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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 | ||
51 | int cgroup_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 | state = freezer->state; | |
59 | task_unlock(task); | |
60 | ||
81dcf33c | 61 | return state == CGROUP_FROZEN; |
dc52ddc0 MH |
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[] = { | |
81dcf33c | 69 | "THAWED", |
dc52ddc0 MH |
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 | * | |
81dcf33c MH |
79 | * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN) |
80 | * ^ ^ | | | |
81 | * | \_______THAWED_______/ | | |
82 | * \__________________________THAWED____________/ | |
dc52ddc0 MH |
83 | */ |
84 | ||
85 | struct cgroup_subsys freezer_subsys; | |
86 | ||
87 | /* Locks taken and their ordering | |
88 | * ------------------------------ | |
89 | * css_set_lock | |
90 | * cgroup_mutex (AKA cgroup_lock) | |
91 | * task->alloc_lock (AKA task_lock) | |
92 | * freezer->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 | * can_attach(): | |
101 | * cgroup_mutex | |
102 | * | |
103 | * cgroup_frozen(): | |
104 | * task->alloc_lock (to get task's cgroup) | |
105 | * | |
106 | * freezer_fork() (preserving fork() performance means can't take cgroup_mutex): | |
107 | * task->alloc_lock (to get task's cgroup) | |
108 | * freezer->lock | |
109 | * sighand->siglock (if the cgroup is freezing) | |
110 | * | |
111 | * freezer_read(): | |
112 | * cgroup_mutex | |
113 | * freezer->lock | |
114 | * read_lock css_set_lock (cgroup iterator start) | |
115 | * | |
116 | * freezer_write() (freeze): | |
117 | * cgroup_mutex | |
118 | * freezer->lock | |
119 | * read_lock css_set_lock (cgroup iterator start) | |
120 | * sighand->siglock | |
121 | * | |
122 | * freezer_write() (unfreeze): | |
123 | * cgroup_mutex | |
124 | * freezer->lock | |
125 | * read_lock css_set_lock (cgroup iterator start) | |
126 | * task->alloc_lock (to prevent races with freeze_task()) | |
127 | * sighand->siglock | |
128 | */ | |
129 | static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss, | |
130 | struct cgroup *cgroup) | |
131 | { | |
132 | struct freezer *freezer; | |
133 | ||
134 | freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL); | |
135 | if (!freezer) | |
136 | return ERR_PTR(-ENOMEM); | |
137 | ||
138 | spin_lock_init(&freezer->lock); | |
81dcf33c | 139 | freezer->state = CGROUP_THAWED; |
dc52ddc0 MH |
140 | return &freezer->css; |
141 | } | |
142 | ||
143 | static void freezer_destroy(struct cgroup_subsys *ss, | |
144 | struct cgroup *cgroup) | |
145 | { | |
146 | kfree(cgroup_freezer(cgroup)); | |
147 | } | |
148 | ||
957a4eea MH |
149 | /* Task is frozen or will freeze immediately when next it gets woken */ |
150 | static bool is_task_frozen_enough(struct task_struct *task) | |
151 | { | |
152 | return frozen(task) || | |
153 | (task_is_stopped_or_traced(task) && freezing(task)); | |
154 | } | |
dc52ddc0 | 155 | |
957a4eea MH |
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 | */ | |
dc52ddc0 MH |
161 | static int freezer_can_attach(struct cgroup_subsys *ss, |
162 | struct cgroup *new_cgroup, | |
be367d09 | 163 | struct task_struct *task, bool threadgroup) |
dc52ddc0 MH |
164 | { |
165 | struct freezer *freezer; | |
957a4eea | 166 | |
80a6a2cf LZ |
167 | /* |
168 | * Anything frozen can't move or be moved to/from. | |
169 | * | |
170 | * Since orig_freezer->state == FROZEN means that @task has been | |
171 | * frozen, so it's sufficient to check the latter condition. | |
172 | */ | |
957a4eea MH |
173 | |
174 | if (is_task_frozen_enough(task)) | |
175 | return -EBUSY; | |
dc52ddc0 | 176 | |
dc52ddc0 | 177 | freezer = cgroup_freezer(new_cgroup); |
81dcf33c | 178 | if (freezer->state == CGROUP_FROZEN) |
957a4eea MH |
179 | return -EBUSY; |
180 | ||
be367d09 BB |
181 | if (threadgroup) { |
182 | struct task_struct *c; | |
183 | ||
184 | rcu_read_lock(); | |
185 | list_for_each_entry_rcu(c, &task->thread_group, thread_group) { | |
186 | if (is_task_frozen_enough(c)) { | |
187 | rcu_read_unlock(); | |
188 | return -EBUSY; | |
189 | } | |
190 | } | |
191 | rcu_read_unlock(); | |
192 | } | |
193 | ||
80a6a2cf | 194 | return 0; |
dc52ddc0 MH |
195 | } |
196 | ||
197 | static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) | |
198 | { | |
199 | struct freezer *freezer; | |
200 | ||
68744676 LZ |
201 | /* |
202 | * No lock is needed, since the task isn't on tasklist yet, | |
203 | * so it can't be moved to another cgroup, which means the | |
204 | * freezer won't be removed and will be valid during this | |
205 | * function call. | |
206 | */ | |
dc52ddc0 | 207 | freezer = task_freezer(task); |
dc52ddc0 | 208 | |
3b1b3f6e LZ |
209 | /* |
210 | * The root cgroup is non-freezable, so we can skip the | |
211 | * following check. | |
212 | */ | |
213 | if (!freezer->css.cgroup->parent) | |
214 | return; | |
215 | ||
dc52ddc0 | 216 | spin_lock_irq(&freezer->lock); |
7ccb9743 LZ |
217 | BUG_ON(freezer->state == CGROUP_FROZEN); |
218 | ||
81dcf33c MH |
219 | /* Locking avoids race with FREEZING -> THAWED transitions. */ |
220 | if (freezer->state == CGROUP_FREEZING) | |
dc52ddc0 MH |
221 | freeze_task(task, true); |
222 | spin_unlock_irq(&freezer->lock); | |
223 | } | |
224 | ||
225 | /* | |
226 | * caller must hold freezer->lock | |
227 | */ | |
1aece348 MH |
228 | static void update_freezer_state(struct cgroup *cgroup, |
229 | struct freezer *freezer) | |
dc52ddc0 MH |
230 | { |
231 | struct cgroup_iter it; | |
232 | struct task_struct *task; | |
233 | unsigned int nfrozen = 0, ntotal = 0; | |
234 | ||
235 | cgroup_iter_start(cgroup, &it); | |
236 | while ((task = cgroup_iter_next(cgroup, &it))) { | |
237 | ntotal++; | |
957a4eea | 238 | if (is_task_frozen_enough(task)) |
dc52ddc0 MH |
239 | nfrozen++; |
240 | } | |
241 | ||
242 | /* | |
243 | * Transition to FROZEN when no new tasks can be added ensures | |
244 | * that we never exist in the FROZEN state while there are unfrozen | |
245 | * tasks. | |
246 | */ | |
247 | if (nfrozen == ntotal) | |
81dcf33c | 248 | freezer->state = CGROUP_FROZEN; |
1aece348 MH |
249 | else if (nfrozen > 0) |
250 | freezer->state = CGROUP_FREEZING; | |
251 | else | |
252 | freezer->state = CGROUP_THAWED; | |
dc52ddc0 MH |
253 | cgroup_iter_end(cgroup, &it); |
254 | } | |
255 | ||
256 | static int freezer_read(struct cgroup *cgroup, struct cftype *cft, | |
257 | struct seq_file *m) | |
258 | { | |
259 | struct freezer *freezer; | |
260 | enum freezer_state state; | |
261 | ||
262 | if (!cgroup_lock_live_group(cgroup)) | |
263 | return -ENODEV; | |
264 | ||
265 | freezer = cgroup_freezer(cgroup); | |
266 | spin_lock_irq(&freezer->lock); | |
267 | state = freezer->state; | |
81dcf33c | 268 | if (state == CGROUP_FREEZING) { |
dc52ddc0 MH |
269 | /* We change from FREEZING to FROZEN lazily if the cgroup was |
270 | * only partially frozen when we exitted write. */ | |
1aece348 | 271 | update_freezer_state(cgroup, freezer); |
dc52ddc0 MH |
272 | state = freezer->state; |
273 | } | |
274 | spin_unlock_irq(&freezer->lock); | |
275 | cgroup_unlock(); | |
276 | ||
277 | seq_puts(m, freezer_state_strs[state]); | |
278 | seq_putc(m, '\n'); | |
279 | return 0; | |
280 | } | |
281 | ||
282 | static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) | |
283 | { | |
284 | struct cgroup_iter it; | |
285 | struct task_struct *task; | |
286 | unsigned int num_cant_freeze_now = 0; | |
287 | ||
81dcf33c | 288 | freezer->state = CGROUP_FREEZING; |
dc52ddc0 MH |
289 | cgroup_iter_start(cgroup, &it); |
290 | while ((task = cgroup_iter_next(cgroup, &it))) { | |
291 | if (!freeze_task(task, true)) | |
292 | continue; | |
957a4eea | 293 | if (is_task_frozen_enough(task)) |
dc52ddc0 MH |
294 | continue; |
295 | if (!freezing(task) && !freezer_should_skip(task)) | |
296 | num_cant_freeze_now++; | |
297 | } | |
298 | cgroup_iter_end(cgroup, &it); | |
299 | ||
300 | return num_cant_freeze_now ? -EBUSY : 0; | |
301 | } | |
302 | ||
00c2e63c | 303 | static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
dc52ddc0 MH |
304 | { |
305 | struct cgroup_iter it; | |
306 | struct task_struct *task; | |
307 | ||
308 | cgroup_iter_start(cgroup, &it); | |
309 | while ((task = cgroup_iter_next(cgroup, &it))) { | |
00c2e63c | 310 | thaw_process(task); |
dc52ddc0 MH |
311 | } |
312 | cgroup_iter_end(cgroup, &it); | |
dc52ddc0 | 313 | |
00c2e63c | 314 | freezer->state = CGROUP_THAWED; |
dc52ddc0 MH |
315 | } |
316 | ||
317 | static int freezer_change_state(struct cgroup *cgroup, | |
318 | enum freezer_state goal_state) | |
319 | { | |
320 | struct freezer *freezer; | |
321 | int retval = 0; | |
322 | ||
323 | freezer = cgroup_freezer(cgroup); | |
51308ee5 | 324 | |
dc52ddc0 | 325 | spin_lock_irq(&freezer->lock); |
51308ee5 | 326 | |
1aece348 | 327 | update_freezer_state(cgroup, freezer); |
dc52ddc0 MH |
328 | if (goal_state == freezer->state) |
329 | goto out; | |
51308ee5 LZ |
330 | |
331 | switch (goal_state) { | |
81dcf33c | 332 | case CGROUP_THAWED: |
51308ee5 | 333 | unfreeze_cgroup(cgroup, freezer); |
dc52ddc0 | 334 | break; |
81dcf33c | 335 | case CGROUP_FROZEN: |
51308ee5 | 336 | retval = try_to_freeze_cgroup(cgroup, freezer); |
dc52ddc0 MH |
337 | break; |
338 | default: | |
51308ee5 | 339 | BUG(); |
dc52ddc0 MH |
340 | } |
341 | out: | |
342 | spin_unlock_irq(&freezer->lock); | |
343 | ||
344 | return retval; | |
345 | } | |
346 | ||
347 | static int freezer_write(struct cgroup *cgroup, | |
348 | struct cftype *cft, | |
349 | const char *buffer) | |
350 | { | |
351 | int retval; | |
352 | enum freezer_state goal_state; | |
353 | ||
81dcf33c MH |
354 | if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0) |
355 | goal_state = CGROUP_THAWED; | |
356 | else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0) | |
357 | goal_state = CGROUP_FROZEN; | |
dc52ddc0 | 358 | else |
3b1b3f6e | 359 | return -EINVAL; |
dc52ddc0 MH |
360 | |
361 | if (!cgroup_lock_live_group(cgroup)) | |
362 | return -ENODEV; | |
363 | retval = freezer_change_state(cgroup, goal_state); | |
364 | cgroup_unlock(); | |
365 | return retval; | |
366 | } | |
367 | ||
368 | static struct cftype files[] = { | |
369 | { | |
370 | .name = "state", | |
371 | .read_seq_string = freezer_read, | |
372 | .write_string = freezer_write, | |
373 | }, | |
374 | }; | |
375 | ||
376 | static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup) | |
377 | { | |
3b1b3f6e LZ |
378 | if (!cgroup->parent) |
379 | return 0; | |
dc52ddc0 MH |
380 | return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files)); |
381 | } | |
382 | ||
383 | struct cgroup_subsys freezer_subsys = { | |
384 | .name = "freezer", | |
385 | .create = freezer_create, | |
386 | .destroy = freezer_destroy, | |
387 | .populate = freezer_populate, | |
388 | .subsys_id = freezer_subsys_id, | |
389 | .can_attach = freezer_can_attach, | |
390 | .attach = NULL, | |
391 | .fork = freezer_fork, | |
392 | .exit = NULL, | |
393 | }; |