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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 | { | |
148 | kfree(cgroup_freezer(cgroup)); | |
149 | } | |
150 | ||
957a4eea MH |
151 | /* |
152 | * The call to cgroup_lock() in the freezer.state write method prevents | |
153 | * a write to that file racing against an attach, and hence the | |
154 | * can_attach() result will remain valid until the attach completes. | |
155 | */ | |
dc52ddc0 MH |
156 | static int freezer_can_attach(struct cgroup_subsys *ss, |
157 | struct cgroup *new_cgroup, | |
f780bdb7 | 158 | struct task_struct *task) |
dc52ddc0 MH |
159 | { |
160 | struct freezer *freezer; | |
957a4eea | 161 | |
80a6a2cf LZ |
162 | /* |
163 | * Anything frozen can't move or be moved to/from. | |
80a6a2cf | 164 | */ |
957a4eea | 165 | |
0bdba580 TB |
166 | freezer = cgroup_freezer(new_cgroup); |
167 | if (freezer->state != CGROUP_THAWED) | |
957a4eea | 168 | return -EBUSY; |
dc52ddc0 | 169 | |
f780bdb7 BB |
170 | return 0; |
171 | } | |
172 | ||
173 | static int freezer_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk) | |
174 | { | |
22b4e111 | 175 | return cgroup_freezing(tsk) ? -EBUSY : 0; |
dc52ddc0 MH |
176 | } |
177 | ||
178 | static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) | |
179 | { | |
180 | struct freezer *freezer; | |
181 | ||
68744676 LZ |
182 | /* |
183 | * No lock is needed, since the task isn't on tasklist yet, | |
184 | * so it can't be moved to another cgroup, which means the | |
185 | * freezer won't be removed and will be valid during this | |
8b46f880 PM |
186 | * function call. Nevertheless, apply RCU read-side critical |
187 | * section to suppress RCU lockdep false positives. | |
68744676 | 188 | */ |
8b46f880 | 189 | rcu_read_lock(); |
dc52ddc0 | 190 | freezer = task_freezer(task); |
8b46f880 | 191 | rcu_read_unlock(); |
dc52ddc0 | 192 | |
3b1b3f6e LZ |
193 | /* |
194 | * The root cgroup is non-freezable, so we can skip the | |
195 | * following check. | |
196 | */ | |
197 | if (!freezer->css.cgroup->parent) | |
198 | return; | |
199 | ||
dc52ddc0 | 200 | spin_lock_irq(&freezer->lock); |
7ccb9743 LZ |
201 | BUG_ON(freezer->state == CGROUP_FROZEN); |
202 | ||
81dcf33c MH |
203 | /* Locking avoids race with FREEZING -> THAWED transitions. */ |
204 | if (freezer->state == CGROUP_FREEZING) | |
dc52ddc0 MH |
205 | freeze_task(task, true); |
206 | spin_unlock_irq(&freezer->lock); | |
207 | } | |
208 | ||
209 | /* | |
210 | * caller must hold freezer->lock | |
211 | */ | |
2d3cbf8b | 212 | static void update_if_frozen(struct cgroup *cgroup, |
1aece348 | 213 | struct freezer *freezer) |
dc52ddc0 MH |
214 | { |
215 | struct cgroup_iter it; | |
216 | struct task_struct *task; | |
217 | unsigned int nfrozen = 0, ntotal = 0; | |
2d3cbf8b | 218 | enum freezer_state old_state = freezer->state; |
dc52ddc0 MH |
219 | |
220 | cgroup_iter_start(cgroup, &it); | |
221 | while ((task = cgroup_iter_next(cgroup, &it))) { | |
222 | ntotal++; | |
6907483b | 223 | if (freezing(task) && frozen(task)) |
dc52ddc0 MH |
224 | nfrozen++; |
225 | } | |
226 | ||
2d3cbf8b TB |
227 | if (old_state == CGROUP_THAWED) { |
228 | BUG_ON(nfrozen > 0); | |
229 | } else if (old_state == CGROUP_FREEZING) { | |
230 | if (nfrozen == ntotal) | |
231 | freezer->state = CGROUP_FROZEN; | |
232 | } else { /* old_state == CGROUP_FROZEN */ | |
233 | BUG_ON(nfrozen != ntotal); | |
234 | } | |
235 | ||
dc52ddc0 MH |
236 | cgroup_iter_end(cgroup, &it); |
237 | } | |
238 | ||
239 | static int freezer_read(struct cgroup *cgroup, struct cftype *cft, | |
240 | struct seq_file *m) | |
241 | { | |
242 | struct freezer *freezer; | |
243 | enum freezer_state state; | |
244 | ||
245 | if (!cgroup_lock_live_group(cgroup)) | |
246 | return -ENODEV; | |
247 | ||
248 | freezer = cgroup_freezer(cgroup); | |
249 | spin_lock_irq(&freezer->lock); | |
250 | state = freezer->state; | |
81dcf33c | 251 | if (state == CGROUP_FREEZING) { |
dc52ddc0 MH |
252 | /* We change from FREEZING to FROZEN lazily if the cgroup was |
253 | * only partially frozen when we exitted write. */ | |
2d3cbf8b | 254 | update_if_frozen(cgroup, freezer); |
dc52ddc0 MH |
255 | state = freezer->state; |
256 | } | |
257 | spin_unlock_irq(&freezer->lock); | |
258 | cgroup_unlock(); | |
259 | ||
260 | seq_puts(m, freezer_state_strs[state]); | |
261 | seq_putc(m, '\n'); | |
262 | return 0; | |
263 | } | |
264 | ||
265 | static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) | |
266 | { | |
267 | struct cgroup_iter it; | |
268 | struct task_struct *task; | |
269 | unsigned int num_cant_freeze_now = 0; | |
270 | ||
dc52ddc0 MH |
271 | cgroup_iter_start(cgroup, &it); |
272 | while ((task = cgroup_iter_next(cgroup, &it))) { | |
273 | if (!freeze_task(task, true)) | |
274 | continue; | |
2d3cbf8b | 275 | if (frozen(task)) |
dc52ddc0 MH |
276 | continue; |
277 | if (!freezing(task) && !freezer_should_skip(task)) | |
278 | num_cant_freeze_now++; | |
279 | } | |
280 | cgroup_iter_end(cgroup, &it); | |
281 | ||
282 | return num_cant_freeze_now ? -EBUSY : 0; | |
283 | } | |
284 | ||
00c2e63c | 285 | static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
dc52ddc0 MH |
286 | { |
287 | struct cgroup_iter it; | |
288 | struct task_struct *task; | |
289 | ||
290 | cgroup_iter_start(cgroup, &it); | |
a5be2d0d TH |
291 | while ((task = cgroup_iter_next(cgroup, &it))) |
292 | __thaw_task(task); | |
dc52ddc0 | 293 | cgroup_iter_end(cgroup, &it); |
dc52ddc0 MH |
294 | } |
295 | ||
296 | static int freezer_change_state(struct cgroup *cgroup, | |
297 | enum freezer_state goal_state) | |
298 | { | |
299 | struct freezer *freezer; | |
300 | int retval = 0; | |
301 | ||
302 | freezer = cgroup_freezer(cgroup); | |
51308ee5 | 303 | |
dc52ddc0 | 304 | spin_lock_irq(&freezer->lock); |
51308ee5 | 305 | |
2d3cbf8b | 306 | update_if_frozen(cgroup, freezer); |
51308ee5 LZ |
307 | |
308 | switch (goal_state) { | |
81dcf33c | 309 | case CGROUP_THAWED: |
22b4e111 | 310 | freezer->state = CGROUP_THAWED; |
51308ee5 | 311 | unfreeze_cgroup(cgroup, freezer); |
dc52ddc0 | 312 | break; |
81dcf33c | 313 | case CGROUP_FROZEN: |
22b4e111 | 314 | freezer->state = CGROUP_FREEZING; |
51308ee5 | 315 | retval = try_to_freeze_cgroup(cgroup, freezer); |
dc52ddc0 MH |
316 | break; |
317 | default: | |
51308ee5 | 318 | BUG(); |
dc52ddc0 | 319 | } |
22b4e111 | 320 | |
dc52ddc0 MH |
321 | spin_unlock_irq(&freezer->lock); |
322 | ||
323 | return retval; | |
324 | } | |
325 | ||
326 | static int freezer_write(struct cgroup *cgroup, | |
327 | struct cftype *cft, | |
328 | const char *buffer) | |
329 | { | |
330 | int retval; | |
331 | enum freezer_state goal_state; | |
332 | ||
81dcf33c MH |
333 | if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0) |
334 | goal_state = CGROUP_THAWED; | |
335 | else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0) | |
336 | goal_state = CGROUP_FROZEN; | |
dc52ddc0 | 337 | else |
3b1b3f6e | 338 | return -EINVAL; |
dc52ddc0 MH |
339 | |
340 | if (!cgroup_lock_live_group(cgroup)) | |
341 | return -ENODEV; | |
342 | retval = freezer_change_state(cgroup, goal_state); | |
343 | cgroup_unlock(); | |
344 | return retval; | |
345 | } | |
346 | ||
347 | static struct cftype files[] = { | |
348 | { | |
349 | .name = "state", | |
350 | .read_seq_string = freezer_read, | |
351 | .write_string = freezer_write, | |
352 | }, | |
353 | }; | |
354 | ||
355 | static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup) | |
356 | { | |
3b1b3f6e LZ |
357 | if (!cgroup->parent) |
358 | return 0; | |
dc52ddc0 MH |
359 | return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files)); |
360 | } | |
361 | ||
362 | struct cgroup_subsys freezer_subsys = { | |
363 | .name = "freezer", | |
364 | .create = freezer_create, | |
365 | .destroy = freezer_destroy, | |
366 | .populate = freezer_populate, | |
367 | .subsys_id = freezer_subsys_id, | |
368 | .can_attach = freezer_can_attach, | |
f780bdb7 BB |
369 | .can_attach_task = freezer_can_attach_task, |
370 | .pre_attach = NULL, | |
371 | .attach_task = NULL, | |
dc52ddc0 MH |
372 | .attach = NULL, |
373 | .fork = freezer_fork, | |
374 | .exit = NULL, | |
375 | }; |