Root/kernel/cgroup_freezer.c

1/*
2 * cgroup_freezer.c - control group freezer subsystem
3 *
4 * Copyright IBM Corporation, 2007
5 *
6 * Author : Cedric Le Goater <clg@fr.ibm.com>
7 *
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.
11 *
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.
15 */
16
17#include <linux/export.h>
18#include <linux/slab.h>
19#include <linux/cgroup.h>
20#include <linux/fs.h>
21#include <linux/uaccess.h>
22#include <linux/freezer.h>
23#include <linux/seq_file.h>
24#include <linux/mutex.h>
25
26/*
27 * A cgroup is freezing if any FREEZING flags are set. FREEZING_SELF is
28 * set if "FROZEN" is written to freezer.state cgroupfs file, and cleared
29 * for "THAWED". FREEZING_PARENT is set if the parent freezer is FREEZING
30 * for whatever reason. IOW, a cgroup has FREEZING_PARENT set if one of
31 * its ancestors has FREEZING_SELF set.
32 */
33enum freezer_state_flags {
34    CGROUP_FREEZER_ONLINE = (1 << 0), /* freezer is fully online */
35    CGROUP_FREEZING_SELF = (1 << 1), /* this freezer is freezing */
36    CGROUP_FREEZING_PARENT = (1 << 2), /* the parent freezer is freezing */
37    CGROUP_FROZEN = (1 << 3), /* this and its descendants frozen */
38
39    /* mask for all FREEZING flags */
40    CGROUP_FREEZING = CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
41};
42
43struct freezer {
44    struct cgroup_subsys_state css;
45    unsigned int state;
46};
47
48static DEFINE_MUTEX(freezer_mutex);
49
50static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
51{
52    return css ? container_of(css, struct freezer, css) : NULL;
53}
54
55static inline struct freezer *task_freezer(struct task_struct *task)
56{
57    return css_freezer(task_css(task, freezer_cgrp_id));
58}
59
60static struct freezer *parent_freezer(struct freezer *freezer)
61{
62    return css_freezer(css_parent(&freezer->css));
63}
64
65bool cgroup_freezing(struct task_struct *task)
66{
67    bool ret;
68
69    rcu_read_lock();
70    ret = task_freezer(task)->state & CGROUP_FREEZING;
71    rcu_read_unlock();
72
73    return ret;
74}
75
76/*
77 * cgroups_write_string() limits the size of freezer state strings to
78 * CGROUP_LOCAL_BUFFER_SIZE
79 */
80static const char *freezer_state_strs(unsigned int state)
81{
82    if (state & CGROUP_FROZEN)
83        return "FROZEN";
84    if (state & CGROUP_FREEZING)
85        return "FREEZING";
86    return "THAWED";
87};
88
89static struct cgroup_subsys_state *
90freezer_css_alloc(struct cgroup_subsys_state *parent_css)
91{
92    struct freezer *freezer;
93
94    freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
95    if (!freezer)
96        return ERR_PTR(-ENOMEM);
97
98    return &freezer->css;
99}
100
101/**
102 * freezer_css_online - commit creation of a freezer css
103 * @css: css being created
104 *
105 * We're committing to creation of @css. Mark it online and inherit
106 * parent's freezing state while holding both parent's and our
107 * freezer->lock.
108 */
109static int freezer_css_online(struct cgroup_subsys_state *css)
110{
111    struct freezer *freezer = css_freezer(css);
112    struct freezer *parent = parent_freezer(freezer);
113
114    mutex_lock(&freezer_mutex);
115
116    freezer->state |= CGROUP_FREEZER_ONLINE;
117
118    if (parent && (parent->state & CGROUP_FREEZING)) {
119        freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
120        atomic_inc(&system_freezing_cnt);
121    }
122
123    mutex_unlock(&freezer_mutex);
124    return 0;
125}
126
127/**
128 * freezer_css_offline - initiate destruction of a freezer css
129 * @css: css being destroyed
130 *
131 * @css is going away. Mark it dead and decrement system_freezing_count if
132 * it was holding one.
133 */
134static void freezer_css_offline(struct cgroup_subsys_state *css)
135{
136    struct freezer *freezer = css_freezer(css);
137
138    mutex_lock(&freezer_mutex);
139
140    if (freezer->state & CGROUP_FREEZING)
141        atomic_dec(&system_freezing_cnt);
142
143    freezer->state = 0;
144
145    mutex_unlock(&freezer_mutex);
146}
147
148static void freezer_css_free(struct cgroup_subsys_state *css)
149{
150    kfree(css_freezer(css));
151}
152
153/*
154 * Tasks can be migrated into a different freezer anytime regardless of its
155 * current state. freezer_attach() is responsible for making new tasks
156 * conform to the current state.
157 *
158 * Freezer state changes and task migration are synchronized via
159 * @freezer->lock. freezer_attach() makes the new tasks conform to the
160 * current state and all following state changes can see the new tasks.
161 */
162static void freezer_attach(struct cgroup_subsys_state *new_css,
163               struct cgroup_taskset *tset)
164{
165    struct freezer *freezer = css_freezer(new_css);
166    struct task_struct *task;
167    bool clear_frozen = false;
168
169    mutex_lock(&freezer_mutex);
170
171    /*
172     * Make the new tasks conform to the current state of @new_css.
173     * For simplicity, when migrating any task to a FROZEN cgroup, we
174     * revert it to FREEZING and let update_if_frozen() determine the
175     * correct state later.
176     *
177     * Tasks in @tset are on @new_css but may not conform to its
178     * current state before executing the following - !frozen tasks may
179     * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
180     */
181    cgroup_taskset_for_each(task, tset) {
182        if (!(freezer->state & CGROUP_FREEZING)) {
183            __thaw_task(task);
184        } else {
185            freeze_task(task);
186            freezer->state &= ~CGROUP_FROZEN;
187            clear_frozen = true;
188        }
189    }
190
191    /* propagate FROZEN clearing upwards */
192    while (clear_frozen && (freezer = parent_freezer(freezer))) {
193        freezer->state &= ~CGROUP_FROZEN;
194        clear_frozen = freezer->state & CGROUP_FREEZING;
195    }
196
197    mutex_unlock(&freezer_mutex);
198}
199
200/**
201 * freezer_fork - cgroup post fork callback
202 * @task: a task which has just been forked
203 *
204 * @task has just been created and should conform to the current state of
205 * the cgroup_freezer it belongs to. This function may race against
206 * freezer_attach(). Losing to freezer_attach() means that we don't have
207 * to do anything as freezer_attach() will put @task into the appropriate
208 * state.
209 */
210static void freezer_fork(struct task_struct *task)
211{
212    struct freezer *freezer;
213
214    /*
215     * The root cgroup is non-freezable, so we can skip locking the
216     * freezer. This is safe regardless of race with task migration.
217     * If we didn't race or won, skipping is obviously the right thing
218     * to do. If we lost and root is the new cgroup, noop is still the
219     * right thing to do.
220     */
221    if (task_css_is_root(task, freezer_cgrp_id))
222        return;
223
224    mutex_lock(&freezer_mutex);
225    rcu_read_lock();
226
227    freezer = task_freezer(task);
228    if (freezer->state & CGROUP_FREEZING)
229        freeze_task(task);
230
231    rcu_read_unlock();
232    mutex_unlock(&freezer_mutex);
233}
234
235/**
236 * update_if_frozen - update whether a cgroup finished freezing
237 * @css: css of interest
238 *
239 * Once FREEZING is initiated, transition to FROZEN is lazily updated by
240 * calling this function. If the current state is FREEZING but not FROZEN,
241 * this function checks whether all tasks of this cgroup and the descendant
242 * cgroups finished freezing and, if so, sets FROZEN.
243 *
244 * The caller is responsible for grabbing RCU read lock and calling
245 * update_if_frozen() on all descendants prior to invoking this function.
246 *
247 * Task states and freezer state might disagree while tasks are being
248 * migrated into or out of @css, so we can't verify task states against
249 * @freezer state here. See freezer_attach() for details.
250 */
251static void update_if_frozen(struct cgroup_subsys_state *css)
252{
253    struct freezer *freezer = css_freezer(css);
254    struct cgroup_subsys_state *pos;
255    struct css_task_iter it;
256    struct task_struct *task;
257
258    lockdep_assert_held(&freezer_mutex);
259
260    if (!(freezer->state & CGROUP_FREEZING) ||
261        (freezer->state & CGROUP_FROZEN))
262        return;
263
264    /* are all (live) children frozen? */
265    rcu_read_lock();
266    css_for_each_child(pos, css) {
267        struct freezer *child = css_freezer(pos);
268
269        if ((child->state & CGROUP_FREEZER_ONLINE) &&
270            !(child->state & CGROUP_FROZEN)) {
271            rcu_read_unlock();
272            return;
273        }
274    }
275    rcu_read_unlock();
276
277    /* are all tasks frozen? */
278    css_task_iter_start(css, &it);
279
280    while ((task = css_task_iter_next(&it))) {
281        if (freezing(task)) {
282            /*
283             * freezer_should_skip() indicates that the task
284             * should be skipped when determining freezing
285             * completion. Consider it frozen in addition to
286             * the usual frozen condition.
287             */
288            if (!frozen(task) && !freezer_should_skip(task))
289                goto out_iter_end;
290        }
291    }
292
293    freezer->state |= CGROUP_FROZEN;
294out_iter_end:
295    css_task_iter_end(&it);
296}
297
298static int freezer_read(struct seq_file *m, void *v)
299{
300    struct cgroup_subsys_state *css = seq_css(m), *pos;
301
302    mutex_lock(&freezer_mutex);
303    rcu_read_lock();
304
305    /* update states bottom-up */
306    css_for_each_descendant_post(pos, css) {
307        if (!css_tryget(pos))
308            continue;
309        rcu_read_unlock();
310
311        update_if_frozen(pos);
312
313        rcu_read_lock();
314        css_put(pos);
315    }
316
317    rcu_read_unlock();
318    mutex_unlock(&freezer_mutex);
319
320    seq_puts(m, freezer_state_strs(css_freezer(css)->state));
321    seq_putc(m, '\n');
322    return 0;
323}
324
325static void freeze_cgroup(struct freezer *freezer)
326{
327    struct css_task_iter it;
328    struct task_struct *task;
329
330    css_task_iter_start(&freezer->css, &it);
331    while ((task = css_task_iter_next(&it)))
332        freeze_task(task);
333    css_task_iter_end(&it);
334}
335
336static void unfreeze_cgroup(struct freezer *freezer)
337{
338    struct css_task_iter it;
339    struct task_struct *task;
340
341    css_task_iter_start(&freezer->css, &it);
342    while ((task = css_task_iter_next(&it)))
343        __thaw_task(task);
344    css_task_iter_end(&it);
345}
346
347/**
348 * freezer_apply_state - apply state change to a single cgroup_freezer
349 * @freezer: freezer to apply state change to
350 * @freeze: whether to freeze or unfreeze
351 * @state: CGROUP_FREEZING_* flag to set or clear
352 *
353 * Set or clear @state on @cgroup according to @freeze, and perform
354 * freezing or thawing as necessary.
355 */
356static void freezer_apply_state(struct freezer *freezer, bool freeze,
357                unsigned int state)
358{
359    /* also synchronizes against task migration, see freezer_attach() */
360    lockdep_assert_held(&freezer_mutex);
361
362    if (!(freezer->state & CGROUP_FREEZER_ONLINE))
363        return;
364
365    if (freeze) {
366        if (!(freezer->state & CGROUP_FREEZING))
367            atomic_inc(&system_freezing_cnt);
368        freezer->state |= state;
369        freeze_cgroup(freezer);
370    } else {
371        bool was_freezing = freezer->state & CGROUP_FREEZING;
372
373        freezer->state &= ~state;
374
375        if (!(freezer->state & CGROUP_FREEZING)) {
376            if (was_freezing)
377                atomic_dec(&system_freezing_cnt);
378            freezer->state &= ~CGROUP_FROZEN;
379            unfreeze_cgroup(freezer);
380        }
381    }
382}
383
384/**
385 * freezer_change_state - change the freezing state of a cgroup_freezer
386 * @freezer: freezer of interest
387 * @freeze: whether to freeze or thaw
388 *
389 * Freeze or thaw @freezer according to @freeze. The operations are
390 * recursive - all descendants of @freezer will be affected.
391 */
392static void freezer_change_state(struct freezer *freezer, bool freeze)
393{
394    struct cgroup_subsys_state *pos;
395
396    /*
397     * Update all its descendants in pre-order traversal. Each
398     * descendant will try to inherit its parent's FREEZING state as
399     * CGROUP_FREEZING_PARENT.
400     */
401    mutex_lock(&freezer_mutex);
402    rcu_read_lock();
403    css_for_each_descendant_pre(pos, &freezer->css) {
404        struct freezer *pos_f = css_freezer(pos);
405        struct freezer *parent = parent_freezer(pos_f);
406
407        if (!css_tryget(pos))
408            continue;
409        rcu_read_unlock();
410
411        if (pos_f == freezer)
412            freezer_apply_state(pos_f, freeze,
413                        CGROUP_FREEZING_SELF);
414        else
415            freezer_apply_state(pos_f,
416                        parent->state & CGROUP_FREEZING,
417                        CGROUP_FREEZING_PARENT);
418
419        rcu_read_lock();
420        css_put(pos);
421    }
422    rcu_read_unlock();
423    mutex_unlock(&freezer_mutex);
424}
425
426static int freezer_write(struct cgroup_subsys_state *css, struct cftype *cft,
427             char *buffer)
428{
429    bool freeze;
430
431    if (strcmp(buffer, freezer_state_strs(0)) == 0)
432        freeze = false;
433    else if (strcmp(buffer, freezer_state_strs(CGROUP_FROZEN)) == 0)
434        freeze = true;
435    else
436        return -EINVAL;
437
438    freezer_change_state(css_freezer(css), freeze);
439    return 0;
440}
441
442static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
443                      struct cftype *cft)
444{
445    struct freezer *freezer = css_freezer(css);
446
447    return (bool)(freezer->state & CGROUP_FREEZING_SELF);
448}
449
450static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
451                    struct cftype *cft)
452{
453    struct freezer *freezer = css_freezer(css);
454
455    return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
456}
457
458static struct cftype files[] = {
459    {
460        .name = "state",
461        .flags = CFTYPE_NOT_ON_ROOT,
462        .seq_show = freezer_read,
463        .write_string = freezer_write,
464    },
465    {
466        .name = "self_freezing",
467        .flags = CFTYPE_NOT_ON_ROOT,
468        .read_u64 = freezer_self_freezing_read,
469    },
470    {
471        .name = "parent_freezing",
472        .flags = CFTYPE_NOT_ON_ROOT,
473        .read_u64 = freezer_parent_freezing_read,
474    },
475    { } /* terminate */
476};
477
478struct cgroup_subsys freezer_cgrp_subsys = {
479    .css_alloc = freezer_css_alloc,
480    .css_online = freezer_css_online,
481    .css_offline = freezer_css_offline,
482    .css_free = freezer_css_free,
483    .attach = freezer_attach,
484    .fork = freezer_fork,
485    .base_cftypes = files,
486};
487

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