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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 | ||
9984de1a | 17 | #include <linux/export.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 | ||
22b4e111 | 51 | bool cgroup_freezing(struct task_struct *task) |
dc52ddc0 | 52 | { |
22b4e111 TH |
53 | enum freezer_state state; |
54 | bool ret; | |
dc52ddc0 | 55 | |
22b4e111 TH |
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; | |
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 | * ------------------------------ | |
dc52ddc0 | 89 | * cgroup_mutex (AKA cgroup_lock) |
dc52ddc0 | 90 | * freezer->lock |
8f77578c MH |
91 | * css_set_lock |
92 | * task->alloc_lock (AKA task_lock) | |
dc52ddc0 MH |
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 | * | |
8f77578c MH |
100 | * freezer_can_attach(): |
101 | * cgroup_mutex (held by caller of can_attach) | |
dc52ddc0 | 102 | * |
dc52ddc0 | 103 | * freezer_fork() (preserving fork() performance means can't take cgroup_mutex): |
dc52ddc0 MH |
104 | * freezer->lock |
105 | * sighand->siglock (if the cgroup is freezing) | |
106 | * | |
107 | * freezer_read(): | |
108 | * cgroup_mutex | |
109 | * freezer->lock | |
8f77578c MH |
110 | * write_lock css_set_lock (cgroup iterator start) |
111 | * task->alloc_lock | |
dc52ddc0 MH |
112 | * read_lock css_set_lock (cgroup iterator start) |
113 | * | |
114 | * freezer_write() (freeze): | |
115 | * cgroup_mutex | |
116 | * freezer->lock | |
8f77578c MH |
117 | * write_lock css_set_lock (cgroup iterator start) |
118 | * task->alloc_lock | |
dc52ddc0 | 119 | * read_lock css_set_lock (cgroup iterator start) |
8f77578c | 120 | * sighand->siglock (fake signal delivery inside freeze_task()) |
dc52ddc0 MH |
121 | * |
122 | * freezer_write() (unfreeze): | |
123 | * cgroup_mutex | |
124 | * freezer->lock | |
8f77578c MH |
125 | * write_lock css_set_lock (cgroup iterator start) |
126 | * task->alloc_lock | |
dc52ddc0 | 127 | * read_lock css_set_lock (cgroup iterator start) |
a5be2d0d | 128 | * task->alloc_lock (inside __thaw_task(), prevents race with refrigerator()) |
dc52ddc0 MH |
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); | |
81dcf33c | 141 | freezer->state = CGROUP_THAWED; |
dc52ddc0 MH |
142 | return &freezer->css; |
143 | } | |
144 | ||
145 | static void freezer_destroy(struct cgroup_subsys *ss, | |
146 | struct cgroup *cgroup) | |
147 | { | |
a3201227 TH |
148 | struct freezer *freezer = cgroup_freezer(cgroup); |
149 | ||
150 | if (freezer->state != CGROUP_THAWED) | |
151 | atomic_dec(&system_freezing_cnt); | |
152 | kfree(freezer); | |
dc52ddc0 MH |
153 | } |
154 | ||
957a4eea MH |
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 | */ | |
dc52ddc0 MH |
160 | static int freezer_can_attach(struct cgroup_subsys *ss, |
161 | struct cgroup *new_cgroup, | |
f780bdb7 | 162 | struct task_struct *task) |
dc52ddc0 MH |
163 | { |
164 | struct freezer *freezer; | |
957a4eea | 165 | |
80a6a2cf LZ |
166 | /* |
167 | * Anything frozen can't move or be moved to/from. | |
80a6a2cf | 168 | */ |
957a4eea | 169 | |
0bdba580 TB |
170 | freezer = cgroup_freezer(new_cgroup); |
171 | if (freezer->state != CGROUP_THAWED) | |
957a4eea | 172 | return -EBUSY; |
dc52ddc0 | 173 | |
f780bdb7 BB |
174 | return 0; |
175 | } | |
176 | ||
177 | static int freezer_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk) | |
178 | { | |
22b4e111 | 179 | return cgroup_freezing(tsk) ? -EBUSY : 0; |
dc52ddc0 MH |
180 | } |
181 | ||
182 | static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) | |
183 | { | |
184 | struct freezer *freezer; | |
185 | ||
68744676 LZ |
186 | /* |
187 | * No lock is needed, since the task isn't on tasklist yet, | |
188 | * so it can't be moved to another cgroup, which means the | |
189 | * freezer won't be removed and will be valid during this | |
8b46f880 PM |
190 | * function call. Nevertheless, apply RCU read-side critical |
191 | * section to suppress RCU lockdep false positives. | |
68744676 | 192 | */ |
8b46f880 | 193 | rcu_read_lock(); |
dc52ddc0 | 194 | freezer = task_freezer(task); |
8b46f880 | 195 | rcu_read_unlock(); |
dc52ddc0 | 196 | |
3b1b3f6e LZ |
197 | /* |
198 | * The root cgroup is non-freezable, so we can skip the | |
199 | * following check. | |
200 | */ | |
201 | if (!freezer->css.cgroup->parent) | |
202 | return; | |
203 | ||
dc52ddc0 | 204 | spin_lock_irq(&freezer->lock); |
7ccb9743 LZ |
205 | BUG_ON(freezer->state == CGROUP_FROZEN); |
206 | ||
81dcf33c MH |
207 | /* Locking avoids race with FREEZING -> THAWED transitions. */ |
208 | if (freezer->state == CGROUP_FREEZING) | |
dc52ddc0 MH |
209 | freeze_task(task, true); |
210 | spin_unlock_irq(&freezer->lock); | |
211 | } | |
212 | ||
213 | /* | |
214 | * caller must hold freezer->lock | |
215 | */ | |
2d3cbf8b | 216 | static void update_if_frozen(struct cgroup *cgroup, |
1aece348 | 217 | struct freezer *freezer) |
dc52ddc0 MH |
218 | { |
219 | struct cgroup_iter it; | |
220 | struct task_struct *task; | |
221 | unsigned int nfrozen = 0, ntotal = 0; | |
2d3cbf8b | 222 | enum freezer_state old_state = freezer->state; |
dc52ddc0 MH |
223 | |
224 | cgroup_iter_start(cgroup, &it); | |
225 | while ((task = cgroup_iter_next(cgroup, &it))) { | |
226 | ntotal++; | |
6907483b | 227 | if (freezing(task) && frozen(task)) |
dc52ddc0 MH |
228 | nfrozen++; |
229 | } | |
230 | ||
2d3cbf8b TB |
231 | if (old_state == CGROUP_THAWED) { |
232 | BUG_ON(nfrozen > 0); | |
233 | } else if (old_state == CGROUP_FREEZING) { | |
234 | if (nfrozen == ntotal) | |
235 | freezer->state = CGROUP_FROZEN; | |
236 | } else { /* old_state == CGROUP_FROZEN */ | |
237 | BUG_ON(nfrozen != ntotal); | |
238 | } | |
239 | ||
dc52ddc0 MH |
240 | cgroup_iter_end(cgroup, &it); |
241 | } | |
242 | ||
243 | static int freezer_read(struct cgroup *cgroup, struct cftype *cft, | |
244 | struct seq_file *m) | |
245 | { | |
246 | struct freezer *freezer; | |
247 | enum freezer_state state; | |
248 | ||
249 | if (!cgroup_lock_live_group(cgroup)) | |
250 | return -ENODEV; | |
251 | ||
252 | freezer = cgroup_freezer(cgroup); | |
253 | spin_lock_irq(&freezer->lock); | |
254 | state = freezer->state; | |
81dcf33c | 255 | if (state == CGROUP_FREEZING) { |
dc52ddc0 MH |
256 | /* We change from FREEZING to FROZEN lazily if the cgroup was |
257 | * only partially frozen when we exitted write. */ | |
2d3cbf8b | 258 | update_if_frozen(cgroup, freezer); |
dc52ddc0 MH |
259 | state = freezer->state; |
260 | } | |
261 | spin_unlock_irq(&freezer->lock); | |
262 | cgroup_unlock(); | |
263 | ||
264 | seq_puts(m, freezer_state_strs[state]); | |
265 | seq_putc(m, '\n'); | |
266 | return 0; | |
267 | } | |
268 | ||
269 | static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) | |
270 | { | |
271 | struct cgroup_iter it; | |
272 | struct task_struct *task; | |
273 | unsigned int num_cant_freeze_now = 0; | |
274 | ||
dc52ddc0 MH |
275 | cgroup_iter_start(cgroup, &it); |
276 | while ((task = cgroup_iter_next(cgroup, &it))) { | |
277 | if (!freeze_task(task, true)) | |
278 | continue; | |
2d3cbf8b | 279 | if (frozen(task)) |
dc52ddc0 MH |
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 | ||
00c2e63c | 289 | static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
dc52ddc0 MH |
290 | { |
291 | struct cgroup_iter it; | |
292 | struct task_struct *task; | |
293 | ||
294 | cgroup_iter_start(cgroup, &it); | |
a5be2d0d TH |
295 | while ((task = cgroup_iter_next(cgroup, &it))) |
296 | __thaw_task(task); | |
dc52ddc0 | 297 | cgroup_iter_end(cgroup, &it); |
dc52ddc0 MH |
298 | } |
299 | ||
300 | static int freezer_change_state(struct cgroup *cgroup, | |
301 | enum freezer_state goal_state) | |
302 | { | |
303 | struct freezer *freezer; | |
304 | int retval = 0; | |
305 | ||
306 | freezer = cgroup_freezer(cgroup); | |
51308ee5 | 307 | |
dc52ddc0 | 308 | spin_lock_irq(&freezer->lock); |
51308ee5 | 309 | |
2d3cbf8b | 310 | update_if_frozen(cgroup, freezer); |
51308ee5 LZ |
311 | |
312 | switch (goal_state) { | |
81dcf33c | 313 | case CGROUP_THAWED: |
a3201227 TH |
314 | if (freezer->state != CGROUP_THAWED) |
315 | atomic_dec(&system_freezing_cnt); | |
22b4e111 | 316 | freezer->state = CGROUP_THAWED; |
51308ee5 | 317 | unfreeze_cgroup(cgroup, freezer); |
dc52ddc0 | 318 | break; |
81dcf33c | 319 | case CGROUP_FROZEN: |
a3201227 TH |
320 | if (freezer->state == CGROUP_THAWED) |
321 | atomic_inc(&system_freezing_cnt); | |
22b4e111 | 322 | freezer->state = CGROUP_FREEZING; |
51308ee5 | 323 | retval = try_to_freeze_cgroup(cgroup, freezer); |
dc52ddc0 MH |
324 | break; |
325 | default: | |
51308ee5 | 326 | BUG(); |
dc52ddc0 | 327 | } |
22b4e111 | 328 | |
dc52ddc0 MH |
329 | spin_unlock_irq(&freezer->lock); |
330 | ||
331 | return retval; | |
332 | } | |
333 | ||
334 | static int freezer_write(struct cgroup *cgroup, | |
335 | struct cftype *cft, | |
336 | const char *buffer) | |
337 | { | |
338 | int retval; | |
339 | enum freezer_state goal_state; | |
340 | ||
81dcf33c MH |
341 | if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0) |
342 | goal_state = CGROUP_THAWED; | |
343 | else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0) | |
344 | goal_state = CGROUP_FROZEN; | |
dc52ddc0 | 345 | else |
3b1b3f6e | 346 | return -EINVAL; |
dc52ddc0 MH |
347 | |
348 | if (!cgroup_lock_live_group(cgroup)) | |
349 | return -ENODEV; | |
350 | retval = freezer_change_state(cgroup, goal_state); | |
351 | cgroup_unlock(); | |
352 | return retval; | |
353 | } | |
354 | ||
355 | static struct cftype files[] = { | |
356 | { | |
357 | .name = "state", | |
358 | .read_seq_string = freezer_read, | |
359 | .write_string = freezer_write, | |
360 | }, | |
361 | }; | |
362 | ||
363 | static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup) | |
364 | { | |
3b1b3f6e LZ |
365 | if (!cgroup->parent) |
366 | return 0; | |
dc52ddc0 MH |
367 | return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files)); |
368 | } | |
369 | ||
370 | struct cgroup_subsys freezer_subsys = { | |
371 | .name = "freezer", | |
372 | .create = freezer_create, | |
373 | .destroy = freezer_destroy, | |
374 | .populate = freezer_populate, | |
375 | .subsys_id = freezer_subsys_id, | |
376 | .can_attach = freezer_can_attach, | |
f780bdb7 BB |
377 | .can_attach_task = freezer_can_attach_task, |
378 | .pre_attach = NULL, | |
379 | .attach_task = NULL, | |
dc52ddc0 MH |
380 | .attach = NULL, |
381 | .fork = freezer_fork, | |
382 | .exit = NULL, | |
383 | }; |