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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 | */ | |
761b3ef5 | 131 | static struct cgroup_subsys_state *freezer_create(struct cgroup *cgroup) |
dc52ddc0 MH |
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); | |
81dcf33c | 140 | freezer->state = CGROUP_THAWED; |
dc52ddc0 MH |
141 | return &freezer->css; |
142 | } | |
143 | ||
761b3ef5 | 144 | static void freezer_destroy(struct cgroup *cgroup) |
dc52ddc0 | 145 | { |
a3201227 TH |
146 | struct freezer *freezer = cgroup_freezer(cgroup); |
147 | ||
148 | if (freezer->state != CGROUP_THAWED) | |
149 | atomic_dec(&system_freezing_cnt); | |
150 | kfree(freezer); | |
dc52ddc0 MH |
151 | } |
152 | ||
957a4eea MH |
153 | /* |
154 | * The call to cgroup_lock() in the freezer.state write method prevents | |
8755ade6 TH |
155 | * a write to that file racing against an attach, and hence we don't need |
156 | * to worry about racing against migration. | |
957a4eea | 157 | */ |
8755ade6 | 158 | static void freezer_attach(struct cgroup *new_cgrp, struct cgroup_taskset *tset) |
dc52ddc0 | 159 | { |
8755ade6 | 160 | struct freezer *freezer = cgroup_freezer(new_cgrp); |
bb9d97b6 | 161 | struct task_struct *task; |
957a4eea | 162 | |
8755ade6 TH |
163 | spin_lock_irq(&freezer->lock); |
164 | ||
80a6a2cf | 165 | /* |
8755ade6 TH |
166 | * Make the new tasks conform to the current state of @new_cgrp. |
167 | * For simplicity, when migrating any task to a FROZEN cgroup, we | |
168 | * revert it to FREEZING and let update_if_frozen() determine the | |
169 | * correct state later. | |
170 | * | |
171 | * Tasks in @tset are on @new_cgrp but may not conform to its | |
172 | * current state before executing the following - !frozen tasks may | |
173 | * be visible in a FROZEN cgroup and frozen tasks in a THAWED one. | |
174 | * This means that, to determine whether to freeze, one should test | |
175 | * whether the state equals THAWED. | |
80a6a2cf | 176 | */ |
8755ade6 TH |
177 | cgroup_taskset_for_each(task, new_cgrp, tset) { |
178 | if (freezer->state == CGROUP_THAWED) { | |
179 | __thaw_task(task); | |
180 | } else { | |
181 | freeze_task(task); | |
182 | freezer->state = CGROUP_FREEZING; | |
183 | } | |
184 | } | |
dc52ddc0 | 185 | |
8755ade6 | 186 | spin_unlock_irq(&freezer->lock); |
f780bdb7 BB |
187 | } |
188 | ||
761b3ef5 | 189 | static void freezer_fork(struct task_struct *task) |
dc52ddc0 MH |
190 | { |
191 | struct freezer *freezer; | |
192 | ||
8b46f880 | 193 | rcu_read_lock(); |
dc52ddc0 | 194 | freezer = task_freezer(task); |
dc52ddc0 | 195 | |
3b1b3f6e LZ |
196 | /* |
197 | * The root cgroup is non-freezable, so we can skip the | |
198 | * following check. | |
199 | */ | |
200 | if (!freezer->css.cgroup->parent) | |
5edee61e | 201 | goto out; |
3b1b3f6e | 202 | |
dc52ddc0 | 203 | spin_lock_irq(&freezer->lock); |
8755ade6 TH |
204 | /* |
205 | * @task might have been just migrated into a FROZEN cgroup. Test | |
206 | * equality with THAWED. Read the comment in freezer_attach(). | |
207 | */ | |
208 | if (freezer->state != CGROUP_THAWED) | |
839e3407 | 209 | freeze_task(task); |
dc52ddc0 | 210 | spin_unlock_irq(&freezer->lock); |
5edee61e TH |
211 | out: |
212 | rcu_read_unlock(); | |
dc52ddc0 MH |
213 | } |
214 | ||
215 | /* | |
216 | * caller must hold freezer->lock | |
217 | */ | |
2d3cbf8b | 218 | static void update_if_frozen(struct cgroup *cgroup, |
1aece348 | 219 | struct freezer *freezer) |
dc52ddc0 MH |
220 | { |
221 | struct cgroup_iter it; | |
222 | struct task_struct *task; | |
223 | unsigned int nfrozen = 0, ntotal = 0; | |
2d3cbf8b | 224 | enum freezer_state old_state = freezer->state; |
dc52ddc0 MH |
225 | |
226 | cgroup_iter_start(cgroup, &it); | |
227 | while ((task = cgroup_iter_next(cgroup, &it))) { | |
3c426d5e TH |
228 | if (freezing(task)) { |
229 | ntotal++; | |
230 | /* | |
231 | * freezer_should_skip() indicates that the task | |
232 | * should be skipped when determining freezing | |
233 | * completion. Consider it frozen in addition to | |
234 | * the usual frozen condition. | |
235 | */ | |
236 | if (frozen(task) || task_is_stopped_or_traced(task) || | |
237 | freezer_should_skip(task)) | |
238 | nfrozen++; | |
239 | } | |
dc52ddc0 MH |
240 | } |
241 | ||
2d3cbf8b TB |
242 | if (old_state == CGROUP_THAWED) { |
243 | BUG_ON(nfrozen > 0); | |
244 | } else if (old_state == CGROUP_FREEZING) { | |
245 | if (nfrozen == ntotal) | |
246 | freezer->state = CGROUP_FROZEN; | |
247 | } else { /* old_state == CGROUP_FROZEN */ | |
248 | BUG_ON(nfrozen != ntotal); | |
249 | } | |
250 | ||
dc52ddc0 MH |
251 | cgroup_iter_end(cgroup, &it); |
252 | } | |
253 | ||
254 | static int freezer_read(struct cgroup *cgroup, struct cftype *cft, | |
255 | struct seq_file *m) | |
256 | { | |
257 | struct freezer *freezer; | |
258 | enum freezer_state state; | |
259 | ||
260 | if (!cgroup_lock_live_group(cgroup)) | |
261 | return -ENODEV; | |
262 | ||
263 | freezer = cgroup_freezer(cgroup); | |
264 | spin_lock_irq(&freezer->lock); | |
265 | state = freezer->state; | |
81dcf33c | 266 | if (state == CGROUP_FREEZING) { |
dc52ddc0 MH |
267 | /* We change from FREEZING to FROZEN lazily if the cgroup was |
268 | * only partially frozen when we exitted write. */ | |
2d3cbf8b | 269 | update_if_frozen(cgroup, freezer); |
dc52ddc0 MH |
270 | state = freezer->state; |
271 | } | |
272 | spin_unlock_irq(&freezer->lock); | |
273 | cgroup_unlock(); | |
274 | ||
275 | seq_puts(m, freezer_state_strs[state]); | |
276 | seq_putc(m, '\n'); | |
277 | return 0; | |
278 | } | |
279 | ||
51f246ed | 280 | static void freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
dc52ddc0 MH |
281 | { |
282 | struct cgroup_iter it; | |
283 | struct task_struct *task; | |
dc52ddc0 | 284 | |
dc52ddc0 | 285 | cgroup_iter_start(cgroup, &it); |
51f246ed TH |
286 | while ((task = cgroup_iter_next(cgroup, &it))) |
287 | freeze_task(task); | |
dc52ddc0 | 288 | cgroup_iter_end(cgroup, &it); |
dc52ddc0 MH |
289 | } |
290 | ||
00c2e63c | 291 | static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
dc52ddc0 MH |
292 | { |
293 | struct cgroup_iter it; | |
294 | struct task_struct *task; | |
295 | ||
296 | cgroup_iter_start(cgroup, &it); | |
a5be2d0d TH |
297 | while ((task = cgroup_iter_next(cgroup, &it))) |
298 | __thaw_task(task); | |
dc52ddc0 | 299 | cgroup_iter_end(cgroup, &it); |
dc52ddc0 MH |
300 | } |
301 | ||
51f246ed TH |
302 | static void freezer_change_state(struct cgroup *cgroup, |
303 | enum freezer_state goal_state) | |
dc52ddc0 | 304 | { |
51f246ed | 305 | struct freezer *freezer = cgroup_freezer(cgroup); |
51308ee5 | 306 | |
dc52ddc0 | 307 | spin_lock_irq(&freezer->lock); |
51308ee5 | 308 | |
2d3cbf8b | 309 | update_if_frozen(cgroup, freezer); |
51308ee5 LZ |
310 | |
311 | switch (goal_state) { | |
81dcf33c | 312 | case CGROUP_THAWED: |
a3201227 TH |
313 | if (freezer->state != CGROUP_THAWED) |
314 | atomic_dec(&system_freezing_cnt); | |
22b4e111 | 315 | freezer->state = CGROUP_THAWED; |
51308ee5 | 316 | unfreeze_cgroup(cgroup, freezer); |
dc52ddc0 | 317 | break; |
81dcf33c | 318 | case CGROUP_FROZEN: |
a3201227 TH |
319 | if (freezer->state == CGROUP_THAWED) |
320 | atomic_inc(&system_freezing_cnt); | |
22b4e111 | 321 | freezer->state = CGROUP_FREEZING; |
51f246ed | 322 | freeze_cgroup(cgroup, freezer); |
dc52ddc0 MH |
323 | break; |
324 | default: | |
51308ee5 | 325 | BUG(); |
dc52ddc0 | 326 | } |
22b4e111 | 327 | |
dc52ddc0 | 328 | spin_unlock_irq(&freezer->lock); |
dc52ddc0 MH |
329 | } |
330 | ||
331 | static int freezer_write(struct cgroup *cgroup, | |
332 | struct cftype *cft, | |
333 | const char *buffer) | |
334 | { | |
dc52ddc0 MH |
335 | enum freezer_state goal_state; |
336 | ||
81dcf33c MH |
337 | if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0) |
338 | goal_state = CGROUP_THAWED; | |
339 | else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0) | |
340 | goal_state = CGROUP_FROZEN; | |
dc52ddc0 | 341 | else |
3b1b3f6e | 342 | return -EINVAL; |
dc52ddc0 MH |
343 | |
344 | if (!cgroup_lock_live_group(cgroup)) | |
345 | return -ENODEV; | |
51f246ed | 346 | freezer_change_state(cgroup, goal_state); |
dc52ddc0 | 347 | cgroup_unlock(); |
51f246ed | 348 | return 0; |
dc52ddc0 MH |
349 | } |
350 | ||
351 | static struct cftype files[] = { | |
352 | { | |
353 | .name = "state", | |
4baf6e33 | 354 | .flags = CFTYPE_NOT_ON_ROOT, |
dc52ddc0 MH |
355 | .read_seq_string = freezer_read, |
356 | .write_string = freezer_write, | |
357 | }, | |
4baf6e33 | 358 | { } /* terminate */ |
dc52ddc0 MH |
359 | }; |
360 | ||
dc52ddc0 MH |
361 | struct cgroup_subsys freezer_subsys = { |
362 | .name = "freezer", | |
363 | .create = freezer_create, | |
364 | .destroy = freezer_destroy, | |
dc52ddc0 | 365 | .subsys_id = freezer_subsys_id, |
8755ade6 | 366 | .attach = freezer_attach, |
dc52ddc0 | 367 | .fork = freezer_fork, |
4baf6e33 | 368 | .base_cftypes = files, |
8c7f6edb TH |
369 | |
370 | /* | |
371 | * freezer subsys doesn't handle hierarchy at all. Frozen state | |
372 | * should be inherited through the hierarchy - if a parent is | |
373 | * frozen, all its children should be frozen. Fix it and remove | |
374 | * the following. | |
375 | */ | |
376 | .broken_hierarchy = true, | |
dc52ddc0 | 377 | }; |