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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/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 | |
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 | 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 | */ |
131 | static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss, |
132 | struct cgroup *cgroup) |
133 | { |
134 | struct freezer *freezer; |
135 | |
136 | freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL); |
137 | if (!freezer) |
138 | return ERR_PTR(-ENOMEM); |
139 | |
140 | spin_lock_init(&freezer->lock); |
141 | freezer->state = CGROUP_THAWED; |
142 | return &freezer->css; |
143 | } |
144 | |
145 | static void freezer_destroy(struct cgroup_subsys *ss, |
146 | struct cgroup *cgroup) |
147 | { |
148 | struct freezer *freezer = cgroup_freezer(cgroup); |
149 | |
150 | if (freezer->state != CGROUP_THAWED) |
151 | atomic_dec(&system_freezing_cnt); |
152 | kfree(freezer); |
153 | } |
154 | |
155 | /* task is frozen or will freeze immediately when next it gets woken */ |
156 | static bool is_task_frozen_enough(struct task_struct *task) |
157 | { |
158 | return frozen(task) || |
159 | (task_is_stopped_or_traced(task) && freezing(task)); |
160 | } |
161 | |
162 | /* |
163 | * The call to cgroup_lock() in the freezer.state write method prevents |
164 | * a write to that file racing against an attach, and hence the |
165 | * can_attach() result will remain valid until the attach completes. |
166 | */ |
167 | static int freezer_can_attach(struct cgroup_subsys *ss, |
168 | struct cgroup *new_cgroup, |
169 | struct cgroup_taskset *tset) |
170 | { |
171 | struct freezer *freezer; |
172 | struct task_struct *task; |
173 | |
174 | /* |
175 | * Anything frozen can't move or be moved to/from. |
176 | */ |
177 | cgroup_taskset_for_each(task, new_cgroup, tset) |
178 | if (cgroup_freezing(task)) |
179 | return -EBUSY; |
180 | |
181 | freezer = cgroup_freezer(new_cgroup); |
182 | if (freezer->state != CGROUP_THAWED) |
183 | return -EBUSY; |
184 | |
185 | return 0; |
186 | } |
187 | |
188 | static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) |
189 | { |
190 | struct freezer *freezer; |
191 | |
192 | /* |
193 | * No lock is needed, since the task isn't on tasklist yet, |
194 | * so it can't be moved to another cgroup, which means the |
195 | * freezer won't be removed and will be valid during this |
196 | * function call. Nevertheless, apply RCU read-side critical |
197 | * section to suppress RCU lockdep false positives. |
198 | */ |
199 | rcu_read_lock(); |
200 | freezer = task_freezer(task); |
201 | rcu_read_unlock(); |
202 | |
203 | /* |
204 | * The root cgroup is non-freezable, so we can skip the |
205 | * following check. |
206 | */ |
207 | if (!freezer->css.cgroup->parent) |
208 | return; |
209 | |
210 | spin_lock_irq(&freezer->lock); |
211 | BUG_ON(freezer->state == CGROUP_FROZEN); |
212 | |
213 | /* Locking avoids race with FREEZING -> THAWED transitions. */ |
214 | if (freezer->state == CGROUP_FREEZING) |
215 | freeze_task(task); |
216 | spin_unlock_irq(&freezer->lock); |
217 | } |
218 | |
219 | /* |
220 | * caller must hold freezer->lock |
221 | */ |
222 | static void update_if_frozen(struct cgroup *cgroup, |
223 | struct freezer *freezer) |
224 | { |
225 | struct cgroup_iter it; |
226 | struct task_struct *task; |
227 | unsigned int nfrozen = 0, ntotal = 0; |
228 | enum freezer_state old_state = freezer->state; |
229 | |
230 | cgroup_iter_start(cgroup, &it); |
231 | while ((task = cgroup_iter_next(cgroup, &it))) { |
232 | ntotal++; |
233 | if (freezing(task) && is_task_frozen_enough(task)) |
234 | nfrozen++; |
235 | } |
236 | |
237 | if (old_state == CGROUP_THAWED) { |
238 | BUG_ON(nfrozen > 0); |
239 | } else if (old_state == CGROUP_FREEZING) { |
240 | if (nfrozen == ntotal) |
241 | freezer->state = CGROUP_FROZEN; |
242 | } else { /* old_state == CGROUP_FROZEN */ |
243 | BUG_ON(nfrozen != ntotal); |
244 | } |
245 | |
246 | cgroup_iter_end(cgroup, &it); |
247 | } |
248 | |
249 | static int freezer_read(struct cgroup *cgroup, struct cftype *cft, |
250 | struct seq_file *m) |
251 | { |
252 | struct freezer *freezer; |
253 | enum freezer_state state; |
254 | |
255 | if (!cgroup_lock_live_group(cgroup)) |
256 | return -ENODEV; |
257 | |
258 | freezer = cgroup_freezer(cgroup); |
259 | spin_lock_irq(&freezer->lock); |
260 | state = freezer->state; |
261 | if (state == CGROUP_FREEZING) { |
262 | /* We change from FREEZING to FROZEN lazily if the cgroup was |
263 | * only partially frozen when we exitted write. */ |
264 | update_if_frozen(cgroup, freezer); |
265 | state = freezer->state; |
266 | } |
267 | spin_unlock_irq(&freezer->lock); |
268 | cgroup_unlock(); |
269 | |
270 | seq_puts(m, freezer_state_strs[state]); |
271 | seq_putc(m, '\n'); |
272 | return 0; |
273 | } |
274 | |
275 | static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
276 | { |
277 | struct cgroup_iter it; |
278 | struct task_struct *task; |
279 | unsigned int num_cant_freeze_now = 0; |
280 | |
281 | cgroup_iter_start(cgroup, &it); |
282 | while ((task = cgroup_iter_next(cgroup, &it))) { |
283 | if (!freeze_task(task)) |
284 | continue; |
285 | if (is_task_frozen_enough(task)) |
286 | continue; |
287 | if (!freezing(task) && !freezer_should_skip(task)) |
288 | num_cant_freeze_now++; |
289 | } |
290 | cgroup_iter_end(cgroup, &it); |
291 | |
292 | return num_cant_freeze_now ? -EBUSY : 0; |
293 | } |
294 | |
295 | static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
296 | { |
297 | struct cgroup_iter it; |
298 | struct task_struct *task; |
299 | |
300 | cgroup_iter_start(cgroup, &it); |
301 | while ((task = cgroup_iter_next(cgroup, &it))) |
302 | __thaw_task(task); |
303 | cgroup_iter_end(cgroup, &it); |
304 | } |
305 | |
306 | static int freezer_change_state(struct cgroup *cgroup, |
307 | enum freezer_state goal_state) |
308 | { |
309 | struct freezer *freezer; |
310 | int retval = 0; |
311 | |
312 | freezer = cgroup_freezer(cgroup); |
313 | |
314 | spin_lock_irq(&freezer->lock); |
315 | |
316 | update_if_frozen(cgroup, freezer); |
317 | |
318 | switch (goal_state) { |
319 | case CGROUP_THAWED: |
320 | if (freezer->state != CGROUP_THAWED) |
321 | atomic_dec(&system_freezing_cnt); |
322 | freezer->state = CGROUP_THAWED; |
323 | unfreeze_cgroup(cgroup, freezer); |
324 | break; |
325 | case CGROUP_FROZEN: |
326 | if (freezer->state == CGROUP_THAWED) |
327 | atomic_inc(&system_freezing_cnt); |
328 | freezer->state = CGROUP_FREEZING; |
329 | retval = try_to_freeze_cgroup(cgroup, freezer); |
330 | break; |
331 | default: |
332 | BUG(); |
333 | } |
334 | |
335 | spin_unlock_irq(&freezer->lock); |
336 | |
337 | return retval; |
338 | } |
339 | |
340 | static int freezer_write(struct cgroup *cgroup, |
341 | struct cftype *cft, |
342 | const char *buffer) |
343 | { |
344 | int retval; |
345 | enum freezer_state goal_state; |
346 | |
347 | if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0) |
348 | goal_state = CGROUP_THAWED; |
349 | else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0) |
350 | goal_state = CGROUP_FROZEN; |
351 | else |
352 | return -EINVAL; |
353 | |
354 | if (!cgroup_lock_live_group(cgroup)) |
355 | return -ENODEV; |
356 | retval = freezer_change_state(cgroup, goal_state); |
357 | cgroup_unlock(); |
358 | return retval; |
359 | } |
360 | |
361 | static struct cftype files[] = { |
362 | { |
363 | .name = "state", |
364 | .read_seq_string = freezer_read, |
365 | .write_string = freezer_write, |
366 | }, |
367 | }; |
368 | |
369 | static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup) |
370 | { |
371 | if (!cgroup->parent) |
372 | return 0; |
373 | return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files)); |
374 | } |
375 | |
376 | struct cgroup_subsys freezer_subsys = { |
377 | .name = "freezer", |
378 | .create = freezer_create, |
379 | .destroy = freezer_destroy, |
380 | .populate = freezer_populate, |
381 | .subsys_id = freezer_subsys_id, |
382 | .can_attach = freezer_can_attach, |
383 | .fork = freezer_fork, |
384 | }; |
385 |
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