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/export.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
cgroup_freezer(struct cgroup * cgroup)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
task_freezer(struct task_struct * task)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
cgroup_freezing(struct task_struct * task)51 bool cgroup_freezing(struct task_struct *task)
52 {
53 enum freezer_state state;
54 bool ret;
55
56 rcu_read_lock();
57 state = task_freezer(task)->state;
58 ret = state == CGROUP_FREEZING || state == CGROUP_FROZEN;
59 rcu_read_unlock();
60
61 return ret;
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[] = {
69 "THAWED",
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 *
79 * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
80 * ^ ^ | |
81 * | \_______THAWED_______/ |
82 * \__________________________THAWED____________/
83 */
84
85 struct cgroup_subsys freezer_subsys;
86
87 /* Locks taken and their ordering
88 * ------------------------------
89 * cgroup_mutex (AKA cgroup_lock)
90 * freezer->lock
91 * css_set_lock
92 * task->alloc_lock (AKA task_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 * freezer_can_attach():
101 * cgroup_mutex (held by caller of can_attach)
102 *
103 * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
104 * freezer->lock
105 * sighand->siglock (if the cgroup is freezing)
106 *
107 * freezer_read():
108 * cgroup_mutex
109 * freezer->lock
110 * write_lock css_set_lock (cgroup iterator start)
111 * task->alloc_lock
112 * read_lock css_set_lock (cgroup iterator start)
113 *
114 * freezer_write() (freeze):
115 * cgroup_mutex
116 * freezer->lock
117 * write_lock css_set_lock (cgroup iterator start)
118 * task->alloc_lock
119 * read_lock css_set_lock (cgroup iterator start)
120 * sighand->siglock (fake signal delivery inside freeze_task())
121 *
122 * freezer_write() (unfreeze):
123 * cgroup_mutex
124 * freezer->lock
125 * write_lock css_set_lock (cgroup iterator start)
126 * task->alloc_lock
127 * read_lock css_set_lock (cgroup iterator start)
128 * task->alloc_lock (inside __thaw_task(), prevents race with refrigerator())
129 * sighand->siglock
130 */
freezer_create(struct cgroup * cgroup)131 static struct cgroup_subsys_state *freezer_create(struct cgroup *cgroup)
132 {
133 struct freezer *freezer;
134
135 freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
136 if (!freezer)
137 return ERR_PTR(-ENOMEM);
138
139 spin_lock_init(&freezer->lock);
140 freezer->state = CGROUP_THAWED;
141 return &freezer->css;
142 }
143
freezer_destroy(struct cgroup * cgroup)144 static void freezer_destroy(struct cgroup *cgroup)
145 {
146 struct freezer *freezer = cgroup_freezer(cgroup);
147
148 if (freezer->state != CGROUP_THAWED)
149 atomic_dec(&system_freezing_cnt);
150 kfree(freezer);
151 }
152
153 /* task is frozen or will freeze immediately when next it gets woken */
is_task_frozen_enough(struct task_struct * task)154 static bool is_task_frozen_enough(struct task_struct *task)
155 {
156 return frozen(task) ||
157 (task_is_stopped_or_traced(task) && freezing(task));
158 }
159
160 /*
161 * The call to cgroup_lock() in the freezer.state write method prevents
162 * a write to that file racing against an attach, and hence the
163 * can_attach() result will remain valid until the attach completes.
164 */
freezer_can_attach(struct cgroup * new_cgroup,struct cgroup_taskset * tset)165 static int freezer_can_attach(struct cgroup *new_cgroup,
166 struct cgroup_taskset *tset)
167 {
168 struct freezer *freezer;
169 struct task_struct *task;
170
171 /*
172 * Anything frozen can't move or be moved to/from.
173 */
174 cgroup_taskset_for_each(task, new_cgroup, tset)
175 if (cgroup_freezing(task))
176 return -EBUSY;
177
178 freezer = cgroup_freezer(new_cgroup);
179 if (freezer->state != CGROUP_THAWED)
180 return -EBUSY;
181
182 return 0;
183 }
184
freezer_fork(struct task_struct * task)185 static void freezer_fork(struct task_struct *task)
186 {
187 struct freezer *freezer;
188
189 rcu_read_lock();
190 freezer = task_freezer(task);
191
192 /*
193 * The root cgroup is non-freezable, so we can skip the
194 * following check.
195 */
196 if (!freezer->css.cgroup->parent)
197 goto out;
198
199 spin_lock_irq(&freezer->lock);
200 BUG_ON(freezer->state == CGROUP_FROZEN);
201
202 /* Locking avoids race with FREEZING -> THAWED transitions. */
203 if (freezer->state == CGROUP_FREEZING)
204 freeze_task(task);
205
206 spin_unlock_irq(&freezer->lock);
207 out:
208 rcu_read_unlock();
209 }
210
211 /*
212 * caller must hold freezer->lock
213 */
update_if_frozen(struct cgroup * cgroup,struct freezer * freezer)214 static void update_if_frozen(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 enum freezer_state old_state = freezer->state;
221
222 cgroup_iter_start(cgroup, &it);
223 while ((task = cgroup_iter_next(cgroup, &it))) {
224 ntotal++;
225 if (freezing(task) && is_task_frozen_enough(task))
226 nfrozen++;
227 }
228
229 if (old_state == CGROUP_THAWED) {
230 BUG_ON(nfrozen > 0);
231 } else if (old_state == CGROUP_FREEZING) {
232 if (nfrozen == ntotal)
233 freezer->state = CGROUP_FROZEN;
234 } else { /* old_state == CGROUP_FROZEN */
235 BUG_ON(nfrozen != ntotal);
236 }
237
238 cgroup_iter_end(cgroup, &it);
239 }
240
freezer_read(struct cgroup * cgroup,struct cftype * cft,struct seq_file * m)241 static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
242 struct seq_file *m)
243 {
244 struct freezer *freezer;
245 enum freezer_state state;
246
247 if (!cgroup_lock_live_group(cgroup))
248 return -ENODEV;
249
250 freezer = cgroup_freezer(cgroup);
251 spin_lock_irq(&freezer->lock);
252 state = freezer->state;
253 if (state == CGROUP_FREEZING) {
254 /* We change from FREEZING to FROZEN lazily if the cgroup was
255 * only partially frozen when we exitted write. */
256 update_if_frozen(cgroup, freezer);
257 state = freezer->state;
258 }
259 spin_unlock_irq(&freezer->lock);
260 cgroup_unlock();
261
262 seq_puts(m, freezer_state_strs[state]);
263 seq_putc(m, '\n');
264 return 0;
265 }
266
try_to_freeze_cgroup(struct cgroup * cgroup,struct freezer * freezer)267 static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
268 {
269 struct cgroup_iter it;
270 struct task_struct *task;
271 unsigned int num_cant_freeze_now = 0;
272
273 cgroup_iter_start(cgroup, &it);
274 while ((task = cgroup_iter_next(cgroup, &it))) {
275 if (!freeze_task(task))
276 continue;
277 if (is_task_frozen_enough(task))
278 continue;
279 if (!freezing(task) && !freezer_should_skip(task))
280 num_cant_freeze_now++;
281 }
282 cgroup_iter_end(cgroup, &it);
283
284 return num_cant_freeze_now ? -EBUSY : 0;
285 }
286
unfreeze_cgroup(struct cgroup * cgroup,struct freezer * freezer)287 static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
288 {
289 struct cgroup_iter it;
290 struct task_struct *task;
291
292 cgroup_iter_start(cgroup, &it);
293 while ((task = cgroup_iter_next(cgroup, &it)))
294 __thaw_task(task);
295 cgroup_iter_end(cgroup, &it);
296 }
297
freezer_change_state(struct cgroup * cgroup,enum freezer_state goal_state)298 static int freezer_change_state(struct cgroup *cgroup,
299 enum freezer_state goal_state)
300 {
301 struct freezer *freezer;
302 int retval = 0;
303
304 freezer = cgroup_freezer(cgroup);
305
306 spin_lock_irq(&freezer->lock);
307
308 update_if_frozen(cgroup, freezer);
309
310 switch (goal_state) {
311 case CGROUP_THAWED:
312 if (freezer->state != CGROUP_THAWED)
313 atomic_dec(&system_freezing_cnt);
314 freezer->state = CGROUP_THAWED;
315 unfreeze_cgroup(cgroup, freezer);
316 break;
317 case CGROUP_FROZEN:
318 if (freezer->state == CGROUP_THAWED)
319 atomic_inc(&system_freezing_cnt);
320 freezer->state = CGROUP_FREEZING;
321 retval = try_to_freeze_cgroup(cgroup, freezer);
322 break;
323 default:
324 BUG();
325 }
326
327 spin_unlock_irq(&freezer->lock);
328
329 return retval;
330 }
331
freezer_write(struct cgroup * cgroup,struct cftype * cft,const char * buffer)332 static int freezer_write(struct cgroup *cgroup,
333 struct cftype *cft,
334 const char *buffer)
335 {
336 int retval;
337 enum freezer_state goal_state;
338
339 if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
340 goal_state = CGROUP_THAWED;
341 else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
342 goal_state = CGROUP_FROZEN;
343 else
344 return -EINVAL;
345
346 if (!cgroup_lock_live_group(cgroup))
347 return -ENODEV;
348 retval = freezer_change_state(cgroup, goal_state);
349 cgroup_unlock();
350 return retval;
351 }
352
353 static struct cftype files[] = {
354 {
355 .name = "state",
356 .read_seq_string = freezer_read,
357 .write_string = freezer_write,
358 },
359 };
360
freezer_populate(struct cgroup_subsys * ss,struct cgroup * cgroup)361 static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup)
362 {
363 if (!cgroup->parent)
364 return 0;
365 return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
366 }
367
368 struct cgroup_subsys freezer_subsys = {
369 .name = "freezer",
370 .create = freezer_create,
371 .destroy = freezer_destroy,
372 .populate = freezer_populate,
373 .subsys_id = freezer_subsys_id,
374 .can_attach = freezer_can_attach,
375 .fork = freezer_fork,
376 };
377