* _LINUX_RWSEM_H */ 204 #endif /* _LINUX_RWSEM_H */
298 205
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