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6#include <linux/rwsem.h>
7#include <linux/sched.h>
8#include <linux/init.h>
9#include <linux/module.h>
10
11
12
13
14void __init_rwsem(struct rw_semaphore *sem, const char *name,
15 struct lock_class_key *key)
16{
17#ifdef CONFIG_DEBUG_LOCK_ALLOC
18
19
20
21 debug_check_no_locks_freed((void *)sem, sizeof(*sem));
22 lockdep_init_map(&sem->dep_map, name, key, 0);
23#endif
24 sem->count = RWSEM_UNLOCKED_VALUE;
25 spin_lock_init(&sem->wait_lock);
26 INIT_LIST_HEAD(&sem->wait_list);
27}
28
29EXPORT_SYMBOL(__init_rwsem);
30
31struct rwsem_waiter {
32 struct list_head list;
33 struct task_struct *task;
34 unsigned int flags;
35#define RWSEM_WAITING_FOR_READ 0x00000001
36#define RWSEM_WAITING_FOR_WRITE 0x00000002
37};
38
39
40
41
42
43
44
45
46
47
48
49static inline struct rw_semaphore *
50__rwsem_do_wake(struct rw_semaphore *sem, int downgrading)
51{
52 struct rwsem_waiter *waiter;
53 struct task_struct *tsk;
54 struct list_head *next;
55 signed long oldcount, woken, loop;
56
57 if (downgrading)
58 goto dont_wake_writers;
59
60
61
62
63 try_again:
64 oldcount = rwsem_atomic_update(RWSEM_ACTIVE_BIAS, sem)
65 - RWSEM_ACTIVE_BIAS;
66 if (oldcount & RWSEM_ACTIVE_MASK)
67 goto undo;
68
69 waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
70
71
72
73
74
75 if (!(waiter->flags & RWSEM_WAITING_FOR_WRITE))
76 goto readers_only;
77
78
79
80
81
82 list_del(&waiter->list);
83 tsk = waiter->task;
84 smp_mb();
85 waiter->task = NULL;
86 wake_up_process(tsk);
87 put_task_struct(tsk);
88 goto out;
89
90
91 dont_wake_writers:
92 waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
93 if (waiter->flags & RWSEM_WAITING_FOR_WRITE)
94 goto out;
95
96
97
98
99
100
101 readers_only:
102 woken = 0;
103 do {
104 woken++;
105
106 if (waiter->list.next == &sem->wait_list)
107 break;
108
109 waiter = list_entry(waiter->list.next,
110 struct rwsem_waiter, list);
111
112 } while (waiter->flags & RWSEM_WAITING_FOR_READ);
113
114 loop = woken;
115 woken *= RWSEM_ACTIVE_BIAS - RWSEM_WAITING_BIAS;
116 if (!downgrading)
117
118 woken -= RWSEM_ACTIVE_BIAS;
119
120 rwsem_atomic_add(woken, sem);
121
122 next = sem->wait_list.next;
123 for (; loop > 0; loop--) {
124 waiter = list_entry(next, struct rwsem_waiter, list);
125 next = waiter->list.next;
126 tsk = waiter->task;
127 smp_mb();
128 waiter->task = NULL;
129 wake_up_process(tsk);
130 put_task_struct(tsk);
131 }
132
133 sem->wait_list.next = next;
134 next->prev = &sem->wait_list;
135
136 out:
137 return sem;
138
139
140 undo:
141 if (rwsem_atomic_update(-RWSEM_ACTIVE_BIAS, sem) != 0)
142 goto out;
143 goto try_again;
144}
145
146
147
148
149static struct rw_semaphore __sched *
150rwsem_down_failed_common(struct rw_semaphore *sem,
151 struct rwsem_waiter *waiter, signed long adjustment)
152{
153 struct task_struct *tsk = current;
154 signed long count;
155
156 set_task_state(tsk, TASK_UNINTERRUPTIBLE);
157
158
159 spin_lock_irq(&sem->wait_lock);
160 waiter->task = tsk;
161 get_task_struct(tsk);
162
163 list_add_tail(&waiter->list, &sem->wait_list);
164
165
166 count = rwsem_atomic_update(adjustment, sem);
167
168
169 if (!(count & RWSEM_ACTIVE_MASK))
170 sem = __rwsem_do_wake(sem, 0);
171
172 spin_unlock_irq(&sem->wait_lock);
173
174
175 for (;;) {
176 if (!waiter->task)
177 break;
178 schedule();
179 set_task_state(tsk, TASK_UNINTERRUPTIBLE);
180 }
181
182 tsk->state = TASK_RUNNING;
183
184 return sem;
185}
186
187
188
189
190asmregparm struct rw_semaphore __sched *
191rwsem_down_read_failed(struct rw_semaphore *sem)
192{
193 struct rwsem_waiter waiter;
194
195 waiter.flags = RWSEM_WAITING_FOR_READ;
196 rwsem_down_failed_common(sem, &waiter,
197 RWSEM_WAITING_BIAS - RWSEM_ACTIVE_BIAS);
198 return sem;
199}
200
201
202
203
204asmregparm struct rw_semaphore __sched *
205rwsem_down_write_failed(struct rw_semaphore *sem)
206{
207 struct rwsem_waiter waiter;
208
209 waiter.flags = RWSEM_WAITING_FOR_WRITE;
210 rwsem_down_failed_common(sem, &waiter, -RWSEM_ACTIVE_BIAS);
211
212 return sem;
213}
214
215
216
217
218
219asmregparm struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem)
220{
221 unsigned long flags;
222
223 spin_lock_irqsave(&sem->wait_lock, flags);
224
225
226 if (!list_empty(&sem->wait_list))
227 sem = __rwsem_do_wake(sem, 0);
228
229 spin_unlock_irqrestore(&sem->wait_lock, flags);
230
231 return sem;
232}
233
234
235
236
237
238
239asmregparm struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
240{
241 unsigned long flags;
242
243 spin_lock_irqsave(&sem->wait_lock, flags);
244
245
246 if (!list_empty(&sem->wait_list))
247 sem = __rwsem_do_wake(sem, 1);
248
249 spin_unlock_irqrestore(&sem->wait_lock, flags);
250
251 return sem;
252}
253
254EXPORT_SYMBOL(rwsem_down_read_failed);
255EXPORT_SYMBOL(rwsem_down_write_failed);
256EXPORT_SYMBOL(rwsem_wake);
257EXPORT_SYMBOL(rwsem_downgrade_wake);
258