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(css_parent(&freezer->css));
  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 /*
  77  * cgroups_write_string() limits the size of freezer state strings to
  78  * CGROUP_LOCAL_BUFFER_SIZE
  79  */
  80 static 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
  89 static struct cgroup_subsys_state *
  90 freezer_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  */
 109 static 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  */
 134 static 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
 148 static 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  */
 162 static 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  */
 210 static 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  */
 251 static 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;
 294 out_iter_end:
 295         css_task_iter_end(&it);
 296 }
 297
 298 static 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
 325 static 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
 336 static 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  */
 356 static 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  */
 392 static 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
 426 static 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
 442 static 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
 450 static 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
 458 static 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
 478 struct 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 };