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Source at commit cdde9cf73945d547acd3e96f9508c79e84ad0bf1 created 12 years 9 months ago. By Maarten ter Huurne, MMC: JZ4740: Added support for CPU frequency changing | |
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1 | /* |
2 | * cgroup_freezer.c - control group freezer subsystem |
3 | * |
4 | * Copyright IBM Corporation, 2007 |
5 | * |
6 | * Author : Cedric Le Goater <clg@fr.ibm.com> |
7 | * |
8 | * This program is free software; you can redistribute it and/or modify it |
9 | * under the terms of version 2.1 of the GNU Lesser General Public License |
10 | * as published by the Free Software Foundation. |
11 | * |
12 | * This program is distributed in the hope that it would be useful, but |
13 | * WITHOUT ANY WARRANTY; without even the implied warranty of |
14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. |
15 | */ |
16 | |
17 | #include <linux/export.h> |
18 | #include <linux/slab.h> |
19 | #include <linux/cgroup.h> |
20 | #include <linux/fs.h> |
21 | #include <linux/uaccess.h> |
22 | #include <linux/freezer.h> |
23 | #include <linux/seq_file.h> |
24 | |
25 | enum freezer_state { |
26 | CGROUP_THAWED = 0, |
27 | CGROUP_FREEZING, |
28 | CGROUP_FROZEN, |
29 | }; |
30 | |
31 | struct freezer { |
32 | struct cgroup_subsys_state css; |
33 | enum freezer_state state; |
34 | spinlock_t lock; /* protects _writes_ to state */ |
35 | }; |
36 | |
37 | static inline struct freezer *cgroup_freezer( |
38 | struct cgroup *cgroup) |
39 | { |
40 | return container_of( |
41 | cgroup_subsys_state(cgroup, freezer_subsys_id), |
42 | struct freezer, css); |
43 | } |
44 | |
45 | static inline struct freezer *task_freezer(struct task_struct *task) |
46 | { |
47 | return container_of(task_subsys_state(task, freezer_subsys_id), |
48 | struct freezer, css); |
49 | } |
50 | |
51 | bool cgroup_freezing(struct task_struct *task) |
52 | { |
53 | enum freezer_state state; |
54 | bool ret; |
55 | |
56 | rcu_read_lock(); |
57 | state = task_freezer(task)->state; |
58 | ret = state == CGROUP_FREEZING || state == CGROUP_FROZEN; |
59 | rcu_read_unlock(); |
60 | |
61 | return ret; |
62 | } |
63 | |
64 | /* |
65 | * cgroups_write_string() limits the size of freezer state strings to |
66 | * CGROUP_LOCAL_BUFFER_SIZE |
67 | */ |
68 | static const char *freezer_state_strs[] = { |
69 | "THAWED", |
70 | "FREEZING", |
71 | "FROZEN", |
72 | }; |
73 | |
74 | /* |
75 | * State diagram |
76 | * Transitions are caused by userspace writes to the freezer.state file. |
77 | * The values in parenthesis are state labels. The rest are edge labels. |
78 | * |
79 | * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN) |
80 | * ^ ^ | | |
81 | * | \_______THAWED_______/ | |
82 | * \__________________________THAWED____________/ |
83 | */ |
84 | |
85 | struct cgroup_subsys freezer_subsys; |
86 | |
87 | /* Locks taken and their ordering |
88 | * ------------------------------ |
89 | * cgroup_mutex (AKA cgroup_lock) |
90 | * freezer->lock |
91 | * css_set_lock |
92 | * task->alloc_lock (AKA task_lock) |
93 | * task->sighand->siglock |
94 | * |
95 | * cgroup code forces css_set_lock to be taken before task->alloc_lock |
96 | * |
97 | * freezer_create(), freezer_destroy(): |
98 | * cgroup_mutex [ by cgroup core ] |
99 | * |
100 | * freezer_can_attach(): |
101 | * cgroup_mutex (held by caller of can_attach) |
102 | * |
103 | * freezer_fork() (preserving fork() performance means can't take cgroup_mutex): |
104 | * freezer->lock |
105 | * sighand->siglock (if the cgroup is freezing) |
106 | * |
107 | * freezer_read(): |
108 | * cgroup_mutex |
109 | * freezer->lock |
110 | * write_lock css_set_lock (cgroup iterator start) |
111 | * task->alloc_lock |
112 | * read_lock css_set_lock (cgroup iterator start) |
113 | * |
114 | * freezer_write() (freeze): |
115 | * cgroup_mutex |
116 | * freezer->lock |
117 | * write_lock css_set_lock (cgroup iterator start) |
118 | * task->alloc_lock |
119 | * read_lock css_set_lock (cgroup iterator start) |
120 | * sighand->siglock (fake signal delivery inside freeze_task()) |
121 | * |
122 | * freezer_write() (unfreeze): |
123 | * cgroup_mutex |
124 | * freezer->lock |
125 | * write_lock css_set_lock (cgroup iterator start) |
126 | * task->alloc_lock |
127 | * read_lock css_set_lock (cgroup iterator start) |
128 | * task->alloc_lock (inside __thaw_task(), prevents race with refrigerator()) |
129 | * sighand->siglock |
130 | */ |
131 | static struct cgroup_subsys_state *freezer_create(struct cgroup *cgroup) |
132 | { |
133 | struct freezer *freezer; |
134 | |
135 | freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL); |
136 | if (!freezer) |
137 | return ERR_PTR(-ENOMEM); |
138 | |
139 | spin_lock_init(&freezer->lock); |
140 | freezer->state = CGROUP_THAWED; |
141 | return &freezer->css; |
142 | } |
143 | |
144 | static void freezer_destroy(struct cgroup *cgroup) |
145 | { |
146 | struct freezer *freezer = cgroup_freezer(cgroup); |
147 | |
148 | if (freezer->state != CGROUP_THAWED) |
149 | atomic_dec(&system_freezing_cnt); |
150 | kfree(freezer); |
151 | } |
152 | |
153 | /* task is frozen or will freeze immediately when next it gets woken */ |
154 | static bool is_task_frozen_enough(struct task_struct *task) |
155 | { |
156 | return frozen(task) || |
157 | (task_is_stopped_or_traced(task) && freezing(task)); |
158 | } |
159 | |
160 | /* |
161 | * The call to cgroup_lock() in the freezer.state write method prevents |
162 | * a write to that file racing against an attach, and hence the |
163 | * can_attach() result will remain valid until the attach completes. |
164 | */ |
165 | static int freezer_can_attach(struct cgroup *new_cgroup, |
166 | struct cgroup_taskset *tset) |
167 | { |
168 | struct freezer *freezer; |
169 | struct task_struct *task; |
170 | |
171 | /* |
172 | * Anything frozen can't move or be moved to/from. |
173 | */ |
174 | cgroup_taskset_for_each(task, new_cgroup, tset) |
175 | if (cgroup_freezing(task)) |
176 | return -EBUSY; |
177 | |
178 | freezer = cgroup_freezer(new_cgroup); |
179 | if (freezer->state != CGROUP_THAWED) |
180 | return -EBUSY; |
181 | |
182 | return 0; |
183 | } |
184 | |
185 | static void freezer_fork(struct task_struct *task) |
186 | { |
187 | struct freezer *freezer; |
188 | |
189 | /* |
190 | * No lock is needed, since the task isn't on tasklist yet, |
191 | * so it can't be moved to another cgroup, which means the |
192 | * freezer won't be removed and will be valid during this |
193 | * function call. Nevertheless, apply RCU read-side critical |
194 | * section to suppress RCU lockdep false positives. |
195 | */ |
196 | rcu_read_lock(); |
197 | freezer = task_freezer(task); |
198 | rcu_read_unlock(); |
199 | |
200 | /* |
201 | * The root cgroup is non-freezable, so we can skip the |
202 | * following check. |
203 | */ |
204 | if (!freezer->css.cgroup->parent) |
205 | return; |
206 | |
207 | spin_lock_irq(&freezer->lock); |
208 | BUG_ON(freezer->state == CGROUP_FROZEN); |
209 | |
210 | /* Locking avoids race with FREEZING -> THAWED transitions. */ |
211 | if (freezer->state == CGROUP_FREEZING) |
212 | freeze_task(task); |
213 | spin_unlock_irq(&freezer->lock); |
214 | } |
215 | |
216 | /* |
217 | * caller must hold freezer->lock |
218 | */ |
219 | static void update_if_frozen(struct cgroup *cgroup, |
220 | struct freezer *freezer) |
221 | { |
222 | struct cgroup_iter it; |
223 | struct task_struct *task; |
224 | unsigned int nfrozen = 0, ntotal = 0; |
225 | enum freezer_state old_state = freezer->state; |
226 | |
227 | cgroup_iter_start(cgroup, &it); |
228 | while ((task = cgroup_iter_next(cgroup, &it))) { |
229 | ntotal++; |
230 | if (freezing(task) && is_task_frozen_enough(task)) |
231 | nfrozen++; |
232 | } |
233 | |
234 | if (old_state == CGROUP_THAWED) { |
235 | BUG_ON(nfrozen > 0); |
236 | } else if (old_state == CGROUP_FREEZING) { |
237 | if (nfrozen == ntotal) |
238 | freezer->state = CGROUP_FROZEN; |
239 | } else { /* old_state == CGROUP_FROZEN */ |
240 | BUG_ON(nfrozen != ntotal); |
241 | } |
242 | |
243 | cgroup_iter_end(cgroup, &it); |
244 | } |
245 | |
246 | static int freezer_read(struct cgroup *cgroup, struct cftype *cft, |
247 | struct seq_file *m) |
248 | { |
249 | struct freezer *freezer; |
250 | enum freezer_state state; |
251 | |
252 | if (!cgroup_lock_live_group(cgroup)) |
253 | return -ENODEV; |
254 | |
255 | freezer = cgroup_freezer(cgroup); |
256 | spin_lock_irq(&freezer->lock); |
257 | state = freezer->state; |
258 | if (state == CGROUP_FREEZING) { |
259 | /* We change from FREEZING to FROZEN lazily if the cgroup was |
260 | * only partially frozen when we exitted write. */ |
261 | update_if_frozen(cgroup, freezer); |
262 | state = freezer->state; |
263 | } |
264 | spin_unlock_irq(&freezer->lock); |
265 | cgroup_unlock(); |
266 | |
267 | seq_puts(m, freezer_state_strs[state]); |
268 | seq_putc(m, '\n'); |
269 | return 0; |
270 | } |
271 | |
272 | static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
273 | { |
274 | struct cgroup_iter it; |
275 | struct task_struct *task; |
276 | unsigned int num_cant_freeze_now = 0; |
277 | |
278 | cgroup_iter_start(cgroup, &it); |
279 | while ((task = cgroup_iter_next(cgroup, &it))) { |
280 | if (!freeze_task(task)) |
281 | continue; |
282 | if (is_task_frozen_enough(task)) |
283 | continue; |
284 | if (!freezing(task) && !freezer_should_skip(task)) |
285 | num_cant_freeze_now++; |
286 | } |
287 | cgroup_iter_end(cgroup, &it); |
288 | |
289 | return num_cant_freeze_now ? -EBUSY : 0; |
290 | } |
291 | |
292 | static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
293 | { |
294 | struct cgroup_iter it; |
295 | struct task_struct *task; |
296 | |
297 | cgroup_iter_start(cgroup, &it); |
298 | while ((task = cgroup_iter_next(cgroup, &it))) |
299 | __thaw_task(task); |
300 | cgroup_iter_end(cgroup, &it); |
301 | } |
302 | |
303 | static int freezer_change_state(struct cgroup *cgroup, |
304 | enum freezer_state goal_state) |
305 | { |
306 | struct freezer *freezer; |
307 | int retval = 0; |
308 | |
309 | freezer = cgroup_freezer(cgroup); |
310 | |
311 | spin_lock_irq(&freezer->lock); |
312 | |
313 | update_if_frozen(cgroup, freezer); |
314 | |
315 | switch (goal_state) { |
316 | case CGROUP_THAWED: |
317 | if (freezer->state != CGROUP_THAWED) |
318 | atomic_dec(&system_freezing_cnt); |
319 | freezer->state = CGROUP_THAWED; |
320 | unfreeze_cgroup(cgroup, freezer); |
321 | break; |
322 | case CGROUP_FROZEN: |
323 | if (freezer->state == CGROUP_THAWED) |
324 | atomic_inc(&system_freezing_cnt); |
325 | freezer->state = CGROUP_FREEZING; |
326 | retval = try_to_freeze_cgroup(cgroup, freezer); |
327 | break; |
328 | default: |
329 | BUG(); |
330 | } |
331 | |
332 | spin_unlock_irq(&freezer->lock); |
333 | |
334 | return retval; |
335 | } |
336 | |
337 | static int freezer_write(struct cgroup *cgroup, |
338 | struct cftype *cft, |
339 | const char *buffer) |
340 | { |
341 | int retval; |
342 | enum freezer_state goal_state; |
343 | |
344 | if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0) |
345 | goal_state = CGROUP_THAWED; |
346 | else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0) |
347 | goal_state = CGROUP_FROZEN; |
348 | else |
349 | return -EINVAL; |
350 | |
351 | if (!cgroup_lock_live_group(cgroup)) |
352 | return -ENODEV; |
353 | retval = freezer_change_state(cgroup, goal_state); |
354 | cgroup_unlock(); |
355 | return retval; |
356 | } |
357 | |
358 | static struct cftype files[] = { |
359 | { |
360 | .name = "state", |
361 | .flags = CFTYPE_NOT_ON_ROOT, |
362 | .read_seq_string = freezer_read, |
363 | .write_string = freezer_write, |
364 | }, |
365 | { } /* terminate */ |
366 | }; |
367 | |
368 | struct cgroup_subsys freezer_subsys = { |
369 | .name = "freezer", |
370 | .create = freezer_create, |
371 | .destroy = freezer_destroy, |
372 | .subsys_id = freezer_subsys_id, |
373 | .can_attach = freezer_can_attach, |
374 | .fork = freezer_fork, |
375 | .base_cftypes = files, |
376 | }; |
377 |
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Tags:
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