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