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/export.h>
18 #include <linux/slab.h>
19 #include <linux/cgroup.h>
21 #include <linux/uaccess.h>
22 #include <linux/freezer.h>
23 #include <linux/seq_file.h>
32 struct cgroup_subsys_state css;
33 enum freezer_state state;
34 spinlock_t lock; /* protects _writes_ to state */
37 static inline struct freezer *cgroup_freezer(
38 struct cgroup *cgroup)
41 cgroup_subsys_state(cgroup, freezer_subsys_id),
45 static inline struct freezer *task_freezer(struct task_struct *task)
47 return container_of(task_subsys_state(task, freezer_subsys_id),
51 bool cgroup_freezing(struct task_struct *task)
53 enum freezer_state state;
57 state = task_freezer(task)->state;
58 ret = state == CGROUP_FREEZING || state == CGROUP_FROZEN;
65 * cgroups_write_string() limits the size of freezer state strings to
66 * CGROUP_LOCAL_BUFFER_SIZE
68 static const char *freezer_state_strs[] = {
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.
79 * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
81 * | \_______THAWED_______/ |
82 * \__________________________THAWED____________/
85 struct cgroup_subsys freezer_subsys;
87 /* Locks taken and their ordering
88 * ------------------------------
89 * cgroup_mutex (AKA cgroup_lock)
92 * task->alloc_lock (AKA task_lock)
93 * task->sighand->siglock
95 * cgroup code forces css_set_lock to be taken before task->alloc_lock
97 * freezer_create(), freezer_destroy():
98 * cgroup_mutex [ by cgroup core ]
100 * freezer_can_attach():
101 * cgroup_mutex (held by caller of can_attach)
103 * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
105 * sighand->siglock (if the cgroup is freezing)
110 * write_lock css_set_lock (cgroup iterator start)
112 * read_lock css_set_lock (cgroup iterator start)
114 * freezer_write() (freeze):
117 * write_lock css_set_lock (cgroup iterator start)
119 * read_lock css_set_lock (cgroup iterator start)
120 * sighand->siglock (fake signal delivery inside freeze_task())
122 * freezer_write() (unfreeze):
125 * write_lock css_set_lock (cgroup iterator start)
127 * read_lock css_set_lock (cgroup iterator start)
128 * task->alloc_lock (inside __thaw_task(), prevents race with refrigerator())
131 static struct cgroup_subsys_state *freezer_create(struct cgroup *cgroup)
133 struct freezer *freezer;
135 freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
137 return ERR_PTR(-ENOMEM);
139 spin_lock_init(&freezer->lock);
140 freezer->state = CGROUP_THAWED;
141 return &freezer->css;
144 static void freezer_destroy(struct cgroup *cgroup)
146 struct freezer *freezer = cgroup_freezer(cgroup);
148 if (freezer->state != CGROUP_THAWED)
149 atomic_dec(&system_freezing_cnt);
154 * The call to cgroup_lock() in the freezer.state write method prevents
155 * a write to that file racing against an attach, and hence we don't need
156 * to worry about racing against migration.
158 static void freezer_attach(struct cgroup *new_cgrp, struct cgroup_taskset *tset)
160 struct freezer *freezer = cgroup_freezer(new_cgrp);
161 struct task_struct *task;
163 spin_lock_irq(&freezer->lock);
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.
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.
177 cgroup_taskset_for_each(task, new_cgrp, tset) {
178 if (freezer->state == CGROUP_THAWED) {
182 freezer->state = CGROUP_FREEZING;
186 spin_unlock_irq(&freezer->lock);
189 static void freezer_fork(struct task_struct *task)
191 struct freezer *freezer;
194 freezer = task_freezer(task);
197 * The root cgroup is non-freezable, so we can skip the
200 if (!freezer->css.cgroup->parent)
203 spin_lock_irq(&freezer->lock);
205 * @task might have been just migrated into a FROZEN cgroup. Test
206 * equality with THAWED. Read the comment in freezer_attach().
208 if (freezer->state != CGROUP_THAWED)
210 spin_unlock_irq(&freezer->lock);
216 * caller must hold freezer->lock
218 static void update_if_frozen(struct cgroup *cgroup,
219 struct freezer *freezer)
221 struct cgroup_iter it;
222 struct task_struct *task;
223 unsigned int nfrozen = 0, ntotal = 0;
224 enum freezer_state old_state = freezer->state;
226 cgroup_iter_start(cgroup, &it);
227 while ((task = cgroup_iter_next(cgroup, &it))) {
228 if (freezing(task)) {
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.
236 if (frozen(task) || task_is_stopped_or_traced(task) ||
237 freezer_should_skip(task))
242 if (old_state == CGROUP_THAWED) {
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);
251 cgroup_iter_end(cgroup, &it);
254 static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
257 struct freezer *freezer;
258 enum freezer_state state;
260 if (!cgroup_lock_live_group(cgroup))
263 freezer = cgroup_freezer(cgroup);
264 spin_lock_irq(&freezer->lock);
265 state = freezer->state;
266 if (state == CGROUP_FREEZING) {
267 /* We change from FREEZING to FROZEN lazily if the cgroup was
268 * only partially frozen when we exitted write. */
269 update_if_frozen(cgroup, freezer);
270 state = freezer->state;
272 spin_unlock_irq(&freezer->lock);
275 seq_puts(m, freezer_state_strs[state]);
280 static void freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
282 struct cgroup_iter it;
283 struct task_struct *task;
285 cgroup_iter_start(cgroup, &it);
286 while ((task = cgroup_iter_next(cgroup, &it)))
288 cgroup_iter_end(cgroup, &it);
291 static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
293 struct cgroup_iter it;
294 struct task_struct *task;
296 cgroup_iter_start(cgroup, &it);
297 while ((task = cgroup_iter_next(cgroup, &it)))
299 cgroup_iter_end(cgroup, &it);
302 static void freezer_change_state(struct cgroup *cgroup,
303 enum freezer_state goal_state)
305 struct freezer *freezer = cgroup_freezer(cgroup);
307 spin_lock_irq(&freezer->lock);
309 update_if_frozen(cgroup, freezer);
311 switch (goal_state) {
313 if (freezer->state != CGROUP_THAWED)
314 atomic_dec(&system_freezing_cnt);
315 freezer->state = CGROUP_THAWED;
316 unfreeze_cgroup(cgroup, freezer);
319 if (freezer->state == CGROUP_THAWED)
320 atomic_inc(&system_freezing_cnt);
321 freezer->state = CGROUP_FREEZING;
322 freeze_cgroup(cgroup, freezer);
328 spin_unlock_irq(&freezer->lock);
331 static int freezer_write(struct cgroup *cgroup,
335 enum freezer_state goal_state;
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;
344 if (!cgroup_lock_live_group(cgroup))
346 freezer_change_state(cgroup, goal_state);
351 static struct cftype files[] = {
354 .flags = CFTYPE_NOT_ON_ROOT,
355 .read_seq_string = freezer_read,
356 .write_string = freezer_write,
361 struct cgroup_subsys freezer_subsys = {
363 .create = freezer_create,
364 .destroy = freezer_destroy,
365 .subsys_id = freezer_subsys_id,
366 .attach = freezer_attach,
367 .fork = freezer_fork,
368 .base_cftypes = files,
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
376 .broken_hierarchy = true,