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8#include <linux/rwsem.h>
9#include <linux/sched.h>
10#include <linux/module.h>
11
12struct rwsem_waiter {
13 struct list_head list;
14 struct task_struct *task;
15 unsigned int flags;
16#define RWSEM_WAITING_FOR_READ 0x00000001
17#define RWSEM_WAITING_FOR_WRITE 0x00000002
18};
19
20
21
22
23void __init_rwsem(struct rw_semaphore *sem, const char *name,
24 struct lock_class_key *key)
25{
26#ifdef CONFIG_DEBUG_LOCK_ALLOC
27
28
29
30 debug_check_no_locks_freed((void *)sem, sizeof(*sem));
31 lockdep_init_map(&sem->dep_map, name, key, 0);
32#endif
33 sem->activity = 0;
34 spin_lock_init(&sem->wait_lock);
35 INIT_LIST_HEAD(&sem->wait_list);
36}
37
38
39
40
41
42
43
44
45
46
47static inline struct rw_semaphore *
48__rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
49{
50 struct rwsem_waiter *waiter;
51 struct task_struct *tsk;
52 int woken;
53
54 waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
55
56 if (!wakewrite) {
57 if (waiter->flags & RWSEM_WAITING_FOR_WRITE)
58 goto out;
59 goto dont_wake_writers;
60 }
61
62
63
64
65
66
67 if (waiter->flags & RWSEM_WAITING_FOR_WRITE) {
68 sem->activity = -1;
69 list_del(&waiter->list);
70 tsk = waiter->task;
71
72 smp_mb();
73 waiter->task = NULL;
74 wake_up_process(tsk);
75 put_task_struct(tsk);
76 goto out;
77 }
78
79
80 dont_wake_writers:
81 woken = 0;
82 while (waiter->flags & RWSEM_WAITING_FOR_READ) {
83 struct list_head *next = waiter->list.next;
84
85 list_del(&waiter->list);
86 tsk = waiter->task;
87 smp_mb();
88 waiter->task = NULL;
89 wake_up_process(tsk);
90 put_task_struct(tsk);
91 woken++;
92 if (list_empty(&sem->wait_list))
93 break;
94 waiter = list_entry(next, struct rwsem_waiter, list);
95 }
96
97 sem->activity += woken;
98
99 out:
100 return sem;
101}
102
103
104
105
106static inline struct rw_semaphore *
107__rwsem_wake_one_writer(struct rw_semaphore *sem)
108{
109 struct rwsem_waiter *waiter;
110 struct task_struct *tsk;
111
112 sem->activity = -1;
113
114 waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
115 list_del(&waiter->list);
116
117 tsk = waiter->task;
118 smp_mb();
119 waiter->task = NULL;
120 wake_up_process(tsk);
121 put_task_struct(tsk);
122 return sem;
123}
124
125
126
127
128void __sched __down_read(struct rw_semaphore *sem)
129{
130 struct rwsem_waiter waiter;
131 struct task_struct *tsk;
132
133 spin_lock_irq(&sem->wait_lock);
134
135 if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
136
137 sem->activity++;
138 spin_unlock_irq(&sem->wait_lock);
139 goto out;
140 }
141
142 tsk = current;
143 set_task_state(tsk, TASK_UNINTERRUPTIBLE);
144
145
146 waiter.task = tsk;
147 waiter.flags = RWSEM_WAITING_FOR_READ;
148 get_task_struct(tsk);
149
150 list_add_tail(&waiter.list, &sem->wait_list);
151
152
153 spin_unlock_irq(&sem->wait_lock);
154
155
156 for (;;) {
157 if (!waiter.task)
158 break;
159 schedule();
160 set_task_state(tsk, TASK_UNINTERRUPTIBLE);
161 }
162
163 tsk->state = TASK_RUNNING;
164 out:
165 ;
166}
167
168
169
170
171int __down_read_trylock(struct rw_semaphore *sem)
172{
173 unsigned long flags;
174 int ret = 0;
175
176
177 spin_lock_irqsave(&sem->wait_lock, flags);
178
179 if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
180
181 sem->activity++;
182 ret = 1;
183 }
184
185 spin_unlock_irqrestore(&sem->wait_lock, flags);
186
187 return ret;
188}
189
190
191
192
193
194void __sched __down_write_nested(struct rw_semaphore *sem, int subclass)
195{
196 struct rwsem_waiter waiter;
197 struct task_struct *tsk;
198
199 spin_lock_irq(&sem->wait_lock);
200
201 if (sem->activity == 0 && list_empty(&sem->wait_list)) {
202
203 sem->activity = -1;
204 spin_unlock_irq(&sem->wait_lock);
205 goto out;
206 }
207
208 tsk = current;
209 set_task_state(tsk, TASK_UNINTERRUPTIBLE);
210
211
212 waiter.task = tsk;
213 waiter.flags = RWSEM_WAITING_FOR_WRITE;
214 get_task_struct(tsk);
215
216 list_add_tail(&waiter.list, &sem->wait_list);
217
218
219 spin_unlock_irq(&sem->wait_lock);
220
221
222 for (;;) {
223 if (!waiter.task)
224 break;
225 schedule();
226 set_task_state(tsk, TASK_UNINTERRUPTIBLE);
227 }
228
229 tsk->state = TASK_RUNNING;
230 out:
231 ;
232}
233
234void __sched __down_write(struct rw_semaphore *sem)
235{
236 __down_write_nested(sem, 0);
237}
238
239
240
241
242int __down_write_trylock(struct rw_semaphore *sem)
243{
244 unsigned long flags;
245 int ret = 0;
246
247 spin_lock_irqsave(&sem->wait_lock, flags);
248
249 if (sem->activity == 0 && list_empty(&sem->wait_list)) {
250
251 sem->activity = -1;
252 ret = 1;
253 }
254
255 spin_unlock_irqrestore(&sem->wait_lock, flags);
256
257 return ret;
258}
259
260
261
262
263void __up_read(struct rw_semaphore *sem)
264{
265 unsigned long flags;
266
267 spin_lock_irqsave(&sem->wait_lock, flags);
268
269 if (--sem->activity == 0 && !list_empty(&sem->wait_list))
270 sem = __rwsem_wake_one_writer(sem);
271
272 spin_unlock_irqrestore(&sem->wait_lock, flags);
273}
274
275
276
277
278void __up_write(struct rw_semaphore *sem)
279{
280 unsigned long flags;
281
282 spin_lock_irqsave(&sem->wait_lock, flags);
283
284 sem->activity = 0;
285 if (!list_empty(&sem->wait_list))
286 sem = __rwsem_do_wake(sem, 1);
287
288 spin_unlock_irqrestore(&sem->wait_lock, flags);
289}
290
291
292
293
294
295void __downgrade_write(struct rw_semaphore *sem)
296{
297 unsigned long flags;
298
299 spin_lock_irqsave(&sem->wait_lock, flags);
300
301 sem->activity = 1;
302 if (!list_empty(&sem->wait_list))
303 sem = __rwsem_do_wake(sem, 0);
304
305 spin_unlock_irqrestore(&sem->wait_lock, flags);
306}
307
308EXPORT_SYMBOL(__init_rwsem);
309EXPORT_SYMBOL(__down_read);
310EXPORT_SYMBOL(__down_read_trylock);
311EXPORT_SYMBOL(__down_write_nested);
312EXPORT_SYMBOL(__down_write);
313EXPORT_SYMBOL(__down_write_trylock);
314EXPORT_SYMBOL(__up_read);
315EXPORT_SYMBOL(__up_write);
316EXPORT_SYMBOL(__downgrade_write);
317