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 enum freezer_state {
  26         CGROUP_THAWED = 0,
  27         CGROUP_FREEZING,
  28         CGROUP_FROZEN,
  29 };
  30
  31 struct freezer {
  32         struct cgroup_subsys_state css;
  33         enum freezer_state state;
  34         spinlock_t lock; /* protects _writes_ to state */
  35 };
  36
  37 static inline struct freezer *cgroup_freezer(
  38                 struct cgroup *cgroup)
  39 {
  40         return container_of(
  41                 cgroup_subsys_state(cgroup, freezer_subsys_id),
  42                 struct freezer, css);
  43 }
  44
  45 static inline struct freezer *task_freezer(struct task_struct *task)
  46 {
  47         return container_of(task_subsys_state(task, freezer_subsys_id),
  48                             struct freezer, css);
  49 }
  50
  51 bool cgroup_freezing(struct task_struct *task)
  52 {
  53         enum freezer_state state;
  54         bool ret;
  55
  56         rcu_read_lock();
  57         state = task_freezer(task)->state;
  58         ret = state == CGROUP_FREEZING || state == CGROUP_FROZEN;
  59         rcu_read_unlock();
  60
  61         return ret;
  62 }
  63
  64 /*
  65  * cgroups_write_string() limits the size of freezer state strings to
  66  * CGROUP_LOCAL_BUFFER_SIZE
  67  */
  68 static const char *freezer_state_strs[] = {
  69         "THAWED",
  70         "FREEZING",
  71         "FROZEN",
  72 };
  73
  74 /*
  75  * State diagram
  76  * Transitions are caused by userspace writes to the freezer.state file.
  77  * The values in parenthesis are state labels. The rest are edge labels.
  78  *
  79  * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
  80  *    ^ ^                    |                     |
  81  *    | \_______THAWED_______/                     |
  82  *    \__________________________THAWED____________/
  83  */
  84
  85 struct cgroup_subsys freezer_subsys;
  86
  87 static struct cgroup_subsys_state *freezer_create(struct cgroup *cgroup)
  88 {
  89         struct freezer *freezer;
  90
  91         freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
  92         if (!freezer)
  93                 return ERR_PTR(-ENOMEM);
  94
  95         spin_lock_init(&freezer->lock);
  96         freezer->state = CGROUP_THAWED;
  97         return &freezer->css;
  98 }
  99
 100 static void freezer_destroy(struct cgroup *cgroup)
 101 {
 102         struct freezer *freezer = cgroup_freezer(cgroup);
 103
 104         if (freezer->state != CGROUP_THAWED)
 105                 atomic_dec(&system_freezing_cnt);
 106         kfree(freezer);
 107 }
 108
 109 /*
 110  * Tasks can be migrated into a different freezer anytime regardless of its
 111  * current state.  freezer_attach() is responsible for making new tasks
 112  * conform to the current state.
 113  *
 114  * Freezer state changes and task migration are synchronized via
 115  * @freezer->lock.  freezer_attach() makes the new tasks conform to the
 116  * current state and all following state changes can see the new tasks.
 117  */
 118 static void freezer_attach(struct cgroup *new_cgrp, struct cgroup_taskset *tset)
 119 {
 120         struct freezer *freezer = cgroup_freezer(new_cgrp);
 121         struct task_struct *task;
 122
 123         spin_lock_irq(&freezer->lock);
 124
 125         /*
 126          * Make the new tasks conform to the current state of @new_cgrp.
 127          * For simplicity, when migrating any task to a FROZEN cgroup, we
 128          * revert it to FREEZING and let update_if_frozen() determine the
 129          * correct state later.
 130          *
 131          * Tasks in @tset are on @new_cgrp but may not conform to its
 132          * current state before executing the following - !frozen tasks may
 133          * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
 134          * This means that, to determine whether to freeze, one should test
 135          * whether the state equals THAWED.
 136          */
 137         cgroup_taskset_for_each(task, new_cgrp, tset) {
 138                 if (freezer->state == CGROUP_THAWED) {
 139                         __thaw_task(task);
 140                 } else {
 141                         freeze_task(task);
 142                         freezer->state = CGROUP_FREEZING;
 143                 }
 144         }
 145
 146         spin_unlock_irq(&freezer->lock);
 147 }
 148
 149 static void freezer_fork(struct task_struct *task)
 150 {
 151         struct freezer *freezer;
 152
 153         rcu_read_lock();
 154         freezer = task_freezer(task);
 155
 156         /*
 157          * The root cgroup is non-freezable, so we can skip the
 158          * following check.
 159          */
 160         if (!freezer->css.cgroup->parent)
 161                 goto out;
 162
 163         spin_lock_irq(&freezer->lock);
 164         /*
 165          * @task might have been just migrated into a FROZEN cgroup.  Test
 166          * equality with THAWED.  Read the comment in freezer_attach().
 167          */
 168         if (freezer->state != CGROUP_THAWED)
 169                 freeze_task(task);
 170         spin_unlock_irq(&freezer->lock);
 171 out:
 172         rcu_read_unlock();
 173 }
 174
 175 /*
 176  * We change from FREEZING to FROZEN lazily if the cgroup was only
 177  * partially frozen when we exitted write.  Caller must hold freezer->lock.
 178  *
 179  * Task states and freezer state might disagree while tasks are being
 180  * migrated into or out of @cgroup, so we can't verify task states against
 181  * @freezer state here.  See freezer_attach() for details.
 182  */
 183 static void update_if_frozen(struct cgroup *cgroup, struct freezer *freezer)
 184 {
 185         struct cgroup_iter it;
 186         struct task_struct *task;
 187
 188         if (freezer->state != CGROUP_FREEZING)
 189                 return;
 190
 191         cgroup_iter_start(cgroup, &it);
 192
 193         while ((task = cgroup_iter_next(cgroup, &it))) {
 194                 if (freezing(task)) {
 195                         /*
 196                          * freezer_should_skip() indicates that the task
 197                          * should be skipped when determining freezing
 198                          * completion.  Consider it frozen in addition to
 199                          * the usual frozen condition.
 200                          */
 201                         if (!frozen(task) && !freezer_should_skip(task))
 202                                 goto notyet;
 203                 }
 204         }
 205
 206         freezer->state = CGROUP_FROZEN;
 207 notyet:
 208         cgroup_iter_end(cgroup, &it);
 209 }
 210
 211 static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
 212                         struct seq_file *m)
 213 {
 214         struct freezer *freezer;
 215         enum freezer_state state;
 216
 217         freezer = cgroup_freezer(cgroup);
 218         spin_lock_irq(&freezer->lock);
 219         update_if_frozen(cgroup, freezer);
 220         state = freezer->state;
 221         spin_unlock_irq(&freezer->lock);
 222
 223         seq_puts(m, freezer_state_strs[state]);
 224         seq_putc(m, '\n');
 225         return 0;
 226 }
 227
 228 static void freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
 229 {
 230         struct cgroup_iter it;
 231         struct task_struct *task;
 232
 233         cgroup_iter_start(cgroup, &it);
 234         while ((task = cgroup_iter_next(cgroup, &it)))
 235                 freeze_task(task);
 236         cgroup_iter_end(cgroup, &it);
 237 }
 238
 239 static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
 240 {
 241         struct cgroup_iter it;
 242         struct task_struct *task;
 243
 244         cgroup_iter_start(cgroup, &it);
 245         while ((task = cgroup_iter_next(cgroup, &it)))
 246                 __thaw_task(task);
 247         cgroup_iter_end(cgroup, &it);
 248 }
 249
 250 static void freezer_change_state(struct cgroup *cgroup,
 251                                  enum freezer_state goal_state)
 252 {
 253         struct freezer *freezer = cgroup_freezer(cgroup);
 254
 255         /* also synchronizes against task migration, see freezer_attach() */
 256         spin_lock_irq(&freezer->lock);
 257
 258         switch (goal_state) {
 259         case CGROUP_THAWED:
 260                 if (freezer->state != CGROUP_THAWED)
 261                         atomic_dec(&system_freezing_cnt);
 262                 freezer->state = CGROUP_THAWED;
 263                 unfreeze_cgroup(cgroup, freezer);
 264                 break;
 265         case CGROUP_FROZEN:
 266                 if (freezer->state == CGROUP_THAWED)
 267                         atomic_inc(&system_freezing_cnt);
 268                 freezer->state = CGROUP_FREEZING;
 269                 freeze_cgroup(cgroup, freezer);
 270                 break;
 271         default:
 272                 BUG();
 273         }
 274
 275         spin_unlock_irq(&freezer->lock);
 276 }
 277
 278 static int freezer_write(struct cgroup *cgroup,
 279                          struct cftype *cft,
 280                          const char *buffer)
 281 {
 282         enum freezer_state goal_state;
 283
 284         if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
 285                 goal_state = CGROUP_THAWED;
 286         else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
 287                 goal_state = CGROUP_FROZEN;
 288         else
 289                 return -EINVAL;
 290
 291         freezer_change_state(cgroup, goal_state);
 292         return 0;
 293 }
 294
 295 static struct cftype files[] = {
 296         {
 297                 .name = "state",
 298                 .flags = CFTYPE_NOT_ON_ROOT,
 299                 .read_seq_string = freezer_read,
 300                 .write_string = freezer_write,
 301         },
 302         { }     /* terminate */
 303 };
 304
 305 struct cgroup_subsys freezer_subsys = {
 306         .name           = "freezer",
 307         .create         = freezer_create,
 308         .destroy        = freezer_destroy,
 309         .subsys_id      = freezer_subsys_id,
 310         .attach         = freezer_attach,
 311         .fork           = freezer_fork,
 312         .base_cftypes   = files,
 313
 314         /*
 315          * freezer subsys doesn't handle hierarchy at all.  Frozen state
 316          * should be inherited through the hierarchy - if a parent is
 317          * frozen, all its children should be frozen.  Fix it and remove
 318          * the following.
 319          */
 320         .broken_hierarchy = true,
 321 };