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  */
  33 enum 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
  43 struct freezer {
  44         struct cgroup_subsys_state      css;
  45         unsigned int                    state;
  46 };
  47
  48 static DEFINE_MUTEX(freezer_mutex);
  49
  50 static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
  51 {
  52         return css ? container_of(css, struct freezer, css) : NULL;
  53 }
  54
  55 static inline struct freezer *task_freezer(struct task_struct *task)
  56 {
  57         return css_freezer(task_css(task, freezer_cgrp_id));
  58 }
  59
  60 static struct freezer *parent_freezer(struct freezer *freezer)
  61 {
  62         return css_freezer(freezer->css.parent);
  63 }
  64
  65 bool 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 static 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
  85 static struct cgroup_subsys_state *
  86 freezer_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  */
 105 static 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  */
 130 static 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
 144 static 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  */
 158 static void freezer_attach(struct cgroup_subsys_state *new_css,
 159                            struct cgroup_taskset *tset)
 160 {
 161         struct freezer *freezer = css_freezer(new_css);
 162         struct task_struct *task;
 163         bool clear_frozen = false;
 164
 165         mutex_lock(&freezer_mutex);
 166
 167         /*
 168          * Make the new tasks conform to the current state of @new_css.
 169          * For simplicity, when migrating any task to a FROZEN cgroup, we
 170          * revert it to FREEZING and let update_if_frozen() determine the
 171          * correct state later.
 172          *
 173          * Tasks in @tset are on @new_css but may not conform to its
 174          * current state before executing the following - !frozen tasks may
 175          * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
 176          */
 177         cgroup_taskset_for_each(task, tset) {
 178                 if (!(freezer->state & CGROUP_FREEZING)) {
 179                         __thaw_task(task);
 180                 } else {
 181                         freeze_task(task);
 182                         freezer->state &= ~CGROUP_FROZEN;
 183                         clear_frozen = true;
 184                 }
 185         }
 186
 187         /* propagate FROZEN clearing upwards */
 188         while (clear_frozen && (freezer = parent_freezer(freezer))) {
 189                 freezer->state &= ~CGROUP_FROZEN;
 190                 clear_frozen = freezer->state & CGROUP_FREEZING;
 191         }
 192
 193         mutex_unlock(&freezer_mutex);
 194 }
 195
 196 /**
 197  * freezer_fork - cgroup post fork callback
 198  * @task: a task which has just been forked
 199  *
 200  * @task has just been created and should conform to the current state of
 201  * the cgroup_freezer it belongs to.  This function may race against
 202  * freezer_attach().  Losing to freezer_attach() means that we don't have
 203  * to do anything as freezer_attach() will put @task into the appropriate
 204  * state.
 205  */
 206 static void freezer_fork(struct task_struct *task)
 207 {
 208         struct freezer *freezer;
 209
 210         /*
 211          * The root cgroup is non-freezable, so we can skip locking the
 212          * freezer.  This is safe regardless of race with task migration.
 213          * If we didn't race or won, skipping is obviously the right thing
 214          * to do.  If we lost and root is the new cgroup, noop is still the
 215          * right thing to do.
 216          */
 217         if (task_css_is_root(task, freezer_cgrp_id))
 218                 return;
 219
 220         mutex_lock(&freezer_mutex);
 221         rcu_read_lock();
 222
 223         freezer = task_freezer(task);
 224         if (freezer->state & CGROUP_FREEZING)
 225                 freeze_task(task);
 226
 227         rcu_read_unlock();
 228         mutex_unlock(&freezer_mutex);
 229 }
 230
 231 /**
 232  * update_if_frozen - update whether a cgroup finished freezing
 233  * @css: css of interest
 234  *
 235  * Once FREEZING is initiated, transition to FROZEN is lazily updated by
 236  * calling this function.  If the current state is FREEZING but not FROZEN,
 237  * this function checks whether all tasks of this cgroup and the descendant
 238  * cgroups finished freezing and, if so, sets FROZEN.
 239  *
 240  * The caller is responsible for grabbing RCU read lock and calling
 241  * update_if_frozen() on all descendants prior to invoking this function.
 242  *
 243  * Task states and freezer state might disagree while tasks are being
 244  * migrated into or out of @css, so we can't verify task states against
 245  * @freezer state here.  See freezer_attach() for details.
 246  */
 247 static void update_if_frozen(struct cgroup_subsys_state *css)
 248 {
 249         struct freezer *freezer = css_freezer(css);
 250         struct cgroup_subsys_state *pos;
 251         struct css_task_iter it;
 252         struct task_struct *task;
 253
 254         lockdep_assert_held(&freezer_mutex);
 255
 256         if (!(freezer->state & CGROUP_FREEZING) ||
 257             (freezer->state & CGROUP_FROZEN))
 258                 return;
 259
 260         /* are all (live) children frozen? */
 261         rcu_read_lock();
 262         css_for_each_child(pos, css) {
 263                 struct freezer *child = css_freezer(pos);
 264
 265                 if ((child->state & CGROUP_FREEZER_ONLINE) &&
 266                     !(child->state & CGROUP_FROZEN)) {
 267                         rcu_read_unlock();
 268                         return;
 269                 }
 270         }
 271         rcu_read_unlock();
 272
 273         /* are all tasks frozen? */
 274         css_task_iter_start(css, &it);
 275
 276         while ((task = css_task_iter_next(&it))) {
 277                 if (freezing(task)) {
 278                         /*
 279                          * freezer_should_skip() indicates that the task
 280                          * should be skipped when determining freezing
 281                          * completion.  Consider it frozen in addition to
 282                          * the usual frozen condition.
 283                          */
 284                         if (!frozen(task) && !freezer_should_skip(task))
 285                                 goto out_iter_end;
 286                 }
 287         }
 288
 289         freezer->state |= CGROUP_FROZEN;
 290 out_iter_end:
 291         css_task_iter_end(&it);
 292 }
 293
 294 static int freezer_read(struct seq_file *m, void *v)
 295 {
 296         struct cgroup_subsys_state *css = seq_css(m), *pos;
 297
 298         mutex_lock(&freezer_mutex);
 299         rcu_read_lock();
 300
 301         /* update states bottom-up */
 302         css_for_each_descendant_post(pos, css) {
 303                 if (!css_tryget_online(pos))
 304                         continue;
 305                 rcu_read_unlock();
 306
 307                 update_if_frozen(pos);
 308
 309                 rcu_read_lock();
 310                 css_put(pos);
 311         }
 312
 313         rcu_read_unlock();
 314         mutex_unlock(&freezer_mutex);
 315
 316         seq_puts(m, freezer_state_strs(css_freezer(css)->state));
 317         seq_putc(m, '\n');
 318         return 0;
 319 }
 320
 321 static void freeze_cgroup(struct freezer *freezer)
 322 {
 323         struct css_task_iter it;
 324         struct task_struct *task;
 325
 326         css_task_iter_start(&freezer->css, &it);
 327         while ((task = css_task_iter_next(&it)))
 328                 freeze_task(task);
 329         css_task_iter_end(&it);
 330 }
 331
 332 static void unfreeze_cgroup(struct freezer *freezer)
 333 {
 334         struct css_task_iter it;
 335         struct task_struct *task;
 336
 337         css_task_iter_start(&freezer->css, &it);
 338         while ((task = css_task_iter_next(&it)))
 339                 __thaw_task(task);
 340         css_task_iter_end(&it);
 341 }
 342
 343 /**
 344  * freezer_apply_state - apply state change to a single cgroup_freezer
 345  * @freezer: freezer to apply state change to
 346  * @freeze: whether to freeze or unfreeze
 347  * @state: CGROUP_FREEZING_* flag to set or clear
 348  *
 349  * Set or clear @state on @cgroup according to @freeze, and perform
 350  * freezing or thawing as necessary.
 351  */
 352 static void freezer_apply_state(struct freezer *freezer, bool freeze,
 353                                 unsigned int state)
 354 {
 355         /* also synchronizes against task migration, see freezer_attach() */
 356         lockdep_assert_held(&freezer_mutex);
 357
 358         if (!(freezer->state & CGROUP_FREEZER_ONLINE))
 359                 return;
 360
 361         if (freeze) {
 362                 if (!(freezer->state & CGROUP_FREEZING))
 363                         atomic_inc(&system_freezing_cnt);
 364                 freezer->state |= state;
 365                 freeze_cgroup(freezer);
 366         } else {
 367                 bool was_freezing = freezer->state & CGROUP_FREEZING;
 368
 369                 freezer->state &= ~state;
 370
 371                 if (!(freezer->state & CGROUP_FREEZING)) {
 372                         if (was_freezing)
 373                                 atomic_dec(&system_freezing_cnt);
 374                         freezer->state &= ~CGROUP_FROZEN;
 375                         unfreeze_cgroup(freezer);
 376                 }
 377         }
 378 }
 379
 380 /**
 381  * freezer_change_state - change the freezing state of a cgroup_freezer
 382  * @freezer: freezer of interest
 383  * @freeze: whether to freeze or thaw
 384  *
 385  * Freeze or thaw @freezer according to @freeze.  The operations are
 386  * recursive - all descendants of @freezer will be affected.
 387  */
 388 static void freezer_change_state(struct freezer *freezer, bool freeze)
 389 {
 390         struct cgroup_subsys_state *pos;
 391
 392         /*
 393          * Update all its descendants in pre-order traversal.  Each
 394          * descendant will try to inherit its parent's FREEZING state as
 395          * CGROUP_FREEZING_PARENT.
 396          */
 397         mutex_lock(&freezer_mutex);
 398         rcu_read_lock();
 399         css_for_each_descendant_pre(pos, &freezer->css) {
 400                 struct freezer *pos_f = css_freezer(pos);
 401                 struct freezer *parent = parent_freezer(pos_f);
 402
 403                 if (!css_tryget_online(pos))
 404                         continue;
 405                 rcu_read_unlock();
 406
 407                 if (pos_f == freezer)
 408                         freezer_apply_state(pos_f, freeze,
 409                                             CGROUP_FREEZING_SELF);
 410                 else
 411                         freezer_apply_state(pos_f,
 412                                             parent->state & CGROUP_FREEZING,
 413                                             CGROUP_FREEZING_PARENT);
 414
 415                 rcu_read_lock();
 416                 css_put(pos);
 417         }
 418         rcu_read_unlock();
 419         mutex_unlock(&freezer_mutex);
 420 }
 421
 422 static ssize_t freezer_write(struct kernfs_open_file *of,
 423                              char *buf, size_t nbytes, loff_t off)
 424 {
 425         bool freeze;
 426
 427         buf = strstrip(buf);
 428
 429         if (strcmp(buf, freezer_state_strs(0)) == 0)
 430                 freeze = false;
 431         else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0)
 432                 freeze = true;
 433         else
 434                 return -EINVAL;
 435
 436         freezer_change_state(css_freezer(of_css(of)), freeze);
 437         return nbytes;
 438 }
 439
 440 static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
 441                                       struct cftype *cft)
 442 {
 443         struct freezer *freezer = css_freezer(css);
 444
 445         return (bool)(freezer->state & CGROUP_FREEZING_SELF);
 446 }
 447
 448 static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
 449                                         struct cftype *cft)
 450 {
 451         struct freezer *freezer = css_freezer(css);
 452
 453         return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
 454 }
 455
 456 static struct cftype files[] = {
 457         {
 458                 .name = "state",
 459                 .flags = CFTYPE_NOT_ON_ROOT,
 460                 .seq_show = freezer_read,
 461                 .write = freezer_write,
 462         },
 463         {
 464                 .name = "self_freezing",
 465                 .flags = CFTYPE_NOT_ON_ROOT,
 466                 .read_u64 = freezer_self_freezing_read,
 467         },
 468         {
 469                 .name = "parent_freezing",
 470                 .flags = CFTYPE_NOT_ON_ROOT,
 471                 .read_u64 = freezer_parent_freezing_read,
 472         },
 473         { }     /* terminate */
 474 };
 475
 476 struct cgroup_subsys freezer_cgrp_subsys = {
 477         .css_alloc      = freezer_css_alloc,
 478         .css_online     = freezer_css_online,
 479         .css_offline    = freezer_css_offline,
 480         .css_free       = freezer_css_free,
 481         .attach         = freezer_attach,
 482         .fork           = freezer_fork,
 483         .base_cftypes   = files,
 484 };