Contents of /alx-src/tags/kernel26-2.6.12-alx-r9/lib/rwsem-spinlock.c
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Wed Mar 4 11:03:09 2009 UTC (15 years, 3 months ago) by niro
File MIME type: text/plain
File size: 7665 byte(s)
Wed Mar 4 11:03:09 2009 UTC (15 years, 3 months ago) by niro
File MIME type: text/plain
File size: 7665 byte(s)
Tag kernel26-2.6.12-alx-r9
1 | /* rwsem-spinlock.c: R/W semaphores: contention handling functions for |
2 | * generic spinlock implementation |
3 | * |
4 | * Copyright (c) 2001 David Howells (dhowells@redhat.com). |
5 | * - Derived partially from idea by Andrea Arcangeli <andrea@suse.de> |
6 | * - Derived also from comments by Linus |
7 | */ |
8 | #include <linux/rwsem.h> |
9 | #include <linux/sched.h> |
10 | #include <linux/module.h> |
11 | |
12 | struct 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 | #if RWSEM_DEBUG |
21 | void rwsemtrace(struct rw_semaphore *sem, const char *str) |
22 | { |
23 | if (sem->debug) |
24 | printk("[%d] %s({%d,%d})\n", |
25 | current->pid, str, sem->activity, |
26 | list_empty(&sem->wait_list) ? 0 : 1); |
27 | } |
28 | #endif |
29 | |
30 | /* |
31 | * initialise the semaphore |
32 | */ |
33 | void fastcall init_rwsem(struct rw_semaphore *sem) |
34 | { |
35 | sem->activity = 0; |
36 | spin_lock_init(&sem->wait_lock); |
37 | INIT_LIST_HEAD(&sem->wait_list); |
38 | #if RWSEM_DEBUG |
39 | sem->debug = 0; |
40 | #endif |
41 | } |
42 | |
43 | /* |
44 | * handle the lock release when processes blocked on it that can now run |
45 | * - if we come here, then: |
46 | * - the 'active count' _reached_ zero |
47 | * - the 'waiting count' is non-zero |
48 | * - the spinlock must be held by the caller |
49 | * - woken process blocks are discarded from the list after having task zeroed |
50 | * - writers are only woken if wakewrite is non-zero |
51 | */ |
52 | static inline struct rw_semaphore * |
53 | __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite) |
54 | { |
55 | struct rwsem_waiter *waiter; |
56 | struct task_struct *tsk; |
57 | int woken; |
58 | |
59 | rwsemtrace(sem, "Entering __rwsem_do_wake"); |
60 | |
61 | waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); |
62 | |
63 | if (!wakewrite) { |
64 | if (waiter->flags & RWSEM_WAITING_FOR_WRITE) |
65 | goto out; |
66 | goto dont_wake_writers; |
67 | } |
68 | |
69 | /* if we are allowed to wake writers try to grant a single write lock |
70 | * if there's a writer at the front of the queue |
71 | * - we leave the 'waiting count' incremented to signify potential |
72 | * contention |
73 | */ |
74 | if (waiter->flags & RWSEM_WAITING_FOR_WRITE) { |
75 | sem->activity = -1; |
76 | list_del(&waiter->list); |
77 | tsk = waiter->task; |
78 | /* Don't touch waiter after ->task has been NULLed */ |
79 | smp_mb(); |
80 | waiter->task = NULL; |
81 | wake_up_process(tsk); |
82 | put_task_struct(tsk); |
83 | goto out; |
84 | } |
85 | |
86 | /* grant an infinite number of read locks to the front of the queue */ |
87 | dont_wake_writers: |
88 | woken = 0; |
89 | while (waiter->flags & RWSEM_WAITING_FOR_READ) { |
90 | struct list_head *next = waiter->list.next; |
91 | |
92 | list_del(&waiter->list); |
93 | tsk = waiter->task; |
94 | smp_mb(); |
95 | waiter->task = NULL; |
96 | wake_up_process(tsk); |
97 | put_task_struct(tsk); |
98 | woken++; |
99 | if (list_empty(&sem->wait_list)) |
100 | break; |
101 | waiter = list_entry(next, struct rwsem_waiter, list); |
102 | } |
103 | |
104 | sem->activity += woken; |
105 | |
106 | out: |
107 | rwsemtrace(sem, "Leaving __rwsem_do_wake"); |
108 | return sem; |
109 | } |
110 | |
111 | /* |
112 | * wake a single writer |
113 | */ |
114 | static inline struct rw_semaphore * |
115 | __rwsem_wake_one_writer(struct rw_semaphore *sem) |
116 | { |
117 | struct rwsem_waiter *waiter; |
118 | struct task_struct *tsk; |
119 | |
120 | sem->activity = -1; |
121 | |
122 | waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); |
123 | list_del(&waiter->list); |
124 | |
125 | tsk = waiter->task; |
126 | smp_mb(); |
127 | waiter->task = NULL; |
128 | wake_up_process(tsk); |
129 | put_task_struct(tsk); |
130 | return sem; |
131 | } |
132 | |
133 | /* |
134 | * get a read lock on the semaphore |
135 | */ |
136 | void fastcall __sched __down_read(struct rw_semaphore *sem) |
137 | { |
138 | struct rwsem_waiter waiter; |
139 | struct task_struct *tsk; |
140 | |
141 | rwsemtrace(sem, "Entering __down_read"); |
142 | |
143 | spin_lock_irq(&sem->wait_lock); |
144 | |
145 | if (sem->activity >= 0 && list_empty(&sem->wait_list)) { |
146 | /* granted */ |
147 | sem->activity++; |
148 | spin_unlock_irq(&sem->wait_lock); |
149 | goto out; |
150 | } |
151 | |
152 | tsk = current; |
153 | set_task_state(tsk, TASK_UNINTERRUPTIBLE); |
154 | |
155 | /* set up my own style of waitqueue */ |
156 | waiter.task = tsk; |
157 | waiter.flags = RWSEM_WAITING_FOR_READ; |
158 | get_task_struct(tsk); |
159 | |
160 | list_add_tail(&waiter.list, &sem->wait_list); |
161 | |
162 | /* we don't need to touch the semaphore struct anymore */ |
163 | spin_unlock_irq(&sem->wait_lock); |
164 | |
165 | /* wait to be given the lock */ |
166 | for (;;) { |
167 | if (!waiter.task) |
168 | break; |
169 | schedule(); |
170 | set_task_state(tsk, TASK_UNINTERRUPTIBLE); |
171 | } |
172 | |
173 | tsk->state = TASK_RUNNING; |
174 | |
175 | out: |
176 | rwsemtrace(sem, "Leaving __down_read"); |
177 | } |
178 | |
179 | /* |
180 | * trylock for reading -- returns 1 if successful, 0 if contention |
181 | */ |
182 | int fastcall __down_read_trylock(struct rw_semaphore *sem) |
183 | { |
184 | unsigned long flags; |
185 | int ret = 0; |
186 | |
187 | rwsemtrace(sem, "Entering __down_read_trylock"); |
188 | |
189 | spin_lock_irqsave(&sem->wait_lock, flags); |
190 | |
191 | if (sem->activity >= 0 && list_empty(&sem->wait_list)) { |
192 | /* granted */ |
193 | sem->activity++; |
194 | ret = 1; |
195 | } |
196 | |
197 | spin_unlock_irqrestore(&sem->wait_lock, flags); |
198 | |
199 | rwsemtrace(sem, "Leaving __down_read_trylock"); |
200 | return ret; |
201 | } |
202 | |
203 | /* |
204 | * get a write lock on the semaphore |
205 | * - we increment the waiting count anyway to indicate an exclusive lock |
206 | */ |
207 | void fastcall __sched __down_write(struct rw_semaphore *sem) |
208 | { |
209 | struct rwsem_waiter waiter; |
210 | struct task_struct *tsk; |
211 | |
212 | rwsemtrace(sem, "Entering __down_write"); |
213 | |
214 | spin_lock_irq(&sem->wait_lock); |
215 | |
216 | if (sem->activity == 0 && list_empty(&sem->wait_list)) { |
217 | /* granted */ |
218 | sem->activity = -1; |
219 | spin_unlock_irq(&sem->wait_lock); |
220 | goto out; |
221 | } |
222 | |
223 | tsk = current; |
224 | set_task_state(tsk, TASK_UNINTERRUPTIBLE); |
225 | |
226 | /* set up my own style of waitqueue */ |
227 | waiter.task = tsk; |
228 | waiter.flags = RWSEM_WAITING_FOR_WRITE; |
229 | get_task_struct(tsk); |
230 | |
231 | list_add_tail(&waiter.list, &sem->wait_list); |
232 | |
233 | /* we don't need to touch the semaphore struct anymore */ |
234 | spin_unlock_irq(&sem->wait_lock); |
235 | |
236 | /* wait to be given the lock */ |
237 | for (;;) { |
238 | if (!waiter.task) |
239 | break; |
240 | schedule(); |
241 | set_task_state(tsk, TASK_UNINTERRUPTIBLE); |
242 | } |
243 | |
244 | tsk->state = TASK_RUNNING; |
245 | |
246 | out: |
247 | rwsemtrace(sem, "Leaving __down_write"); |
248 | } |
249 | |
250 | /* |
251 | * trylock for writing -- returns 1 if successful, 0 if contention |
252 | */ |
253 | int fastcall __down_write_trylock(struct rw_semaphore *sem) |
254 | { |
255 | unsigned long flags; |
256 | int ret = 0; |
257 | |
258 | rwsemtrace(sem, "Entering __down_write_trylock"); |
259 | |
260 | spin_lock_irqsave(&sem->wait_lock, flags); |
261 | |
262 | if (sem->activity == 0 && list_empty(&sem->wait_list)) { |
263 | /* granted */ |
264 | sem->activity = -1; |
265 | ret = 1; |
266 | } |
267 | |
268 | spin_unlock_irqrestore(&sem->wait_lock, flags); |
269 | |
270 | rwsemtrace(sem, "Leaving __down_write_trylock"); |
271 | return ret; |
272 | } |
273 | |
274 | /* |
275 | * release a read lock on the semaphore |
276 | */ |
277 | void fastcall __up_read(struct rw_semaphore *sem) |
278 | { |
279 | unsigned long flags; |
280 | |
281 | rwsemtrace(sem, "Entering __up_read"); |
282 | |
283 | spin_lock_irqsave(&sem->wait_lock, flags); |
284 | |
285 | if (--sem->activity == 0 && !list_empty(&sem->wait_list)) |
286 | sem = __rwsem_wake_one_writer(sem); |
287 | |
288 | spin_unlock_irqrestore(&sem->wait_lock, flags); |
289 | |
290 | rwsemtrace(sem, "Leaving __up_read"); |
291 | } |
292 | |
293 | /* |
294 | * release a write lock on the semaphore |
295 | */ |
296 | void fastcall __up_write(struct rw_semaphore *sem) |
297 | { |
298 | unsigned long flags; |
299 | |
300 | rwsemtrace(sem, "Entering __up_write"); |
301 | |
302 | spin_lock_irqsave(&sem->wait_lock, flags); |
303 | |
304 | sem->activity = 0; |
305 | if (!list_empty(&sem->wait_list)) |
306 | sem = __rwsem_do_wake(sem, 1); |
307 | |
308 | spin_unlock_irqrestore(&sem->wait_lock, flags); |
309 | |
310 | rwsemtrace(sem, "Leaving __up_write"); |
311 | } |
312 | |
313 | /* |
314 | * downgrade a write lock into a read lock |
315 | * - just wake up any readers at the front of the queue |
316 | */ |
317 | void fastcall __downgrade_write(struct rw_semaphore *sem) |
318 | { |
319 | unsigned long flags; |
320 | |
321 | rwsemtrace(sem, "Entering __downgrade_write"); |
322 | |
323 | spin_lock_irqsave(&sem->wait_lock, flags); |
324 | |
325 | sem->activity = 1; |
326 | if (!list_empty(&sem->wait_list)) |
327 | sem = __rwsem_do_wake(sem, 0); |
328 | |
329 | spin_unlock_irqrestore(&sem->wait_lock, flags); |
330 | |
331 | rwsemtrace(sem, "Leaving __downgrade_write"); |
332 | } |
333 | |
334 | EXPORT_SYMBOL(init_rwsem); |
335 | EXPORT_SYMBOL(__down_read); |
336 | EXPORT_SYMBOL(__down_read_trylock); |
337 | EXPORT_SYMBOL(__down_write); |
338 | EXPORT_SYMBOL(__down_write_trylock); |
339 | EXPORT_SYMBOL(__up_read); |
340 | EXPORT_SYMBOL(__up_write); |
341 | EXPORT_SYMBOL(__downgrade_write); |
342 | #if RWSEM_DEBUG |
343 | EXPORT_SYMBOL(rwsemtrace); |
344 | #endif |