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