2 * cgroup_freezer.c - control group freezer subsystem
4 * Copyright IBM Corporation, 2007
6 * Author : Cedric Le Goater <clg@fr.ibm.com>
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.
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.
17 #include <linux/module.h>
18 #include <linux/cgroup.h>
20 #include <linux/uaccess.h>
21 #include <linux/freezer.h>
22 #include <linux/seq_file.h>
31 struct cgroup_subsys_state css;
32 enum freezer_state state;
33 spinlock_t lock; /* protects _writes_ to state */
36 static inline struct freezer *cgroup_freezer(
37 struct cgroup *cgroup)
40 cgroup_subsys_state(cgroup, freezer_subsys_id),
44 static inline struct freezer *task_freezer(struct task_struct *task)
46 return container_of(task_subsys_state(task, freezer_subsys_id),
50 int cgroup_frozen(struct task_struct *task)
52 struct freezer *freezer;
53 enum freezer_state state;
56 freezer = task_freezer(task);
57 state = freezer->state;
60 return state == STATE_FROZEN;
64 * cgroups_write_string() limits the size of freezer state strings to
65 * CGROUP_LOCAL_BUFFER_SIZE
67 static const char *freezer_state_strs[] = {
75 * Transitions are caused by userspace writes to the freezer.state file.
76 * The values in parenthesis are state labels. The rest are edge labels.
78 * (RUNNING) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
80 * | \_______RUNNING_______/ |
81 * \_____________________________RUNNING___________/
84 struct cgroup_subsys freezer_subsys;
86 /* Locks taken and their ordering
87 * ------------------------------
89 * cgroup_mutex (AKA cgroup_lock)
90 * task->alloc_lock (AKA task_lock)
92 * task->sighand->siglock
94 * cgroup code forces css_set_lock to be taken before task->alloc_lock
96 * freezer_create(), freezer_destroy():
97 * cgroup_mutex [ by cgroup core ]
103 * task->alloc_lock (to get task's cgroup)
105 * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
106 * task->alloc_lock (to get task's cgroup)
108 * sighand->siglock (if the cgroup is freezing)
113 * read_lock css_set_lock (cgroup iterator start)
115 * freezer_write() (freeze):
118 * read_lock css_set_lock (cgroup iterator start)
121 * freezer_write() (unfreeze):
124 * read_lock css_set_lock (cgroup iterator start)
125 * task->alloc_lock (to prevent races with freeze_task())
128 static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss,
129 struct cgroup *cgroup)
131 struct freezer *freezer;
133 freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
135 return ERR_PTR(-ENOMEM);
137 spin_lock_init(&freezer->lock);
138 freezer->state = STATE_RUNNING;
139 return &freezer->css;
142 static void freezer_destroy(struct cgroup_subsys *ss,
143 struct cgroup *cgroup)
145 kfree(cgroup_freezer(cgroup));
149 static int freezer_can_attach(struct cgroup_subsys *ss,
150 struct cgroup *new_cgroup,
151 struct task_struct *task)
153 struct freezer *freezer;
157 * The call to cgroup_lock() in the freezer.state write method prevents
158 * a write to that file racing against an attach, and hence the
159 * can_attach() result will remain valid until the attach completes.
161 freezer = cgroup_freezer(new_cgroup);
162 if (freezer->state == STATE_FROZEN)
167 static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
169 struct freezer *freezer;
172 freezer = task_freezer(task);
175 BUG_ON(freezer->state == STATE_FROZEN);
176 spin_lock_irq(&freezer->lock);
177 /* Locking avoids race with FREEZING -> RUNNING transitions. */
178 if (freezer->state == STATE_FREEZING)
179 freeze_task(task, true);
180 spin_unlock_irq(&freezer->lock);
184 * caller must hold freezer->lock
186 static void check_if_frozen(struct cgroup *cgroup,
187 struct freezer *freezer)
189 struct cgroup_iter it;
190 struct task_struct *task;
191 unsigned int nfrozen = 0, ntotal = 0;
193 cgroup_iter_start(cgroup, &it);
194 while ((task = cgroup_iter_next(cgroup, &it))) {
197 * Task is frozen or will freeze immediately when next it gets
201 (task_is_stopped_or_traced(task) && freezing(task)))
206 * Transition to FROZEN when no new tasks can be added ensures
207 * that we never exist in the FROZEN state while there are unfrozen
210 if (nfrozen == ntotal)
211 freezer->state = STATE_FROZEN;
212 cgroup_iter_end(cgroup, &it);
215 static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
218 struct freezer *freezer;
219 enum freezer_state state;
221 if (!cgroup_lock_live_group(cgroup))
224 freezer = cgroup_freezer(cgroup);
225 spin_lock_irq(&freezer->lock);
226 state = freezer->state;
227 if (state == STATE_FREEZING) {
228 /* We change from FREEZING to FROZEN lazily if the cgroup was
229 * only partially frozen when we exitted write. */
230 check_if_frozen(cgroup, freezer);
231 state = freezer->state;
233 spin_unlock_irq(&freezer->lock);
236 seq_puts(m, freezer_state_strs[state]);
241 static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
243 struct cgroup_iter it;
244 struct task_struct *task;
245 unsigned int num_cant_freeze_now = 0;
247 freezer->state = STATE_FREEZING;
248 cgroup_iter_start(cgroup, &it);
249 while ((task = cgroup_iter_next(cgroup, &it))) {
250 if (!freeze_task(task, true))
252 if (task_is_stopped_or_traced(task) && freezing(task))
254 * The freeze flag is set so these tasks will
255 * immediately go into the fridge upon waking.
258 if (!freezing(task) && !freezer_should_skip(task))
259 num_cant_freeze_now++;
261 cgroup_iter_end(cgroup, &it);
263 return num_cant_freeze_now ? -EBUSY : 0;
266 static int unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
268 struct cgroup_iter it;
269 struct task_struct *task;
271 cgroup_iter_start(cgroup, &it);
272 while ((task = cgroup_iter_next(cgroup, &it))) {
276 do_wake = __thaw_process(task);
279 wake_up_process(task);
281 cgroup_iter_end(cgroup, &it);
282 freezer->state = STATE_RUNNING;
287 static int freezer_change_state(struct cgroup *cgroup,
288 enum freezer_state goal_state)
290 struct freezer *freezer;
293 freezer = cgroup_freezer(cgroup);
294 spin_lock_irq(&freezer->lock);
295 check_if_frozen(cgroup, freezer); /* may update freezer->state */
296 if (goal_state == freezer->state)
298 switch (freezer->state) {
300 retval = try_to_freeze_cgroup(cgroup, freezer);
303 if (goal_state == STATE_FROZEN) {
304 /* Userspace is retrying after
305 * "/bin/echo FROZEN > freezer.state" returned -EBUSY */
306 retval = try_to_freeze_cgroup(cgroup, freezer);
309 /* state == FREEZING and goal_state == RUNNING, so unfreeze */
311 retval = unfreeze_cgroup(cgroup, freezer);
317 spin_unlock_irq(&freezer->lock);
322 static int freezer_write(struct cgroup *cgroup,
327 enum freezer_state goal_state;
329 if (strcmp(buffer, freezer_state_strs[STATE_RUNNING]) == 0)
330 goal_state = STATE_RUNNING;
331 else if (strcmp(buffer, freezer_state_strs[STATE_FROZEN]) == 0)
332 goal_state = STATE_FROZEN;
336 if (!cgroup_lock_live_group(cgroup))
338 retval = freezer_change_state(cgroup, goal_state);
343 static struct cftype files[] = {
346 .read_seq_string = freezer_read,
347 .write_string = freezer_write,
351 static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup)
353 return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
356 struct cgroup_subsys freezer_subsys = {
358 .create = freezer_create,
359 .destroy = freezer_destroy,
360 .populate = freezer_populate,
361 .subsys_id = freezer_subsys_id,
362 .can_attach = freezer_can_attach,
364 .fork = freezer_fork,