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/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 int cgroup_frozen(struct task_struct
*task
)
53 struct freezer
*freezer
;
54 enum freezer_state state
;
57 freezer
= task_freezer(task
);
58 state
= freezer
->state
;
61 return 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 * ------------------------------
90 * cgroup_mutex (AKA cgroup_lock)
91 * 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 ]
104 * task->alloc_lock (to get task's cgroup)
106 * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
107 * task->alloc_lock (to get task's cgroup)
109 * sighand->siglock (if the cgroup is freezing)
114 * read_lock css_set_lock (cgroup iterator start)
116 * freezer_write() (freeze):
119 * read_lock css_set_lock (cgroup iterator start)
122 * freezer_write() (unfreeze):
125 * read_lock css_set_lock (cgroup iterator start)
126 * task->alloc_lock (to prevent races with freeze_task())
129 static struct cgroup_subsys_state
*freezer_create(struct cgroup_subsys
*ss
,
130 struct cgroup
*cgroup
)
132 struct freezer
*freezer
;
134 freezer
= kzalloc(sizeof(struct freezer
), GFP_KERNEL
);
136 return ERR_PTR(-ENOMEM
);
138 spin_lock_init(&freezer
->lock
);
139 freezer
->state
= CGROUP_THAWED
;
140 return &freezer
->css
;
143 static void freezer_destroy(struct cgroup_subsys
*ss
,
144 struct cgroup
*cgroup
)
146 kfree(cgroup_freezer(cgroup
));
149 /* Task is frozen or will freeze immediately when next it gets woken */
150 static bool is_task_frozen_enough(struct task_struct
*task
)
152 return frozen(task
) ||
153 (task_is_stopped_or_traced(task
) && freezing(task
));
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 static int freezer_can_attach(struct cgroup_subsys
*ss
,
162 struct cgroup
*new_cgroup
,
163 struct task_struct
*task
, bool threadgroup
)
165 struct freezer
*freezer
;
168 * Anything frozen can't move or be moved to/from.
170 * Since orig_freezer->state == FROZEN means that @task has been
171 * frozen, so it's sufficient to check the latter condition.
174 if (is_task_frozen_enough(task
))
177 freezer
= cgroup_freezer(new_cgroup
);
178 if (freezer
->state
== CGROUP_FROZEN
)
182 struct task_struct
*c
;
185 list_for_each_entry_rcu(c
, &task
->thread_group
, thread_group
) {
186 if (is_task_frozen_enough(c
)) {
197 static void freezer_fork(struct cgroup_subsys
*ss
, struct task_struct
*task
)
199 struct freezer
*freezer
;
202 * No lock is needed, since the task isn't on tasklist yet,
203 * so it can't be moved to another cgroup, which means the
204 * freezer won't be removed and will be valid during this
207 freezer
= task_freezer(task
);
210 * The root cgroup is non-freezable, so we can skip the
213 if (!freezer
->css
.cgroup
->parent
)
216 spin_lock_irq(&freezer
->lock
);
217 BUG_ON(freezer
->state
== CGROUP_FROZEN
);
219 /* Locking avoids race with FREEZING -> THAWED transitions. */
220 if (freezer
->state
== CGROUP_FREEZING
)
221 freeze_task(task
, true);
222 spin_unlock_irq(&freezer
->lock
);
226 * caller must hold freezer->lock
228 static void update_freezer_state(struct cgroup
*cgroup
,
229 struct freezer
*freezer
)
231 struct cgroup_iter it
;
232 struct task_struct
*task
;
233 unsigned int nfrozen
= 0, ntotal
= 0;
235 cgroup_iter_start(cgroup
, &it
);
236 while ((task
= cgroup_iter_next(cgroup
, &it
))) {
238 if (is_task_frozen_enough(task
))
243 * Transition to FROZEN when no new tasks can be added ensures
244 * that we never exist in the FROZEN state while there are unfrozen
247 if (nfrozen
== ntotal
)
248 freezer
->state
= CGROUP_FROZEN
;
249 else if (nfrozen
> 0)
250 freezer
->state
= CGROUP_FREEZING
;
252 freezer
->state
= CGROUP_THAWED
;
253 cgroup_iter_end(cgroup
, &it
);
256 static int freezer_read(struct cgroup
*cgroup
, struct cftype
*cft
,
259 struct freezer
*freezer
;
260 enum freezer_state state
;
262 if (!cgroup_lock_live_group(cgroup
))
265 freezer
= cgroup_freezer(cgroup
);
266 spin_lock_irq(&freezer
->lock
);
267 state
= freezer
->state
;
268 if (state
== CGROUP_FREEZING
) {
269 /* We change from FREEZING to FROZEN lazily if the cgroup was
270 * only partially frozen when we exitted write. */
271 update_freezer_state(cgroup
, freezer
);
272 state
= freezer
->state
;
274 spin_unlock_irq(&freezer
->lock
);
277 seq_puts(m
, freezer_state_strs
[state
]);
282 static int try_to_freeze_cgroup(struct cgroup
*cgroup
, struct freezer
*freezer
)
284 struct cgroup_iter it
;
285 struct task_struct
*task
;
286 unsigned int num_cant_freeze_now
= 0;
288 freezer
->state
= CGROUP_FREEZING
;
289 cgroup_iter_start(cgroup
, &it
);
290 while ((task
= cgroup_iter_next(cgroup
, &it
))) {
291 if (!freeze_task(task
, true))
293 if (is_task_frozen_enough(task
))
295 if (!freezing(task
) && !freezer_should_skip(task
))
296 num_cant_freeze_now
++;
298 cgroup_iter_end(cgroup
, &it
);
300 return num_cant_freeze_now
? -EBUSY
: 0;
303 static void unfreeze_cgroup(struct cgroup
*cgroup
, struct freezer
*freezer
)
305 struct cgroup_iter it
;
306 struct task_struct
*task
;
308 cgroup_iter_start(cgroup
, &it
);
309 while ((task
= cgroup_iter_next(cgroup
, &it
))) {
312 cgroup_iter_end(cgroup
, &it
);
314 freezer
->state
= CGROUP_THAWED
;
317 static int freezer_change_state(struct cgroup
*cgroup
,
318 enum freezer_state goal_state
)
320 struct freezer
*freezer
;
323 freezer
= cgroup_freezer(cgroup
);
325 spin_lock_irq(&freezer
->lock
);
327 update_freezer_state(cgroup
, freezer
);
328 if (goal_state
== freezer
->state
)
331 switch (goal_state
) {
333 unfreeze_cgroup(cgroup
, freezer
);
336 retval
= try_to_freeze_cgroup(cgroup
, freezer
);
342 spin_unlock_irq(&freezer
->lock
);
347 static int freezer_write(struct cgroup
*cgroup
,
352 enum freezer_state goal_state
;
354 if (strcmp(buffer
, freezer_state_strs
[CGROUP_THAWED
]) == 0)
355 goal_state
= CGROUP_THAWED
;
356 else if (strcmp(buffer
, freezer_state_strs
[CGROUP_FROZEN
]) == 0)
357 goal_state
= CGROUP_FROZEN
;
361 if (!cgroup_lock_live_group(cgroup
))
363 retval
= freezer_change_state(cgroup
, goal_state
);
368 static struct cftype files
[] = {
371 .read_seq_string
= freezer_read
,
372 .write_string
= freezer_write
,
376 static int freezer_populate(struct cgroup_subsys
*ss
, struct cgroup
*cgroup
)
380 return cgroup_add_files(cgroup
, ss
, files
, ARRAY_SIZE(files
));
383 struct cgroup_subsys freezer_subsys
= {
385 .create
= freezer_create
,
386 .destroy
= freezer_destroy
,
387 .populate
= freezer_populate
,
388 .subsys_id
= freezer_subsys_id
,
389 .can_attach
= freezer_can_attach
,
391 .fork
= freezer_fork
,