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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/module.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 | int cgroup_freezing_or_frozen(struct task_struct *task) |
52 | { |
53 | struct freezer *freezer; |
54 | enum freezer_state state; |
55 | |
56 | task_lock(task); |
57 | freezer = task_freezer(task); |
58 | if (!freezer->css.cgroup->parent) |
59 | state = CGROUP_THAWED; /* root cgroup can't be frozen */ |
60 | else |
61 | state = freezer->state; |
62 | task_unlock(task); |
63 | |
64 | return (state == CGROUP_FREEZING) || (state == CGROUP_FROZEN); |
65 | } |
66 | |
67 | /* |
68 | * cgroups_write_string() limits the size of freezer state strings to |
69 | * CGROUP_LOCAL_BUFFER_SIZE |
70 | */ |
71 | static const char *freezer_state_strs[] = { |
72 | "THAWED", |
73 | "FREEZING", |
74 | "FROZEN", |
75 | }; |
76 | |
77 | /* |
78 | * State diagram |
79 | * Transitions are caused by userspace writes to the freezer.state file. |
80 | * The values in parenthesis are state labels. The rest are edge labels. |
81 | * |
82 | * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN) |
83 | * ^ ^ | | |
84 | * | \_______THAWED_______/ | |
85 | * \__________________________THAWED____________/ |
86 | */ |
87 | |
88 | struct cgroup_subsys freezer_subsys; |
89 | |
90 | /* Locks taken and their ordering |
91 | * ------------------------------ |
92 | * css_set_lock |
93 | * cgroup_mutex (AKA cgroup_lock) |
94 | * task->alloc_lock (AKA task_lock) |
95 | * freezer->lock |
96 | * task->sighand->siglock |
97 | * |
98 | * cgroup code forces css_set_lock to be taken before task->alloc_lock |
99 | * |
100 | * freezer_create(), freezer_destroy(): |
101 | * cgroup_mutex [ by cgroup core ] |
102 | * |
103 | * can_attach(): |
104 | * cgroup_mutex |
105 | * |
106 | * cgroup_frozen(): |
107 | * task->alloc_lock (to get task's cgroup) |
108 | * |
109 | * freezer_fork() (preserving fork() performance means can't take cgroup_mutex): |
110 | * task->alloc_lock (to get task's cgroup) |
111 | * freezer->lock |
112 | * sighand->siglock (if the cgroup is freezing) |
113 | * |
114 | * freezer_read(): |
115 | * cgroup_mutex |
116 | * freezer->lock |
117 | * read_lock css_set_lock (cgroup iterator start) |
118 | * |
119 | * freezer_write() (freeze): |
120 | * cgroup_mutex |
121 | * freezer->lock |
122 | * read_lock css_set_lock (cgroup iterator start) |
123 | * sighand->siglock |
124 | * |
125 | * freezer_write() (unfreeze): |
126 | * cgroup_mutex |
127 | * freezer->lock |
128 | * read_lock css_set_lock (cgroup iterator start) |
129 | * task->alloc_lock (to prevent races with freeze_task()) |
130 | * sighand->siglock |
131 | */ |
132 | static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss, |
133 | struct cgroup *cgroup) |
134 | { |
135 | struct freezer *freezer; |
136 | |
137 | freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL); |
138 | if (!freezer) |
139 | return ERR_PTR(-ENOMEM); |
140 | |
141 | spin_lock_init(&freezer->lock); |
142 | freezer->state = CGROUP_THAWED; |
143 | return &freezer->css; |
144 | } |
145 | |
146 | static void freezer_destroy(struct cgroup_subsys *ss, |
147 | struct cgroup *cgroup) |
148 | { |
149 | kfree(cgroup_freezer(cgroup)); |
150 | } |
151 | |
152 | /* Task is frozen or will freeze immediately when next it gets woken */ |
153 | static bool is_task_frozen_enough(struct task_struct *task) |
154 | { |
155 | return frozen(task) || |
156 | (task_is_stopped_or_traced(task) && freezing(task)); |
157 | } |
158 | |
159 | /* |
160 | * The call to cgroup_lock() in the freezer.state write method prevents |
161 | * a write to that file racing against an attach, and hence the |
162 | * can_attach() result will remain valid until the attach completes. |
163 | */ |
164 | static int freezer_can_attach(struct cgroup_subsys *ss, |
165 | struct cgroup *new_cgroup, |
166 | struct task_struct *task, bool threadgroup) |
167 | { |
168 | struct freezer *freezer; |
169 | |
170 | /* |
171 | * Anything frozen can't move or be moved to/from. |
172 | * |
173 | * Since orig_freezer->state == FROZEN means that @task has been |
174 | * frozen, so it's sufficient to check the latter condition. |
175 | */ |
176 | |
177 | if (is_task_frozen_enough(task)) |
178 | return -EBUSY; |
179 | |
180 | freezer = cgroup_freezer(new_cgroup); |
181 | if (freezer->state == CGROUP_FROZEN) |
182 | return -EBUSY; |
183 | |
184 | if (threadgroup) { |
185 | struct task_struct *c; |
186 | |
187 | rcu_read_lock(); |
188 | list_for_each_entry_rcu(c, &task->thread_group, thread_group) { |
189 | if (is_task_frozen_enough(c)) { |
190 | rcu_read_unlock(); |
191 | return -EBUSY; |
192 | } |
193 | } |
194 | rcu_read_unlock(); |
195 | } |
196 | |
197 | return 0; |
198 | } |
199 | |
200 | static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) |
201 | { |
202 | struct freezer *freezer; |
203 | |
204 | /* |
205 | * No lock is needed, since the task isn't on tasklist yet, |
206 | * so it can't be moved to another cgroup, which means the |
207 | * freezer won't be removed and will be valid during this |
208 | * function call. |
209 | */ |
210 | freezer = task_freezer(task); |
211 | |
212 | /* |
213 | * The root cgroup is non-freezable, so we can skip the |
214 | * following check. |
215 | */ |
216 | if (!freezer->css.cgroup->parent) |
217 | return; |
218 | |
219 | spin_lock_irq(&freezer->lock); |
220 | BUG_ON(freezer->state == CGROUP_FROZEN); |
221 | |
222 | /* Locking avoids race with FREEZING -> THAWED transitions. */ |
223 | if (freezer->state == CGROUP_FREEZING) |
224 | freeze_task(task, true); |
225 | spin_unlock_irq(&freezer->lock); |
226 | } |
227 | |
228 | /* |
229 | * caller must hold freezer->lock |
230 | */ |
231 | static void update_freezer_state(struct cgroup *cgroup, |
232 | struct freezer *freezer) |
233 | { |
234 | struct cgroup_iter it; |
235 | struct task_struct *task; |
236 | unsigned int nfrozen = 0, ntotal = 0; |
237 | |
238 | cgroup_iter_start(cgroup, &it); |
239 | while ((task = cgroup_iter_next(cgroup, &it))) { |
240 | ntotal++; |
241 | if (is_task_frozen_enough(task)) |
242 | nfrozen++; |
243 | } |
244 | |
245 | /* |
246 | * Transition to FROZEN when no new tasks can be added ensures |
247 | * that we never exist in the FROZEN state while there are unfrozen |
248 | * tasks. |
249 | */ |
250 | if (nfrozen == ntotal) |
251 | freezer->state = CGROUP_FROZEN; |
252 | else if (nfrozen > 0) |
253 | freezer->state = CGROUP_FREEZING; |
254 | else |
255 | freezer->state = CGROUP_THAWED; |
256 | cgroup_iter_end(cgroup, &it); |
257 | } |
258 | |
259 | static int freezer_read(struct cgroup *cgroup, struct cftype *cft, |
260 | struct seq_file *m) |
261 | { |
262 | struct freezer *freezer; |
263 | enum freezer_state state; |
264 | |
265 | if (!cgroup_lock_live_group(cgroup)) |
266 | return -ENODEV; |
267 | |
268 | freezer = cgroup_freezer(cgroup); |
269 | spin_lock_irq(&freezer->lock); |
270 | state = freezer->state; |
271 | if (state == CGROUP_FREEZING) { |
272 | /* We change from FREEZING to FROZEN lazily if the cgroup was |
273 | * only partially frozen when we exitted write. */ |
274 | update_freezer_state(cgroup, freezer); |
275 | state = freezer->state; |
276 | } |
277 | spin_unlock_irq(&freezer->lock); |
278 | cgroup_unlock(); |
279 | |
280 | seq_puts(m, freezer_state_strs[state]); |
281 | seq_putc(m, '\n'); |
282 | return 0; |
283 | } |
284 | |
285 | static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
286 | { |
287 | struct cgroup_iter it; |
288 | struct task_struct *task; |
289 | unsigned int num_cant_freeze_now = 0; |
290 | |
291 | freezer->state = CGROUP_FREEZING; |
292 | cgroup_iter_start(cgroup, &it); |
293 | while ((task = cgroup_iter_next(cgroup, &it))) { |
294 | if (!freeze_task(task, true)) |
295 | continue; |
296 | if (is_task_frozen_enough(task)) |
297 | continue; |
298 | if (!freezing(task) && !freezer_should_skip(task)) |
299 | num_cant_freeze_now++; |
300 | } |
301 | cgroup_iter_end(cgroup, &it); |
302 | |
303 | return num_cant_freeze_now ? -EBUSY : 0; |
304 | } |
305 | |
306 | static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
307 | { |
308 | struct cgroup_iter it; |
309 | struct task_struct *task; |
310 | |
311 | cgroup_iter_start(cgroup, &it); |
312 | while ((task = cgroup_iter_next(cgroup, &it))) { |
313 | thaw_process(task); |
314 | } |
315 | cgroup_iter_end(cgroup, &it); |
316 | |
317 | freezer->state = CGROUP_THAWED; |
318 | } |
319 | |
320 | static int freezer_change_state(struct cgroup *cgroup, |
321 | enum freezer_state goal_state) |
322 | { |
323 | struct freezer *freezer; |
324 | int retval = 0; |
325 | |
326 | freezer = cgroup_freezer(cgroup); |
327 | |
328 | spin_lock_irq(&freezer->lock); |
329 | |
330 | update_freezer_state(cgroup, freezer); |
331 | if (goal_state == freezer->state) |
332 | goto out; |
333 | |
334 | switch (goal_state) { |
335 | case CGROUP_THAWED: |
336 | unfreeze_cgroup(cgroup, freezer); |
337 | break; |
338 | case CGROUP_FROZEN: |
339 | retval = try_to_freeze_cgroup(cgroup, freezer); |
340 | break; |
341 | default: |
342 | BUG(); |
343 | } |
344 | out: |
345 | spin_unlock_irq(&freezer->lock); |
346 | |
347 | return retval; |
348 | } |
349 | |
350 | static int freezer_write(struct cgroup *cgroup, |
351 | struct cftype *cft, |
352 | const char *buffer) |
353 | { |
354 | int retval; |
355 | enum freezer_state goal_state; |
356 | |
357 | if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0) |
358 | goal_state = CGROUP_THAWED; |
359 | else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0) |
360 | goal_state = CGROUP_FROZEN; |
361 | else |
362 | return -EINVAL; |
363 | |
364 | if (!cgroup_lock_live_group(cgroup)) |
365 | return -ENODEV; |
366 | retval = freezer_change_state(cgroup, goal_state); |
367 | cgroup_unlock(); |
368 | return retval; |
369 | } |
370 | |
371 | static struct cftype files[] = { |
372 | { |
373 | .name = "state", |
374 | .read_seq_string = freezer_read, |
375 | .write_string = freezer_write, |
376 | }, |
377 | }; |
378 | |
379 | static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup) |
380 | { |
381 | if (!cgroup->parent) |
382 | return 0; |
383 | return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files)); |
384 | } |
385 | |
386 | struct cgroup_subsys freezer_subsys = { |
387 | .name = "freezer", |
388 | .create = freezer_create, |
389 | .destroy = freezer_destroy, |
390 | .populate = freezer_populate, |
391 | .subsys_id = freezer_subsys_id, |
392 | .can_attach = freezer_can_attach, |
393 | .attach = NULL, |
394 | .fork = freezer_fork, |
395 | .exit = NULL, |
396 | }; |
397 |
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