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_flags {
  26         CGROUP_FREEZING         = (1 << 1), /* this freezer is freezing */
  27         CGROUP_FROZEN           = (1 << 3), /* this and its descendants frozen */
  28 };
  29
  30 struct freezer {
  31         struct cgroup_subsys_state      css;
  32         unsigned int                    state;
  33         spinlock_t                      lock;
  34 };
  35
  36 static inline struct freezer *cgroup_freezer(struct cgroup *cgroup)
  37 {
  38         return container_of(cgroup_subsys_state(cgroup, freezer_subsys_id),
  39                             struct freezer, css);
  40 }
  41
  42 static inline struct freezer *task_freezer(struct task_struct *task)
  43 {
  44         return container_of(task_subsys_state(task, freezer_subsys_id),
  45                             struct freezer, css);
  46 }
  47
  48 bool cgroup_freezing(struct task_struct *task)
  49 {
  50         bool ret;
  51
  52         rcu_read_lock();
  53         ret = task_freezer(task)->state & CGROUP_FREEZING;
  54         rcu_read_unlock();
  55
  56         return ret;
  57 }
  58
  59 /*
  60  * cgroups_write_string() limits the size of freezer state strings to
  61  * CGROUP_LOCAL_BUFFER_SIZE
  62  */
  63 static const char *freezer_state_strs(unsigned int state)
  64 {
  65         if (state & CGROUP_FROZEN)
  66                 return "FROZEN";
  67         if (state & CGROUP_FREEZING)
  68                 return "FREEZING";
  69         return "THAWED";
  70 };
  71
  72 /*
  73  * State diagram
  74  * Transitions are caused by userspace writes to the freezer.state file.
  75  * The values in parenthesis are state labels. The rest are edge labels.
  76  *
  77  * (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
  78  *    ^ ^                    |                     |
  79  *    | \_______THAWED_______/                     |
  80  *    \__________________________THAWED____________/
  81  */
  82
  83 struct cgroup_subsys freezer_subsys;
  84
  85 static struct cgroup_subsys_state *freezer_create(struct cgroup *cgroup)
  86 {
  87         struct freezer *freezer;
  88
  89         freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
  90         if (!freezer)
  91                 return ERR_PTR(-ENOMEM);
  92
  93         spin_lock_init(&freezer->lock);
  94         return &freezer->css;
  95 }
  96
  97 static void freezer_destroy(struct cgroup *cgroup)
  98 {
  99         struct freezer *freezer = cgroup_freezer(cgroup);
 100
 101         if (freezer->state & CGROUP_FREEZING)
 102                 atomic_dec(&system_freezing_cnt);
 103         kfree(freezer);
 104 }
 105
 106 /*
 107  * Tasks can be migrated into a different freezer anytime regardless of its
 108  * current state.  freezer_attach() is responsible for making new tasks
 109  * conform to the current state.
 110  *
 111  * Freezer state changes and task migration are synchronized via
 112  * @freezer->lock.  freezer_attach() makes the new tasks conform to the
 113  * current state and all following state changes can see the new tasks.
 114  */
 115 static void freezer_attach(struct cgroup *new_cgrp, struct cgroup_taskset *tset)
 116 {
 117         struct freezer *freezer = cgroup_freezer(new_cgrp);
 118         struct task_struct *task;
 119
 120         spin_lock_irq(&freezer->lock);
 121
 122         /*
 123          * Make the new tasks conform to the current state of @new_cgrp.
 124          * For simplicity, when migrating any task to a FROZEN cgroup, we
 125          * revert it to FREEZING and let update_if_frozen() determine the
 126          * correct state later.
 127          *
 128          * Tasks in @tset are on @new_cgrp but may not conform to its
 129          * current state before executing the following - !frozen tasks may
 130          * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
 131          */
 132         cgroup_taskset_for_each(task, new_cgrp, tset) {
 133                 if (!(freezer->state & CGROUP_FREEZING)) {
 134                         __thaw_task(task);
 135                 } else {
 136                         freeze_task(task);
 137                         freezer->state &= ~CGROUP_FROZEN;
 138                 }
 139         }
 140
 141         spin_unlock_irq(&freezer->lock);
 142 }
 143
 144 static void freezer_fork(struct task_struct *task)
 145 {
 146         struct freezer *freezer;
 147
 148         rcu_read_lock();
 149         freezer = task_freezer(task);
 150
 151         /*
 152          * The root cgroup is non-freezable, so we can skip the
 153          * following check.
 154          */
 155         if (!freezer->css.cgroup->parent)
 156                 goto out;
 157
 158         spin_lock_irq(&freezer->lock);
 159         if (freezer->state & CGROUP_FREEZING)
 160                 freeze_task(task);
 161         spin_unlock_irq(&freezer->lock);
 162 out:
 163         rcu_read_unlock();
 164 }
 165
 166 /*
 167  * We change from FREEZING to FROZEN lazily if the cgroup was only
 168  * partially frozen when we exitted write.  Caller must hold freezer->lock.
 169  *
 170  * Task states and freezer state might disagree while tasks are being
 171  * migrated into or out of @cgroup, so we can't verify task states against
 172  * @freezer state here.  See freezer_attach() for details.
 173  */
 174 static void update_if_frozen(struct freezer *freezer)
 175 {
 176         struct cgroup *cgroup = freezer->css.cgroup;
 177         struct cgroup_iter it;
 178         struct task_struct *task;
 179
 180         if (!(freezer->state & CGROUP_FREEZING) ||
 181             (freezer->state & CGROUP_FROZEN))
 182                 return;
 183
 184         cgroup_iter_start(cgroup, &it);
 185
 186         while ((task = cgroup_iter_next(cgroup, &it))) {
 187                 if (freezing(task)) {
 188                         /*
 189                          * freezer_should_skip() indicates that the task
 190                          * should be skipped when determining freezing
 191                          * completion.  Consider it frozen in addition to
 192                          * the usual frozen condition.
 193                          */
 194                         if (!frozen(task) && !freezer_should_skip(task))
 195                                 goto notyet;
 196                 }
 197         }
 198
 199         freezer->state |= CGROUP_FROZEN;
 200 notyet:
 201         cgroup_iter_end(cgroup, &it);
 202 }
 203
 204 static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
 205                         struct seq_file *m)
 206 {
 207         struct freezer *freezer = cgroup_freezer(cgroup);
 208         unsigned int state;
 209
 210         spin_lock_irq(&freezer->lock);
 211         update_if_frozen(freezer);
 212         state = freezer->state;
 213         spin_unlock_irq(&freezer->lock);
 214
 215         seq_puts(m, freezer_state_strs(state));
 216         seq_putc(m, '\n');
 217         return 0;
 218 }
 219
 220 static void freeze_cgroup(struct freezer *freezer)
 221 {
 222         struct cgroup *cgroup = freezer->css.cgroup;
 223         struct cgroup_iter it;
 224         struct task_struct *task;
 225
 226         cgroup_iter_start(cgroup, &it);
 227         while ((task = cgroup_iter_next(cgroup, &it)))
 228                 freeze_task(task);
 229         cgroup_iter_end(cgroup, &it);
 230 }
 231
 232 static void unfreeze_cgroup(struct freezer *freezer)
 233 {
 234         struct cgroup *cgroup = freezer->css.cgroup;
 235         struct cgroup_iter it;
 236         struct task_struct *task;
 237
 238         cgroup_iter_start(cgroup, &it);
 239         while ((task = cgroup_iter_next(cgroup, &it)))
 240                 __thaw_task(task);
 241         cgroup_iter_end(cgroup, &it);
 242 }
 243
 244 /**
 245  * freezer_apply_state - apply state change to a single cgroup_freezer
 246  * @freezer: freezer to apply state change to
 247  * @freeze: whether to freeze or unfreeze
 248  */
 249 static void freezer_apply_state(struct freezer *freezer, bool freeze)
 250 {
 251         /* also synchronizes against task migration, see freezer_attach() */
 252         lockdep_assert_held(&freezer->lock);
 253
 254         if (freeze) {
 255                 if (!(freezer->state & CGROUP_FREEZING))
 256                         atomic_inc(&system_freezing_cnt);
 257                 freezer->state |= CGROUP_FREEZING;
 258                 freeze_cgroup(freezer);
 259         } else {
 260                 if (freezer->state & CGROUP_FREEZING)
 261                         atomic_dec(&system_freezing_cnt);
 262                 freezer->state &= ~(CGROUP_FREEZING | CGROUP_FROZEN);
 263                 unfreeze_cgroup(freezer);
 264         }
 265 }
 266
 267 /**
 268  * freezer_change_state - change the freezing state of a cgroup_freezer
 269  * @freezer: freezer of interest
 270  * @freeze: whether to freeze or thaw
 271  *
 272  * Freeze or thaw @cgroup according to @freeze.
 273  */
 274 static void freezer_change_state(struct freezer *freezer, bool freeze)
 275 {
 276         /* update @freezer */
 277         spin_lock_irq(&freezer->lock);
 278         freezer_apply_state(freezer, freeze);
 279         spin_unlock_irq(&freezer->lock);
 280 }
 281
 282 static int freezer_write(struct cgroup *cgroup, struct cftype *cft,
 283                          const char *buffer)
 284 {
 285         bool freeze;
 286
 287         if (strcmp(buffer, freezer_state_strs(0)) == 0)
 288                 freeze = false;
 289         else if (strcmp(buffer, freezer_state_strs(CGROUP_FROZEN)) == 0)
 290                 freeze = true;
 291         else
 292                 return -EINVAL;
 293
 294         freezer_change_state(cgroup_freezer(cgroup), freeze);
 295         return 0;
 296 }
 297
 298 static struct cftype files[] = {
 299         {
 300                 .name = "state",
 301                 .flags = CFTYPE_NOT_ON_ROOT,
 302                 .read_seq_string = freezer_read,
 303                 .write_string = freezer_write,
 304         },
 305         { }     /* terminate */
 306 };
 307
 308 struct cgroup_subsys freezer_subsys = {
 309         .name           = "freezer",
 310         .create         = freezer_create,
 311         .destroy        = freezer_destroy,
 312         .subsys_id      = freezer_subsys_id,
 313         .attach         = freezer_attach,
 314         .fork           = freezer_fork,
 315         .base_cftypes   = files,
 316
 317         /*
 318          * freezer subsys doesn't handle hierarchy at all.  Frozen state
 319          * should be inherited through the hierarchy - if a parent is
 320          * frozen, all its children should be frozen.  Fix it and remove
 321          * the following.
 322          */
 323         .broken_hierarchy = true,
 324 };