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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/cgroup.h> |
19 | #include <linux/fs.h> |
20 | #include <linux/uaccess.h> |
21 | #include <linux/freezer.h> |
22 | #include <linux/seq_file.h> |
23 | |
24 | enum freezer_state { |
25 | CGROUP_THAWED = 0, |
26 | CGROUP_FREEZING, |
27 | CGROUP_FROZEN, |
28 | }; |
29 | |
30 | struct freezer { |
31 | struct cgroup_subsys_state css; |
32 | enum freezer_state state; |
33 | spinlock_t lock; /* protects _writes_ to state */ |
34 | }; |
35 | |
36 | static inline struct freezer *cgroup_freezer( |
37 | struct cgroup *cgroup) |
38 | { |
39 | return container_of( |
40 | cgroup_subsys_state(cgroup, freezer_subsys_id), |
41 | struct freezer, css); |
42 | } |
43 | |
44 | static inline struct freezer *task_freezer(struct task_struct *task) |
45 | { |
46 | return container_of(task_subsys_state(task, freezer_subsys_id), |
47 | struct freezer, css); |
48 | } |
49 | |
50 | int cgroup_frozen(struct task_struct *task) |
51 | { |
52 | struct freezer *freezer; |
53 | enum freezer_state state; |
54 | |
55 | task_lock(task); |
56 | freezer = task_freezer(task); |
57 | state = freezer->state; |
58 | task_unlock(task); |
59 | |
60 | return state == CGROUP_FROZEN; |
61 | } |
62 | |
63 | /* |
64 | * cgroups_write_string() limits the size of freezer state strings to |
65 | * CGROUP_LOCAL_BUFFER_SIZE |
66 | */ |
67 | static const char *freezer_state_strs[] = { |
68 | "THAWED", |
69 | "FREEZING", |
70 | "FROZEN", |
71 | }; |
72 | |
73 | /* |
74 | * State diagram |
75 | * Transitions are caused by userspace writes to the freezer.state file. |
76 | * The values in parenthesis are state labels. The rest are edge labels. |
77 | * |
78 | * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN) |
79 | * ^ ^ | | |
80 | * | \_______THAWED_______/ | |
81 | * \__________________________THAWED____________/ |
82 | */ |
83 | |
84 | struct cgroup_subsys freezer_subsys; |
85 | |
86 | /* Locks taken and their ordering |
87 | * ------------------------------ |
88 | * css_set_lock |
89 | * cgroup_mutex (AKA cgroup_lock) |
90 | * task->alloc_lock (AKA task_lock) |
91 | * freezer->lock |
92 | * task->sighand->siglock |
93 | * |
94 | * cgroup code forces css_set_lock to be taken before task->alloc_lock |
95 | * |
96 | * freezer_create(), freezer_destroy(): |
97 | * cgroup_mutex [ by cgroup core ] |
98 | * |
99 | * can_attach(): |
100 | * cgroup_mutex |
101 | * |
102 | * cgroup_frozen(): |
103 | * task->alloc_lock (to get task's cgroup) |
104 | * |
105 | * freezer_fork() (preserving fork() performance means can't take cgroup_mutex): |
106 | * task->alloc_lock (to get task's cgroup) |
107 | * freezer->lock |
108 | * sighand->siglock (if the cgroup is freezing) |
109 | * |
110 | * freezer_read(): |
111 | * cgroup_mutex |
112 | * freezer->lock |
113 | * read_lock css_set_lock (cgroup iterator start) |
114 | * |
115 | * freezer_write() (freeze): |
116 | * cgroup_mutex |
117 | * freezer->lock |
118 | * read_lock css_set_lock (cgroup iterator start) |
119 | * sighand->siglock |
120 | * |
121 | * freezer_write() (unfreeze): |
122 | * cgroup_mutex |
123 | * freezer->lock |
124 | * read_lock css_set_lock (cgroup iterator start) |
125 | * task->alloc_lock (to prevent races with freeze_task()) |
126 | * sighand->siglock |
127 | */ |
128 | static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss, |
129 | struct cgroup *cgroup) |
130 | { |
131 | struct freezer *freezer; |
132 | |
133 | freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL); |
134 | if (!freezer) |
135 | return ERR_PTR(-ENOMEM); |
136 | |
137 | spin_lock_init(&freezer->lock); |
138 | freezer->state = CGROUP_THAWED; |
139 | return &freezer->css; |
140 | } |
141 | |
142 | static void freezer_destroy(struct cgroup_subsys *ss, |
143 | struct cgroup *cgroup) |
144 | { |
145 | kfree(cgroup_freezer(cgroup)); |
146 | } |
147 | |
148 | /* Task is frozen or will freeze immediately when next it gets woken */ |
149 | static bool is_task_frozen_enough(struct task_struct *task) |
150 | { |
151 | return frozen(task) || |
152 | (task_is_stopped_or_traced(task) && freezing(task)); |
153 | } |
154 | |
155 | /* |
156 | * The call to cgroup_lock() in the freezer.state write method prevents |
157 | * a write to that file racing against an attach, and hence the |
158 | * can_attach() result will remain valid until the attach completes. |
159 | */ |
160 | static int freezer_can_attach(struct cgroup_subsys *ss, |
161 | struct cgroup *new_cgroup, |
162 | struct task_struct *task, bool threadgroup) |
163 | { |
164 | struct freezer *freezer; |
165 | |
166 | /* |
167 | * Anything frozen can't move or be moved to/from. |
168 | * |
169 | * Since orig_freezer->state == FROZEN means that @task has been |
170 | * frozen, so it's sufficient to check the latter condition. |
171 | */ |
172 | |
173 | if (is_task_frozen_enough(task)) |
174 | return -EBUSY; |
175 | |
176 | freezer = cgroup_freezer(new_cgroup); |
177 | if (freezer->state == CGROUP_FROZEN) |
178 | return -EBUSY; |
179 | |
180 | if (threadgroup) { |
181 | struct task_struct *c; |
182 | |
183 | rcu_read_lock(); |
184 | list_for_each_entry_rcu(c, &task->thread_group, thread_group) { |
185 | if (is_task_frozen_enough(c)) { |
186 | rcu_read_unlock(); |
187 | return -EBUSY; |
188 | } |
189 | } |
190 | rcu_read_unlock(); |
191 | } |
192 | |
193 | return 0; |
194 | } |
195 | |
196 | static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) |
197 | { |
198 | struct freezer *freezer; |
199 | |
200 | /* |
201 | * No lock is needed, since the task isn't on tasklist yet, |
202 | * so it can't be moved to another cgroup, which means the |
203 | * freezer won't be removed and will be valid during this |
204 | * function call. |
205 | */ |
206 | freezer = task_freezer(task); |
207 | |
208 | /* |
209 | * The root cgroup is non-freezable, so we can skip the |
210 | * following check. |
211 | */ |
212 | if (!freezer->css.cgroup->parent) |
213 | return; |
214 | |
215 | spin_lock_irq(&freezer->lock); |
216 | BUG_ON(freezer->state == CGROUP_FROZEN); |
217 | |
218 | /* Locking avoids race with FREEZING -> THAWED transitions. */ |
219 | if (freezer->state == CGROUP_FREEZING) |
220 | freeze_task(task, true); |
221 | spin_unlock_irq(&freezer->lock); |
222 | } |
223 | |
224 | /* |
225 | * caller must hold freezer->lock |
226 | */ |
227 | static void update_freezer_state(struct cgroup *cgroup, |
228 | struct freezer *freezer) |
229 | { |
230 | struct cgroup_iter it; |
231 | struct task_struct *task; |
232 | unsigned int nfrozen = 0, ntotal = 0; |
233 | |
234 | cgroup_iter_start(cgroup, &it); |
235 | while ((task = cgroup_iter_next(cgroup, &it))) { |
236 | ntotal++; |
237 | if (is_task_frozen_enough(task)) |
238 | nfrozen++; |
239 | } |
240 | |
241 | /* |
242 | * Transition to FROZEN when no new tasks can be added ensures |
243 | * that we never exist in the FROZEN state while there are unfrozen |
244 | * tasks. |
245 | */ |
246 | if (nfrozen == ntotal) |
247 | freezer->state = CGROUP_FROZEN; |
248 | else if (nfrozen > 0) |
249 | freezer->state = CGROUP_FREEZING; |
250 | else |
251 | freezer->state = CGROUP_THAWED; |
252 | cgroup_iter_end(cgroup, &it); |
253 | } |
254 | |
255 | static int freezer_read(struct cgroup *cgroup, struct cftype *cft, |
256 | struct seq_file *m) |
257 | { |
258 | struct freezer *freezer; |
259 | enum freezer_state state; |
260 | |
261 | if (!cgroup_lock_live_group(cgroup)) |
262 | return -ENODEV; |
263 | |
264 | freezer = cgroup_freezer(cgroup); |
265 | spin_lock_irq(&freezer->lock); |
266 | state = freezer->state; |
267 | if (state == CGROUP_FREEZING) { |
268 | /* We change from FREEZING to FROZEN lazily if the cgroup was |
269 | * only partially frozen when we exitted write. */ |
270 | update_freezer_state(cgroup, freezer); |
271 | state = freezer->state; |
272 | } |
273 | spin_unlock_irq(&freezer->lock); |
274 | cgroup_unlock(); |
275 | |
276 | seq_puts(m, freezer_state_strs[state]); |
277 | seq_putc(m, '\n'); |
278 | return 0; |
279 | } |
280 | |
281 | static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
282 | { |
283 | struct cgroup_iter it; |
284 | struct task_struct *task; |
285 | unsigned int num_cant_freeze_now = 0; |
286 | |
287 | freezer->state = CGROUP_FREEZING; |
288 | cgroup_iter_start(cgroup, &it); |
289 | while ((task = cgroup_iter_next(cgroup, &it))) { |
290 | if (!freeze_task(task, true)) |
291 | continue; |
292 | if (is_task_frozen_enough(task)) |
293 | continue; |
294 | if (!freezing(task) && !freezer_should_skip(task)) |
295 | num_cant_freeze_now++; |
296 | } |
297 | cgroup_iter_end(cgroup, &it); |
298 | |
299 | return num_cant_freeze_now ? -EBUSY : 0; |
300 | } |
301 | |
302 | static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
303 | { |
304 | struct cgroup_iter it; |
305 | struct task_struct *task; |
306 | |
307 | cgroup_iter_start(cgroup, &it); |
308 | while ((task = cgroup_iter_next(cgroup, &it))) { |
309 | thaw_process(task); |
310 | } |
311 | cgroup_iter_end(cgroup, &it); |
312 | |
313 | freezer->state = CGROUP_THAWED; |
314 | } |
315 | |
316 | static int freezer_change_state(struct cgroup *cgroup, |
317 | enum freezer_state goal_state) |
318 | { |
319 | struct freezer *freezer; |
320 | int retval = 0; |
321 | |
322 | freezer = cgroup_freezer(cgroup); |
323 | |
324 | spin_lock_irq(&freezer->lock); |
325 | |
326 | update_freezer_state(cgroup, freezer); |
327 | if (goal_state == freezer->state) |
328 | goto out; |
329 | |
330 | switch (goal_state) { |
331 | case CGROUP_THAWED: |
332 | unfreeze_cgroup(cgroup, freezer); |
333 | break; |
334 | case CGROUP_FROZEN: |
335 | retval = try_to_freeze_cgroup(cgroup, freezer); |
336 | break; |
337 | default: |
338 | BUG(); |
339 | } |
340 | out: |
341 | spin_unlock_irq(&freezer->lock); |
342 | |
343 | return retval; |
344 | } |
345 | |
346 | static int freezer_write(struct cgroup *cgroup, |
347 | struct cftype *cft, |
348 | const char *buffer) |
349 | { |
350 | int retval; |
351 | enum freezer_state goal_state; |
352 | |
353 | if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0) |
354 | goal_state = CGROUP_THAWED; |
355 | else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0) |
356 | goal_state = CGROUP_FROZEN; |
357 | else |
358 | return -EINVAL; |
359 | |
360 | if (!cgroup_lock_live_group(cgroup)) |
361 | return -ENODEV; |
362 | retval = freezer_change_state(cgroup, goal_state); |
363 | cgroup_unlock(); |
364 | return retval; |
365 | } |
366 | |
367 | static struct cftype files[] = { |
368 | { |
369 | .name = "state", |
370 | .read_seq_string = freezer_read, |
371 | .write_string = freezer_write, |
372 | }, |
373 | }; |
374 | |
375 | static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup) |
376 | { |
377 | if (!cgroup->parent) |
378 | return 0; |
379 | return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files)); |
380 | } |
381 | |
382 | struct cgroup_subsys freezer_subsys = { |
383 | .name = "freezer", |
384 | .create = freezer_create, |
385 | .destroy = freezer_destroy, |
386 | .populate = freezer_populate, |
387 | .subsys_id = freezer_subsys_id, |
388 | .can_attach = freezer_can_attach, |
389 | .attach = NULL, |
390 | .fork = freezer_fork, |
391 | .exit = NULL, |
392 | }; |
393 |
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