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_subsys
*ss
,
132 struct cgroup
*cgroup
)
134 struct freezer
*freezer
;
136 freezer
= kzalloc(sizeof(struct freezer
), GFP_KERNEL
);
138 return ERR_PTR(-ENOMEM
);
140 spin_lock_init(&freezer
->lock
);
141 freezer
->state
= CGROUP_THAWED
;
142 return &freezer
->css
;
145 static void freezer_destroy(struct cgroup_subsys
*ss
,
146 struct cgroup
*cgroup
)
148 struct freezer
*freezer
= cgroup_freezer(cgroup
);
150 if (freezer
->state
!= CGROUP_THAWED
)
151 atomic_dec(&system_freezing_cnt
);
155 /* task is frozen or will freeze immediately when next it gets woken */
156 static bool is_task_frozen_enough(struct task_struct
*task
)
158 return frozen(task
) ||
159 (task_is_stopped_or_traced(task
) && freezing(task
));
163 * The call to cgroup_lock() in the freezer.state write method prevents
164 * a write to that file racing against an attach, and hence the
165 * can_attach() result will remain valid until the attach completes.
167 static int freezer_can_attach(struct cgroup_subsys
*ss
,
168 struct cgroup
*new_cgroup
,
169 struct task_struct
*task
)
171 struct freezer
*freezer
;
174 * Anything frozen can't move or be moved to/from.
177 freezer
= cgroup_freezer(new_cgroup
);
178 if (freezer
->state
!= CGROUP_THAWED
)
184 static int freezer_can_attach_task(struct cgroup
*cgrp
, struct task_struct
*tsk
)
186 return cgroup_freezing(tsk
) ? -EBUSY
: 0;
189 static void freezer_fork(struct cgroup_subsys
*ss
, struct task_struct
*task
)
191 struct freezer
*freezer
;
194 * No lock is needed, since the task isn't on tasklist yet,
195 * so it can't be moved to another cgroup, which means the
196 * freezer won't be removed and will be valid during this
197 * function call. Nevertheless, apply RCU read-side critical
198 * section to suppress RCU lockdep false positives.
201 freezer
= task_freezer(task
);
205 * The root cgroup is non-freezable, so we can skip the
208 if (!freezer
->css
.cgroup
->parent
)
211 spin_lock_irq(&freezer
->lock
);
212 BUG_ON(freezer
->state
== CGROUP_FROZEN
);
214 /* Locking avoids race with FREEZING -> THAWED transitions. */
215 if (freezer
->state
== CGROUP_FREEZING
)
217 spin_unlock_irq(&freezer
->lock
);
221 * caller must hold freezer->lock
223 static void update_if_frozen(struct cgroup
*cgroup
,
224 struct freezer
*freezer
)
226 struct cgroup_iter it
;
227 struct task_struct
*task
;
228 unsigned int nfrozen
= 0, ntotal
= 0;
229 enum freezer_state old_state
= freezer
->state
;
231 cgroup_iter_start(cgroup
, &it
);
232 while ((task
= cgroup_iter_next(cgroup
, &it
))) {
234 if (freezing(task
) && is_task_frozen_enough(task
))
238 if (old_state
== CGROUP_THAWED
) {
240 } else if (old_state
== CGROUP_FREEZING
) {
241 if (nfrozen
== ntotal
)
242 freezer
->state
= CGROUP_FROZEN
;
243 } else { /* old_state == CGROUP_FROZEN */
244 BUG_ON(nfrozen
!= ntotal
);
247 cgroup_iter_end(cgroup
, &it
);
250 static int freezer_read(struct cgroup
*cgroup
, struct cftype
*cft
,
253 struct freezer
*freezer
;
254 enum freezer_state state
;
256 if (!cgroup_lock_live_group(cgroup
))
259 freezer
= cgroup_freezer(cgroup
);
260 spin_lock_irq(&freezer
->lock
);
261 state
= freezer
->state
;
262 if (state
== CGROUP_FREEZING
) {
263 /* We change from FREEZING to FROZEN lazily if the cgroup was
264 * only partially frozen when we exitted write. */
265 update_if_frozen(cgroup
, freezer
);
266 state
= freezer
->state
;
268 spin_unlock_irq(&freezer
->lock
);
271 seq_puts(m
, freezer_state_strs
[state
]);
276 static int try_to_freeze_cgroup(struct cgroup
*cgroup
, struct freezer
*freezer
)
278 struct cgroup_iter it
;
279 struct task_struct
*task
;
280 unsigned int num_cant_freeze_now
= 0;
282 cgroup_iter_start(cgroup
, &it
);
283 while ((task
= cgroup_iter_next(cgroup
, &it
))) {
284 if (!freeze_task(task
))
286 if (is_task_frozen_enough(task
))
288 if (!freezing(task
) && !freezer_should_skip(task
))
289 num_cant_freeze_now
++;
291 cgroup_iter_end(cgroup
, &it
);
293 return num_cant_freeze_now
? -EBUSY
: 0;
296 static void unfreeze_cgroup(struct cgroup
*cgroup
, struct freezer
*freezer
)
298 struct cgroup_iter it
;
299 struct task_struct
*task
;
301 cgroup_iter_start(cgroup
, &it
);
302 while ((task
= cgroup_iter_next(cgroup
, &it
)))
304 cgroup_iter_end(cgroup
, &it
);
307 static int freezer_change_state(struct cgroup
*cgroup
,
308 enum freezer_state goal_state
)
310 struct freezer
*freezer
;
313 freezer
= cgroup_freezer(cgroup
);
315 spin_lock_irq(&freezer
->lock
);
317 update_if_frozen(cgroup
, freezer
);
319 switch (goal_state
) {
321 if (freezer
->state
!= CGROUP_THAWED
)
322 atomic_dec(&system_freezing_cnt
);
323 freezer
->state
= CGROUP_THAWED
;
324 unfreeze_cgroup(cgroup
, freezer
);
327 if (freezer
->state
== CGROUP_THAWED
)
328 atomic_inc(&system_freezing_cnt
);
329 freezer
->state
= CGROUP_FREEZING
;
330 retval
= try_to_freeze_cgroup(cgroup
, freezer
);
336 spin_unlock_irq(&freezer
->lock
);
341 static int freezer_write(struct cgroup
*cgroup
,
346 enum freezer_state goal_state
;
348 if (strcmp(buffer
, freezer_state_strs
[CGROUP_THAWED
]) == 0)
349 goal_state
= CGROUP_THAWED
;
350 else if (strcmp(buffer
, freezer_state_strs
[CGROUP_FROZEN
]) == 0)
351 goal_state
= CGROUP_FROZEN
;
355 if (!cgroup_lock_live_group(cgroup
))
357 retval
= freezer_change_state(cgroup
, goal_state
);
362 static struct cftype files
[] = {
365 .read_seq_string
= freezer_read
,
366 .write_string
= freezer_write
,
370 static int freezer_populate(struct cgroup_subsys
*ss
, struct cgroup
*cgroup
)
374 return cgroup_add_files(cgroup
, ss
, files
, ARRAY_SIZE(files
));
377 struct cgroup_subsys freezer_subsys
= {
379 .create
= freezer_create
,
380 .destroy
= freezer_destroy
,
381 .populate
= freezer_populate
,
382 .subsys_id
= freezer_subsys_id
,
383 .can_attach
= freezer_can_attach
,
384 .can_attach_task
= freezer_can_attach_task
,
388 .fork
= freezer_fork
,