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_freezing_or_frozen(struct task_struct
*task
)
53 struct freezer
*freezer
;
54 enum freezer_state state
;
57 freezer
= task_freezer(task
);
58 if (!freezer
->css
.cgroup
->parent
)
59 state
= CGROUP_THAWED
; /* root cgroup can't be frozen */
61 state
= freezer
->state
;
64 return (state
== CGROUP_FREEZING
) || (state
== CGROUP_FROZEN
);
68 * cgroups_write_string() limits the size of freezer state strings to
69 * CGROUP_LOCAL_BUFFER_SIZE
71 static const char *freezer_state_strs
[] = {
79 * Transitions are caused by userspace writes to the freezer.state file.
80 * The values in parenthesis are state labels. The rest are edge labels.
82 * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
84 * | \_______THAWED_______/ |
85 * \__________________________THAWED____________/
88 struct cgroup_subsys freezer_subsys
;
90 /* Locks taken and their ordering
91 * ------------------------------
93 * cgroup_mutex (AKA cgroup_lock)
94 * task->alloc_lock (AKA task_lock)
96 * task->sighand->siglock
98 * cgroup code forces css_set_lock to be taken before task->alloc_lock
100 * freezer_create(), freezer_destroy():
101 * cgroup_mutex [ by cgroup core ]
107 * task->alloc_lock (to get task's cgroup)
109 * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
110 * task->alloc_lock (to get task's cgroup)
112 * sighand->siglock (if the cgroup is freezing)
117 * read_lock css_set_lock (cgroup iterator start)
119 * freezer_write() (freeze):
122 * read_lock css_set_lock (cgroup iterator start)
125 * freezer_write() (unfreeze):
128 * read_lock css_set_lock (cgroup iterator start)
129 * task->alloc_lock (to prevent races with freeze_task())
132 static struct cgroup_subsys_state
*freezer_create(struct cgroup_subsys
*ss
,
133 struct cgroup
*cgroup
)
135 struct freezer
*freezer
;
137 freezer
= kzalloc(sizeof(struct freezer
), GFP_KERNEL
);
139 return ERR_PTR(-ENOMEM
);
141 spin_lock_init(&freezer
->lock
);
142 freezer
->state
= CGROUP_THAWED
;
143 return &freezer
->css
;
146 static void freezer_destroy(struct cgroup_subsys
*ss
,
147 struct cgroup
*cgroup
)
149 kfree(cgroup_freezer(cgroup
));
152 /* Task is frozen or will freeze immediately when next it gets woken */
153 static bool is_task_frozen_enough(struct task_struct
*task
)
155 return frozen(task
) ||
156 (task_is_stopped_or_traced(task
) && freezing(task
));
160 * The call to cgroup_lock() in the freezer.state write method prevents
161 * a write to that file racing against an attach, and hence the
162 * can_attach() result will remain valid until the attach completes.
164 static int freezer_can_attach(struct cgroup_subsys
*ss
,
165 struct cgroup
*new_cgroup
,
166 struct task_struct
*task
, bool threadgroup
)
168 struct freezer
*freezer
;
171 * Anything frozen can't move or be moved to/from.
173 * Since orig_freezer->state == FROZEN means that @task has been
174 * frozen, so it's sufficient to check the latter condition.
177 if (is_task_frozen_enough(task
))
180 freezer
= cgroup_freezer(new_cgroup
);
181 if (freezer
->state
== CGROUP_FROZEN
)
185 struct task_struct
*c
;
188 list_for_each_entry_rcu(c
, &task
->thread_group
, thread_group
) {
189 if (is_task_frozen_enough(c
)) {
200 static void freezer_fork(struct cgroup_subsys
*ss
, struct task_struct
*task
)
202 struct freezer
*freezer
;
205 * No lock is needed, since the task isn't on tasklist yet,
206 * so it can't be moved to another cgroup, which means the
207 * freezer won't be removed and will be valid during this
208 * function call. Nevertheless, apply RCU read-side critical
209 * section to suppress RCU lockdep false positives.
212 freezer
= task_freezer(task
);
216 * The root cgroup is non-freezable, so we can skip the
219 if (!freezer
->css
.cgroup
->parent
)
222 spin_lock_irq(&freezer
->lock
);
223 BUG_ON(freezer
->state
== CGROUP_FROZEN
);
225 /* Locking avoids race with FREEZING -> THAWED transitions. */
226 if (freezer
->state
== CGROUP_FREEZING
)
227 freeze_task(task
, true);
228 spin_unlock_irq(&freezer
->lock
);
232 * caller must hold freezer->lock
234 static void update_freezer_state(struct cgroup
*cgroup
,
235 struct freezer
*freezer
)
237 struct cgroup_iter it
;
238 struct task_struct
*task
;
239 unsigned int nfrozen
= 0, ntotal
= 0;
241 cgroup_iter_start(cgroup
, &it
);
242 while ((task
= cgroup_iter_next(cgroup
, &it
))) {
244 if (is_task_frozen_enough(task
))
249 * Transition to FROZEN when no new tasks can be added ensures
250 * that we never exist in the FROZEN state while there are unfrozen
253 if (nfrozen
== ntotal
)
254 freezer
->state
= CGROUP_FROZEN
;
255 else if (nfrozen
> 0)
256 freezer
->state
= CGROUP_FREEZING
;
258 freezer
->state
= CGROUP_THAWED
;
259 cgroup_iter_end(cgroup
, &it
);
262 static int freezer_read(struct cgroup
*cgroup
, struct cftype
*cft
,
265 struct freezer
*freezer
;
266 enum freezer_state state
;
268 if (!cgroup_lock_live_group(cgroup
))
271 freezer
= cgroup_freezer(cgroup
);
272 spin_lock_irq(&freezer
->lock
);
273 state
= freezer
->state
;
274 if (state
== CGROUP_FREEZING
) {
275 /* We change from FREEZING to FROZEN lazily if the cgroup was
276 * only partially frozen when we exitted write. */
277 update_freezer_state(cgroup
, freezer
);
278 state
= freezer
->state
;
280 spin_unlock_irq(&freezer
->lock
);
283 seq_puts(m
, freezer_state_strs
[state
]);
288 static int try_to_freeze_cgroup(struct cgroup
*cgroup
, struct freezer
*freezer
)
290 struct cgroup_iter it
;
291 struct task_struct
*task
;
292 unsigned int num_cant_freeze_now
= 0;
294 freezer
->state
= CGROUP_FREEZING
;
295 cgroup_iter_start(cgroup
, &it
);
296 while ((task
= cgroup_iter_next(cgroup
, &it
))) {
297 if (!freeze_task(task
, true))
299 if (is_task_frozen_enough(task
))
301 if (!freezing(task
) && !freezer_should_skip(task
))
302 num_cant_freeze_now
++;
304 cgroup_iter_end(cgroup
, &it
);
306 return num_cant_freeze_now
? -EBUSY
: 0;
309 static void unfreeze_cgroup(struct cgroup
*cgroup
, struct freezer
*freezer
)
311 struct cgroup_iter it
;
312 struct task_struct
*task
;
314 cgroup_iter_start(cgroup
, &it
);
315 while ((task
= cgroup_iter_next(cgroup
, &it
))) {
318 cgroup_iter_end(cgroup
, &it
);
320 freezer
->state
= CGROUP_THAWED
;
323 static int freezer_change_state(struct cgroup
*cgroup
,
324 enum freezer_state goal_state
)
326 struct freezer
*freezer
;
329 freezer
= cgroup_freezer(cgroup
);
331 spin_lock_irq(&freezer
->lock
);
333 update_freezer_state(cgroup
, freezer
);
334 if (goal_state
== freezer
->state
)
337 switch (goal_state
) {
339 unfreeze_cgroup(cgroup
, freezer
);
342 retval
= try_to_freeze_cgroup(cgroup
, freezer
);
348 spin_unlock_irq(&freezer
->lock
);
353 static int freezer_write(struct cgroup
*cgroup
,
358 enum freezer_state goal_state
;
360 if (strcmp(buffer
, freezer_state_strs
[CGROUP_THAWED
]) == 0)
361 goal_state
= CGROUP_THAWED
;
362 else if (strcmp(buffer
, freezer_state_strs
[CGROUP_FROZEN
]) == 0)
363 goal_state
= CGROUP_FROZEN
;
367 if (!cgroup_lock_live_group(cgroup
))
369 retval
= freezer_change_state(cgroup
, goal_state
);
374 static struct cftype files
[] = {
377 .read_seq_string
= freezer_read
,
378 .write_string
= freezer_write
,
382 static int freezer_populate(struct cgroup_subsys
*ss
, struct cgroup
*cgroup
)
386 return cgroup_add_files(cgroup
, ss
, files
, ARRAY_SIZE(files
));
389 struct cgroup_subsys freezer_subsys
= {
391 .create
= freezer_create
,
392 .destroy
= freezer_destroy
,
393 .populate
= freezer_populate
,
394 .subsys_id
= freezer_subsys_id
,
395 .can_attach
= freezer_can_attach
,
397 .fork
= freezer_fork
,