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