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 * We change from FREEZING to FROZEN lazily if the cgroup was only
217 * partially frozen when we exitted write. Caller must hold freezer->lock.
219 * Task states and freezer state might disagree while tasks are being
220 * migrated into @cgroup, so we can't verify task states against @freezer
221 * state here. See freezer_attach() for details.
223 static void update_if_frozen(struct cgroup
*cgroup
, struct freezer
*freezer
)
225 struct cgroup_iter it
;
226 struct task_struct
*task
;
228 if (freezer
->state
!= CGROUP_FREEZING
)
231 cgroup_iter_start(cgroup
, &it
);
233 while ((task
= cgroup_iter_next(cgroup
, &it
))) {
234 if (freezing(task
)) {
236 * freezer_should_skip() indicates that the task
237 * should be skipped when determining freezing
238 * completion. Consider it frozen in addition to
239 * the usual frozen condition.
241 if (!frozen(task
) && !task_is_stopped_or_traced(task
) &&
242 !freezer_should_skip(task
))
247 freezer
->state
= CGROUP_FROZEN
;
249 cgroup_iter_end(cgroup
, &it
);
252 static int freezer_read(struct cgroup
*cgroup
, struct cftype
*cft
,
255 struct freezer
*freezer
;
256 enum freezer_state state
;
258 if (!cgroup_lock_live_group(cgroup
))
261 freezer
= cgroup_freezer(cgroup
);
262 spin_lock_irq(&freezer
->lock
);
263 update_if_frozen(cgroup
, freezer
);
264 state
= freezer
->state
;
265 spin_unlock_irq(&freezer
->lock
);
268 seq_puts(m
, freezer_state_strs
[state
]);
273 static void freeze_cgroup(struct cgroup
*cgroup
, struct freezer
*freezer
)
275 struct cgroup_iter it
;
276 struct task_struct
*task
;
278 cgroup_iter_start(cgroup
, &it
);
279 while ((task
= cgroup_iter_next(cgroup
, &it
)))
281 cgroup_iter_end(cgroup
, &it
);
284 static void unfreeze_cgroup(struct cgroup
*cgroup
, struct freezer
*freezer
)
286 struct cgroup_iter it
;
287 struct task_struct
*task
;
289 cgroup_iter_start(cgroup
, &it
);
290 while ((task
= cgroup_iter_next(cgroup
, &it
)))
292 cgroup_iter_end(cgroup
, &it
);
295 static void freezer_change_state(struct cgroup
*cgroup
,
296 enum freezer_state goal_state
)
298 struct freezer
*freezer
= cgroup_freezer(cgroup
);
300 spin_lock_irq(&freezer
->lock
);
302 switch (goal_state
) {
304 if (freezer
->state
!= CGROUP_THAWED
)
305 atomic_dec(&system_freezing_cnt
);
306 freezer
->state
= CGROUP_THAWED
;
307 unfreeze_cgroup(cgroup
, freezer
);
310 if (freezer
->state
== CGROUP_THAWED
)
311 atomic_inc(&system_freezing_cnt
);
312 freezer
->state
= CGROUP_FREEZING
;
313 freeze_cgroup(cgroup
, freezer
);
319 spin_unlock_irq(&freezer
->lock
);
322 static int freezer_write(struct cgroup
*cgroup
,
326 enum freezer_state goal_state
;
328 if (strcmp(buffer
, freezer_state_strs
[CGROUP_THAWED
]) == 0)
329 goal_state
= CGROUP_THAWED
;
330 else if (strcmp(buffer
, freezer_state_strs
[CGROUP_FROZEN
]) == 0)
331 goal_state
= CGROUP_FROZEN
;
335 if (!cgroup_lock_live_group(cgroup
))
337 freezer_change_state(cgroup
, goal_state
);
342 static struct cftype files
[] = {
345 .flags
= CFTYPE_NOT_ON_ROOT
,
346 .read_seq_string
= freezer_read
,
347 .write_string
= freezer_write
,
352 struct cgroup_subsys freezer_subsys
= {
354 .create
= freezer_create
,
355 .destroy
= freezer_destroy
,
356 .subsys_id
= freezer_subsys_id
,
357 .attach
= freezer_attach
,
358 .fork
= freezer_fork
,
359 .base_cftypes
= files
,
362 * freezer subsys doesn't handle hierarchy at all. Frozen state
363 * should be inherited through the hierarchy - if a parent is
364 * frozen, all its children should be frozen. Fix it and remove
367 .broken_hierarchy
= true,