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[linux-2.6.git] / kernel / cgroup_freezer.c
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/module.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 static inline int __cgroup_freezing_or_frozen(struct task_struct *task)
52 {
53         enum freezer_state state = task_freezer(task)->state;
54         return (state == CGROUP_FREEZING) || (state == CGROUP_FROZEN);
55 }
56
57 int cgroup_freezing_or_frozen(struct task_struct *task)
58 {
59         int result;
60         task_lock(task);
61         result = __cgroup_freezing_or_frozen(task);
62         task_unlock(task);
63         return result;
64 }
65
66 /*
67  * cgroups_write_string() limits the size of freezer state strings to
68  * CGROUP_LOCAL_BUFFER_SIZE
69  */
70 static const char *freezer_state_strs[] = {
71         "THAWED",
72         "FREEZING",
73         "FROZEN",
74 };
75
76 /*
77  * State diagram
78  * Transitions are caused by userspace writes to the freezer.state file.
79  * The values in parenthesis are state labels. The rest are edge labels.
80  *
81  * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
82  *    ^ ^                    |                     |
83  *    | \_______THAWED_______/                     |
84  *    \__________________________THAWED____________/
85  */
86
87 struct cgroup_subsys freezer_subsys;
88
89 /* Locks taken and their ordering
90  * ------------------------------
91  * cgroup_mutex (AKA cgroup_lock)
92  * freezer->lock
93  * css_set_lock
94  * task->alloc_lock (AKA task_lock)
95  * task->sighand->siglock
96  *
97  * cgroup code forces css_set_lock to be taken before task->alloc_lock
98  *
99  * freezer_create(), freezer_destroy():
100  * cgroup_mutex [ by cgroup core ]
101  *
102  * freezer_can_attach():
103  * cgroup_mutex (held by caller of can_attach)
104  *
105  * cgroup_freezing_or_frozen():
106  * task->alloc_lock (to get task's cgroup)
107  *
108  * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
109  * freezer->lock
110  *  sighand->siglock (if the cgroup is freezing)
111  *
112  * freezer_read():
113  * cgroup_mutex
114  *  freezer->lock
115  *   write_lock css_set_lock (cgroup iterator start)
116  *    task->alloc_lock
117  *   read_lock css_set_lock (cgroup iterator start)
118  *
119  * freezer_write() (freeze):
120  * cgroup_mutex
121  *  freezer->lock
122  *   write_lock css_set_lock (cgroup iterator start)
123  *    task->alloc_lock
124  *   read_lock css_set_lock (cgroup iterator start)
125  *    sighand->siglock (fake signal delivery inside freeze_task())
126  *
127  * freezer_write() (unfreeze):
128  * cgroup_mutex
129  *  freezer->lock
130  *   write_lock css_set_lock (cgroup iterator start)
131  *    task->alloc_lock
132  *   read_lock css_set_lock (cgroup iterator start)
133  *    task->alloc_lock (inside thaw_process(), prevents race with refrigerator())
134  *     sighand->siglock
135  */
136 static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss,
137                                                   struct cgroup *cgroup)
138 {
139         struct freezer *freezer;
140
141         freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
142         if (!freezer)
143                 return ERR_PTR(-ENOMEM);
144
145         spin_lock_init(&freezer->lock);
146         freezer->state = CGROUP_THAWED;
147         return &freezer->css;
148 }
149
150 static void freezer_destroy(struct cgroup_subsys *ss,
151                             struct cgroup *cgroup)
152 {
153         kfree(cgroup_freezer(cgroup));
154 }
155
156 /* task is frozen or will freeze immediately when next it gets woken */
157 static bool is_task_frozen_enough(struct task_struct *task)
158 {
159         return frozen(task) ||
160                 (task_is_stopped_or_traced(task) && freezing(task));
161 }
162
163 /*
164  * The call to cgroup_lock() in the freezer.state write method prevents
165  * a write to that file racing against an attach, and hence the
166  * can_attach() result will remain valid until the attach completes.
167  */
168 static int freezer_can_attach(struct cgroup_subsys *ss,
169                               struct cgroup *new_cgroup,
170                               struct task_struct *task)
171 {
172         struct freezer *freezer;
173
174         /*
175          * Anything frozen can't move or be moved to/from.
176          */
177
178         freezer = cgroup_freezer(new_cgroup);
179         if (freezer->state != CGROUP_THAWED)
180                 return -EBUSY;
181
182         return 0;
183 }
184
185 static int freezer_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
186 {
187         rcu_read_lock();
188         if (__cgroup_freezing_or_frozen(tsk)) {
189                 rcu_read_unlock();
190                 return -EBUSY;
191         }
192         rcu_read_unlock();
193         return 0;
194 }
195
196 static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
197 {
198         struct freezer *freezer;
199
200         /*
201          * No lock is needed, since the task isn't on tasklist yet,
202          * so it can't be moved to another cgroup, which means the
203          * freezer won't be removed and will be valid during this
204          * function call.  Nevertheless, apply RCU read-side critical
205          * section to suppress RCU lockdep false positives.
206          */
207         rcu_read_lock();
208         freezer = task_freezer(task);
209         rcu_read_unlock();
210
211         /*
212          * The root cgroup is non-freezable, so we can skip the
213          * following check.
214          */
215         if (!freezer->css.cgroup->parent)
216                 return;
217
218         spin_lock_irq(&freezer->lock);
219         BUG_ON(freezer->state == CGROUP_FROZEN);
220
221         /* Locking avoids race with FREEZING -> THAWED transitions. */
222         if (freezer->state == CGROUP_FREEZING)
223                 freeze_task(task, true);
224         spin_unlock_irq(&freezer->lock);
225 }
226
227 /*
228  * caller must hold freezer->lock
229  */
230 static void update_if_frozen(struct cgroup *cgroup,
231                                  struct freezer *freezer)
232 {
233         struct cgroup_iter it;
234         struct task_struct *task;
235         unsigned int nfrozen = 0, ntotal = 0;
236         enum freezer_state old_state = freezer->state;
237
238         cgroup_iter_start(cgroup, &it);
239         while ((task = cgroup_iter_next(cgroup, &it))) {
240                 ntotal++;
241                 if (is_task_frozen_enough(task))
242                         nfrozen++;
243         }
244
245         if (old_state == CGROUP_THAWED) {
246                 BUG_ON(nfrozen > 0);
247         } else if (old_state == CGROUP_FREEZING) {
248                 if (nfrozen == ntotal)
249                         freezer->state = CGROUP_FROZEN;
250         } else { /* old_state == CGROUP_FROZEN */
251                 BUG_ON(nfrozen != ntotal);
252         }
253
254         cgroup_iter_end(cgroup, &it);
255 }
256
257 static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
258                         struct seq_file *m)
259 {
260         struct freezer *freezer;
261         enum freezer_state state;
262
263         if (!cgroup_lock_live_group(cgroup))
264                 return -ENODEV;
265
266         freezer = cgroup_freezer(cgroup);
267         spin_lock_irq(&freezer->lock);
268         state = freezer->state;
269         if (state == CGROUP_FREEZING) {
270                 /* We change from FREEZING to FROZEN lazily if the cgroup was
271                  * only partially frozen when we exitted write. */
272                 update_if_frozen(cgroup, freezer);
273                 state = freezer->state;
274         }
275         spin_unlock_irq(&freezer->lock);
276         cgroup_unlock();
277
278         seq_puts(m, freezer_state_strs[state]);
279         seq_putc(m, '\n');
280         return 0;
281 }
282
283 static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
284 {
285         struct cgroup_iter it;
286         struct task_struct *task;
287         unsigned int num_cant_freeze_now = 0;
288
289         freezer->state = CGROUP_FREEZING;
290         cgroup_iter_start(cgroup, &it);
291         while ((task = cgroup_iter_next(cgroup, &it))) {
292                 if (!freeze_task(task, true))
293                         continue;
294                 if (is_task_frozen_enough(task))
295                         continue;
296                 if (!freezing(task) && !freezer_should_skip(task))
297                         num_cant_freeze_now++;
298         }
299         cgroup_iter_end(cgroup, &it);
300
301         return num_cant_freeze_now ? -EBUSY : 0;
302 }
303
304 static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
305 {
306         struct cgroup_iter it;
307         struct task_struct *task;
308
309         cgroup_iter_start(cgroup, &it);
310         while ((task = cgroup_iter_next(cgroup, &it))) {
311                 thaw_process(task);
312         }
313         cgroup_iter_end(cgroup, &it);
314
315         freezer->state = CGROUP_THAWED;
316 }
317
318 static int freezer_change_state(struct cgroup *cgroup,
319                                 enum freezer_state goal_state)
320 {
321         struct freezer *freezer;
322         int retval = 0;
323
324         freezer = cgroup_freezer(cgroup);
325
326         spin_lock_irq(&freezer->lock);
327
328         update_if_frozen(cgroup, freezer);
329         if (goal_state == freezer->state)
330                 goto out;
331
332         switch (goal_state) {
333         case CGROUP_THAWED:
334                 unfreeze_cgroup(cgroup, freezer);
335                 break;
336         case CGROUP_FROZEN:
337                 retval = try_to_freeze_cgroup(cgroup, freezer);
338                 break;
339         default:
340                 BUG();
341         }
342 out:
343         spin_unlock_irq(&freezer->lock);
344
345         return retval;
346 }
347
348 static int freezer_write(struct cgroup *cgroup,
349                          struct cftype *cft,
350                          const char *buffer)
351 {
352         int retval;
353         enum freezer_state goal_state;
354
355         if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
356                 goal_state = CGROUP_THAWED;
357         else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
358                 goal_state = CGROUP_FROZEN;
359         else
360                 return -EINVAL;
361
362         if (!cgroup_lock_live_group(cgroup))
363                 return -ENODEV;
364         retval = freezer_change_state(cgroup, goal_state);
365         cgroup_unlock();
366         return retval;
367 }
368
369 static struct cftype files[] = {
370         {
371                 .name = "state",
372                 .read_seq_string = freezer_read,
373                 .write_string = freezer_write,
374         },
375 };
376
377 static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup)
378 {
379         if (!cgroup->parent)
380                 return 0;
381         return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
382 }
383
384 struct cgroup_subsys freezer_subsys = {
385         .name           = "freezer",
386         .create         = freezer_create,
387         .destroy        = freezer_destroy,
388         .populate       = freezer_populate,
389         .subsys_id      = freezer_subsys_id,
390         .can_attach     = freezer_can_attach,
391         .can_attach_task = freezer_can_attach_task,
392         .pre_attach     = NULL,
393         .attach_task    = NULL,
394         .attach         = NULL,
395         .fork           = freezer_fork,
396         .exit           = NULL,
397 };