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 the
156 * can_attach() result will remain valid until the attach completes.
158 static int freezer_can_attach(struct cgroup
*new_cgroup
,
159 struct cgroup_taskset
*tset
)
161 struct freezer
*freezer
;
162 struct task_struct
*task
;
165 * Anything frozen can't move or be moved to/from.
167 cgroup_taskset_for_each(task
, new_cgroup
, tset
)
168 if (cgroup_freezing(task
))
171 freezer
= cgroup_freezer(new_cgroup
);
172 if (freezer
->state
!= CGROUP_THAWED
)
178 static void freezer_fork(struct task_struct
*task
)
180 struct freezer
*freezer
;
183 freezer
= task_freezer(task
);
186 * The root cgroup is non-freezable, so we can skip the
189 if (!freezer
->css
.cgroup
->parent
)
192 spin_lock_irq(&freezer
->lock
);
193 BUG_ON(freezer
->state
== CGROUP_FROZEN
);
195 /* Locking avoids race with FREEZING -> THAWED transitions. */
196 if (freezer
->state
== CGROUP_FREEZING
)
199 spin_unlock_irq(&freezer
->lock
);
205 * caller must hold freezer->lock
207 static void update_if_frozen(struct cgroup
*cgroup
,
208 struct freezer
*freezer
)
210 struct cgroup_iter it
;
211 struct task_struct
*task
;
212 unsigned int nfrozen
= 0, ntotal
= 0;
213 enum freezer_state old_state
= freezer
->state
;
215 cgroup_iter_start(cgroup
, &it
);
216 while ((task
= cgroup_iter_next(cgroup
, &it
))) {
218 if (freezing(task
) && (frozen(task
) ||
219 task_is_stopped_or_traced(task
)))
223 if (old_state
== CGROUP_THAWED
) {
225 } else if (old_state
== CGROUP_FREEZING
) {
226 if (nfrozen
== ntotal
)
227 freezer
->state
= CGROUP_FROZEN
;
228 } else { /* old_state == CGROUP_FROZEN */
229 BUG_ON(nfrozen
!= ntotal
);
232 cgroup_iter_end(cgroup
, &it
);
235 static int freezer_read(struct cgroup
*cgroup
, struct cftype
*cft
,
238 struct freezer
*freezer
;
239 enum freezer_state state
;
241 if (!cgroup_lock_live_group(cgroup
))
244 freezer
= cgroup_freezer(cgroup
);
245 spin_lock_irq(&freezer
->lock
);
246 state
= freezer
->state
;
247 if (state
== CGROUP_FREEZING
) {
248 /* We change from FREEZING to FROZEN lazily if the cgroup was
249 * only partially frozen when we exitted write. */
250 update_if_frozen(cgroup
, freezer
);
251 state
= freezer
->state
;
253 spin_unlock_irq(&freezer
->lock
);
256 seq_puts(m
, freezer_state_strs
[state
]);
261 static void freeze_cgroup(struct cgroup
*cgroup
, struct freezer
*freezer
)
263 struct cgroup_iter it
;
264 struct task_struct
*task
;
266 cgroup_iter_start(cgroup
, &it
);
267 while ((task
= cgroup_iter_next(cgroup
, &it
)))
269 cgroup_iter_end(cgroup
, &it
);
272 static void unfreeze_cgroup(struct cgroup
*cgroup
, struct freezer
*freezer
)
274 struct cgroup_iter it
;
275 struct task_struct
*task
;
277 cgroup_iter_start(cgroup
, &it
);
278 while ((task
= cgroup_iter_next(cgroup
, &it
)))
280 cgroup_iter_end(cgroup
, &it
);
283 static void freezer_change_state(struct cgroup
*cgroup
,
284 enum freezer_state goal_state
)
286 struct freezer
*freezer
= cgroup_freezer(cgroup
);
288 spin_lock_irq(&freezer
->lock
);
290 update_if_frozen(cgroup
, freezer
);
292 switch (goal_state
) {
294 if (freezer
->state
!= CGROUP_THAWED
)
295 atomic_dec(&system_freezing_cnt
);
296 freezer
->state
= CGROUP_THAWED
;
297 unfreeze_cgroup(cgroup
, freezer
);
300 if (freezer
->state
== CGROUP_THAWED
)
301 atomic_inc(&system_freezing_cnt
);
302 freezer
->state
= CGROUP_FREEZING
;
303 freeze_cgroup(cgroup
, freezer
);
309 spin_unlock_irq(&freezer
->lock
);
312 static int freezer_write(struct cgroup
*cgroup
,
316 enum freezer_state goal_state
;
318 if (strcmp(buffer
, freezer_state_strs
[CGROUP_THAWED
]) == 0)
319 goal_state
= CGROUP_THAWED
;
320 else if (strcmp(buffer
, freezer_state_strs
[CGROUP_FROZEN
]) == 0)
321 goal_state
= CGROUP_FROZEN
;
325 if (!cgroup_lock_live_group(cgroup
))
327 freezer_change_state(cgroup
, goal_state
);
332 static struct cftype files
[] = {
335 .flags
= CFTYPE_NOT_ON_ROOT
,
336 .read_seq_string
= freezer_read
,
337 .write_string
= freezer_write
,
342 struct cgroup_subsys freezer_subsys
= {
344 .create
= freezer_create
,
345 .destroy
= freezer_destroy
,
346 .subsys_id
= freezer_subsys_id
,
347 .can_attach
= freezer_can_attach
,
348 .fork
= freezer_fork
,
349 .base_cftypes
= files
,
352 * freezer subsys doesn't handle hierarchy at all. Frozen state
353 * should be inherited through the hierarchy - if a parent is
354 * frozen, all its children should be frozen. Fix it and remove
357 .broken_hierarchy
= true,