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dc52ddc0 MH |
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> | |
5a0e3ad6 | 18 | #include <linux/slab.h> |
dc52ddc0 MH |
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 { | |
81dcf33c MH |
26 | CGROUP_THAWED = 0, |
27 | CGROUP_FREEZING, | |
28 | CGROUP_FROZEN, | |
dc52ddc0 MH |
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 | ||
5a7aadfe | 51 | int cgroup_freezing_or_frozen(struct task_struct *task) |
dc52ddc0 MH |
52 | { |
53 | struct freezer *freezer; | |
54 | enum freezer_state state; | |
55 | ||
56 | task_lock(task); | |
57 | freezer = task_freezer(task); | |
5a7aadfe MH |
58 | if (!freezer->css.cgroup->parent) |
59 | state = CGROUP_THAWED; /* root cgroup can't be frozen */ | |
60 | else | |
61 | state = freezer->state; | |
dc52ddc0 MH |
62 | task_unlock(task); |
63 | ||
5a7aadfe | 64 | return (state == CGROUP_FREEZING) || (state == CGROUP_FROZEN); |
dc52ddc0 MH |
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[] = { | |
81dcf33c | 72 | "THAWED", |
dc52ddc0 MH |
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 | * | |
81dcf33c MH |
82 | * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN) |
83 | * ^ ^ | | | |
84 | * | \_______THAWED_______/ | | |
85 | * \__________________________THAWED____________/ | |
dc52ddc0 MH |
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); | |
81dcf33c | 142 | freezer->state = CGROUP_THAWED; |
dc52ddc0 MH |
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 | ||
957a4eea MH |
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 | } | |
dc52ddc0 | 158 | |
957a4eea MH |
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 | */ | |
dc52ddc0 MH |
164 | static int freezer_can_attach(struct cgroup_subsys *ss, |
165 | struct cgroup *new_cgroup, | |
be367d09 | 166 | struct task_struct *task, bool threadgroup) |
dc52ddc0 MH |
167 | { |
168 | struct freezer *freezer; | |
957a4eea | 169 | |
80a6a2cf LZ |
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 | */ | |
957a4eea MH |
176 | |
177 | if (is_task_frozen_enough(task)) | |
178 | return -EBUSY; | |
dc52ddc0 | 179 | |
dc52ddc0 | 180 | freezer = cgroup_freezer(new_cgroup); |
81dcf33c | 181 | if (freezer->state == CGROUP_FROZEN) |
957a4eea MH |
182 | return -EBUSY; |
183 | ||
be367d09 BB |
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 | ||
80a6a2cf | 197 | return 0; |
dc52ddc0 MH |
198 | } |
199 | ||
200 | static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) | |
201 | { | |
202 | struct freezer *freezer; | |
203 | ||
68744676 LZ |
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 | */ | |
dc52ddc0 | 210 | freezer = task_freezer(task); |
dc52ddc0 | 211 | |
3b1b3f6e LZ |
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 | ||
dc52ddc0 | 219 | spin_lock_irq(&freezer->lock); |
7ccb9743 LZ |
220 | BUG_ON(freezer->state == CGROUP_FROZEN); |
221 | ||
81dcf33c MH |
222 | /* Locking avoids race with FREEZING -> THAWED transitions. */ |
223 | if (freezer->state == CGROUP_FREEZING) | |
dc52ddc0 MH |
224 | freeze_task(task, true); |
225 | spin_unlock_irq(&freezer->lock); | |
226 | } | |
227 | ||
228 | /* | |
229 | * caller must hold freezer->lock | |
230 | */ | |
1aece348 MH |
231 | static void update_freezer_state(struct cgroup *cgroup, |
232 | struct freezer *freezer) | |
dc52ddc0 MH |
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++; | |
957a4eea | 241 | if (is_task_frozen_enough(task)) |
dc52ddc0 MH |
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) | |
81dcf33c | 251 | freezer->state = CGROUP_FROZEN; |
1aece348 MH |
252 | else if (nfrozen > 0) |
253 | freezer->state = CGROUP_FREEZING; | |
254 | else | |
255 | freezer->state = CGROUP_THAWED; | |
dc52ddc0 MH |
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; | |
81dcf33c | 271 | if (state == CGROUP_FREEZING) { |
dc52ddc0 MH |
272 | /* We change from FREEZING to FROZEN lazily if the cgroup was |
273 | * only partially frozen when we exitted write. */ | |
1aece348 | 274 | update_freezer_state(cgroup, freezer); |
dc52ddc0 MH |
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 | ||
81dcf33c | 291 | freezer->state = CGROUP_FREEZING; |
dc52ddc0 MH |
292 | cgroup_iter_start(cgroup, &it); |
293 | while ((task = cgroup_iter_next(cgroup, &it))) { | |
294 | if (!freeze_task(task, true)) | |
295 | continue; | |
957a4eea | 296 | if (is_task_frozen_enough(task)) |
dc52ddc0 MH |
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 | ||
00c2e63c | 306 | static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
dc52ddc0 MH |
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))) { | |
00c2e63c | 313 | thaw_process(task); |
dc52ddc0 MH |
314 | } |
315 | cgroup_iter_end(cgroup, &it); | |
dc52ddc0 | 316 | |
00c2e63c | 317 | freezer->state = CGROUP_THAWED; |
dc52ddc0 MH |
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); | |
51308ee5 | 327 | |
dc52ddc0 | 328 | spin_lock_irq(&freezer->lock); |
51308ee5 | 329 | |
1aece348 | 330 | update_freezer_state(cgroup, freezer); |
dc52ddc0 MH |
331 | if (goal_state == freezer->state) |
332 | goto out; | |
51308ee5 LZ |
333 | |
334 | switch (goal_state) { | |
81dcf33c | 335 | case CGROUP_THAWED: |
51308ee5 | 336 | unfreeze_cgroup(cgroup, freezer); |
dc52ddc0 | 337 | break; |
81dcf33c | 338 | case CGROUP_FROZEN: |
51308ee5 | 339 | retval = try_to_freeze_cgroup(cgroup, freezer); |
dc52ddc0 MH |
340 | break; |
341 | default: | |
51308ee5 | 342 | BUG(); |
dc52ddc0 MH |
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 | ||
81dcf33c MH |
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; | |
dc52ddc0 | 361 | else |
3b1b3f6e | 362 | return -EINVAL; |
dc52ddc0 MH |
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 | { | |
3b1b3f6e LZ |
381 | if (!cgroup->parent) |
382 | return 0; | |
dc52ddc0 MH |
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 | }; |