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)
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 return 0;
181 }
182
183 static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
184 {
185 struct freezer *freezer;
186
187 /*
188 * No lock is needed, since the task isn't on tasklist yet,
189 * so it can't be moved to another cgroup, which means the
190 * freezer won't be removed and will be valid during this
191 * function call.
192 */
193 freezer = task_freezer(task);
194
195 /*
196 * The root cgroup is non-freezable, so we can skip the
197 * following check.
198 */
199 if (!freezer->css.cgroup->parent)
200 return;
201
202 spin_lock_irq(&freezer->lock);
203 BUG_ON(freezer->state == CGROUP_FROZEN);
204
205 /* Locking avoids race with FREEZING -> THAWED transitions. */
206 if (freezer->state == CGROUP_FREEZING)
207 freeze_task(task, true);
208 spin_unlock_irq(&freezer->lock);
209 }
210
211 /*
212 * caller must hold freezer->lock
213 */
214 static void update_freezer_state(struct cgroup *cgroup,
215 struct freezer *freezer)
216 {
217 struct cgroup_iter it;
218 struct task_struct *task;
219 unsigned int nfrozen = 0, ntotal = 0;
220
221 cgroup_iter_start(cgroup, &it);
222 while ((task = cgroup_iter_next(cgroup, &it))) {
223 ntotal++;
224 if (is_task_frozen_enough(task))
225 nfrozen++;
226 }
227
228 /*
229 * Transition to FROZEN when no new tasks can be added ensures
230 * that we never exist in the FROZEN state while there are unfrozen
231 * tasks.
232 */
233 if (nfrozen == ntotal)
234 freezer->state = CGROUP_FROZEN;
235 else if (nfrozen > 0)
236 freezer->state = CGROUP_FREEZING;
237 else
238 freezer->state = CGROUP_THAWED;
239 cgroup_iter_end(cgroup, &it);
240 }
241
242 static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
243 struct seq_file *m)
244 {
245 struct freezer *freezer;
246 enum freezer_state state;
247
248 if (!cgroup_lock_live_group(cgroup))
249 return -ENODEV;
250
251 freezer = cgroup_freezer(cgroup);
252 spin_lock_irq(&freezer->lock);
253 state = freezer->state;
254 if (state == CGROUP_FREEZING) {
255 /* We change from FREEZING to FROZEN lazily if the cgroup was
256 * only partially frozen when we exitted write. */
257 update_freezer_state(cgroup, freezer);
258 state = freezer->state;
259 }
260 spin_unlock_irq(&freezer->lock);
261 cgroup_unlock();
262
263 seq_puts(m, freezer_state_strs[state]);
264 seq_putc(m, '\n');
265 return 0;
266 }
267
268 static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
269 {
270 struct cgroup_iter it;
271 struct task_struct *task;
272 unsigned int num_cant_freeze_now = 0;
273
274 freezer->state = CGROUP_FREEZING;
275 cgroup_iter_start(cgroup, &it);
276 while ((task = cgroup_iter_next(cgroup, &it))) {
277 if (!freeze_task(task, true))
278 continue;
279 if (is_task_frozen_enough(task))
280 continue;
281 if (!freezing(task) && !freezer_should_skip(task))
282 num_cant_freeze_now++;
283 }
284 cgroup_iter_end(cgroup, &it);
285
286 return num_cant_freeze_now ? -EBUSY : 0;
287 }
288
289 static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
290 {
291 struct cgroup_iter it;
292 struct task_struct *task;
293
294 cgroup_iter_start(cgroup, &it);
295 while ((task = cgroup_iter_next(cgroup, &it))) {
296 thaw_process(task);
297 }
298 cgroup_iter_end(cgroup, &it);
299
300 freezer->state = CGROUP_THAWED;
301 }
302
303 static int freezer_change_state(struct cgroup *cgroup,
304 enum freezer_state goal_state)
305 {
306 struct freezer *freezer;
307 int retval = 0;
308
309 freezer = cgroup_freezer(cgroup);
310
311 spin_lock_irq(&freezer->lock);
312
313 update_freezer_state(cgroup, freezer);
314 if (goal_state == freezer->state)
315 goto out;
316
317 switch (goal_state) {
318 case CGROUP_THAWED:
319 unfreeze_cgroup(cgroup, freezer);
320 break;
321 case CGROUP_FROZEN:
322 retval = try_to_freeze_cgroup(cgroup, freezer);
323 break;
324 default:
325 BUG();
326 }
327 out:
328 spin_unlock_irq(&freezer->lock);
329
330 return retval;
331 }
332
333 static int freezer_write(struct cgroup *cgroup,
334 struct cftype *cft,
335 const char *buffer)
336 {
337 int retval;
338 enum freezer_state goal_state;
339
340 if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
341 goal_state = CGROUP_THAWED;
342 else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
343 goal_state = CGROUP_FROZEN;
344 else
345 return -EINVAL;
346
347 if (!cgroup_lock_live_group(cgroup))
348 return -ENODEV;
349 retval = freezer_change_state(cgroup, goal_state);
350 cgroup_unlock();
351 return retval;
352 }
353
354 static struct cftype files[] = {
355 {
356 .name = "state",
357 .read_seq_string = freezer_read,
358 .write_string = freezer_write,
359 },
360 };
361
362 static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup)
363 {
364 if (!cgroup->parent)
365 return 0;
366 return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
367 }
368
369 struct cgroup_subsys freezer_subsys = {
370 .name = "freezer",
371 .create = freezer_create,
372 .destroy = freezer_destroy,
373 .populate = freezer_populate,
374 .subsys_id = freezer_subsys_id,
375 .can_attach = freezer_can_attach,
376 .attach = NULL,
377 .fork = freezer_fork,
378 .exit = NULL,
379 };
380
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