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 /* Locks taken and their ordering
  88  * ------------------------------
  89  * cgroup_mutex (AKA cgroup_lock)
  90  * freezer->lock
  91  * css_set_lock
  92  * task->alloc_lock (AKA task_lock)
  93  * task->sighand->siglock
  94  *
  95  * cgroup code forces css_set_lock to be taken before task->alloc_lock
  96  *
  97  * freezer_create(), freezer_destroy():
  98  * cgroup_mutex [ by cgroup core ]
  99  *
 100  * freezer_can_attach():
 101  * cgroup_mutex (held by caller of can_attach)
 102  *
 103  * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
 104  * freezer->lock
 105  *  sighand->siglock (if the cgroup is freezing)
 106  *
 107  * freezer_read():
 108  * cgroup_mutex
 109  *  freezer->lock
 110  *   write_lock css_set_lock (cgroup iterator start)
 111  *    task->alloc_lock
 112  *   read_lock css_set_lock (cgroup iterator start)
 113  *
 114  * freezer_write() (freeze):
 115  * cgroup_mutex
 116  *  freezer->lock
 117  *   write_lock css_set_lock (cgroup iterator start)
 118  *    task->alloc_lock
 119  *   read_lock css_set_lock (cgroup iterator start)
 120  *    sighand->siglock (fake signal delivery inside freeze_task())
 121  *
 122  * freezer_write() (unfreeze):
 123  * cgroup_mutex
 124  *  freezer->lock
 125  *   write_lock css_set_lock (cgroup iterator start)
 126  *    task->alloc_lock
 127  *   read_lock css_set_lock (cgroup iterator start)
 128  *    task->alloc_lock (inside __thaw_task(), prevents race with refrigerator())
 129  *     sighand->siglock
 130  */
 131 static struct cgroup_subsys_state *freezer_create(struct cgroup *cgroup)
 132 {
 133         struct freezer *freezer;
 134
 135         freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
 136         if (!freezer)
 137                 return ERR_PTR(-ENOMEM);
 138
 139         spin_lock_init(&freezer->lock);
 140         freezer->state = CGROUP_THAWED;
 141         return &freezer->css;
 142 }
 143
 144 static void freezer_destroy(struct cgroup *cgroup)
 145 {
 146         struct freezer *freezer = cgroup_freezer(cgroup);
 147
 148         if (freezer->state != CGROUP_THAWED)
 149                 atomic_dec(&system_freezing_cnt);
 150         kfree(freezer);
 151 }
 152
 153 /*
 154  * The call to cgroup_lock() in the freezer.state write method prevents
 155  * a write to that file racing against an attach, and hence the
 156  * can_attach() result will remain valid until the attach completes.
 157  */
 158 static int freezer_can_attach(struct cgroup *new_cgroup,
 159                               struct cgroup_taskset *tset)
 160 {
 161         struct freezer *freezer;
 162         struct task_struct *task;
 163
 164         /*
 165          * Anything frozen can't move or be moved to/from.
 166          */
 167         cgroup_taskset_for_each(task, new_cgroup, tset)
 168                 if (cgroup_freezing(task))
 169                         return -EBUSY;
 170
 171         freezer = cgroup_freezer(new_cgroup);
 172         if (freezer->state != CGROUP_THAWED)
 173                 return -EBUSY;
 174
 175         return 0;
 176 }
 177
 178 static void freezer_fork(struct task_struct *task)
 179 {
 180         struct freezer *freezer;
 181
 182         rcu_read_lock();
 183         freezer = task_freezer(task);
 184
 185         /*
 186          * The root cgroup is non-freezable, so we can skip the
 187          * following check.
 188          */
 189         if (!freezer->css.cgroup->parent)
 190                 goto out;
 191
 192         spin_lock_irq(&freezer->lock);
 193         BUG_ON(freezer->state == CGROUP_FROZEN);
 194
 195         /* Locking avoids race with FREEZING -> THAWED transitions. */
 196         if (freezer->state == CGROUP_FREEZING)
 197                 freeze_task(task);
 198
 199         spin_unlock_irq(&freezer->lock);
 200 out:
 201         rcu_read_unlock();
 202 }
 203
 204 /*
 205  * caller must hold freezer->lock
 206  */
 207 static void update_if_frozen(struct cgroup *cgroup,
 208                                  struct freezer *freezer)
 209 {
 210         struct cgroup_iter it;
 211         struct task_struct *task;
 212         unsigned int nfrozen = 0, ntotal = 0;
 213         enum freezer_state old_state = freezer->state;
 214
 215         cgroup_iter_start(cgroup, &it);
 216         while ((task = cgroup_iter_next(cgroup, &it))) {
 217                 if (freezing(task)) {
 218                         ntotal++;
 219                         /*
 220                          * freezer_should_skip() indicates that the task
 221                          * should be skipped when determining freezing
 222                          * completion.  Consider it frozen in addition to
 223                          * the usual frozen condition.
 224                          */
 225                         if (frozen(task) || task_is_stopped_or_traced(task) ||
 226                             freezer_should_skip(task))
 227                                 nfrozen++;
 228                 }
 229         }
 230
 231         if (old_state == CGROUP_THAWED) {
 232                 BUG_ON(nfrozen > 0);
 233         } else if (old_state == CGROUP_FREEZING) {
 234                 if (nfrozen == ntotal)
 235                         freezer->state = CGROUP_FROZEN;
 236         } else { /* old_state == CGROUP_FROZEN */
 237                 BUG_ON(nfrozen != ntotal);
 238         }
 239
 240         cgroup_iter_end(cgroup, &it);
 241 }
 242
 243 static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
 244                         struct seq_file *m)
 245 {
 246         struct freezer *freezer;
 247         enum freezer_state state;
 248
 249         if (!cgroup_lock_live_group(cgroup))
 250                 return -ENODEV;
 251
 252         freezer = cgroup_freezer(cgroup);
 253         spin_lock_irq(&freezer->lock);
 254         state = freezer->state;
 255         if (state == CGROUP_FREEZING) {
 256                 /* We change from FREEZING to FROZEN lazily if the cgroup was
 257                  * only partially frozen when we exitted write. */
 258                 update_if_frozen(cgroup, freezer);
 259                 state = freezer->state;
 260         }
 261         spin_unlock_irq(&freezer->lock);
 262         cgroup_unlock();
 263
 264         seq_puts(m, freezer_state_strs[state]);
 265         seq_putc(m, '\n');
 266         return 0;
 267 }
 268
 269 static void freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
 270 {
 271         struct cgroup_iter it;
 272         struct task_struct *task;
 273
 274         cgroup_iter_start(cgroup, &it);
 275         while ((task = cgroup_iter_next(cgroup, &it)))
 276                 freeze_task(task);
 277         cgroup_iter_end(cgroup, &it);
 278 }
 279
 280 static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
 281 {
 282         struct cgroup_iter it;
 283         struct task_struct *task;
 284
 285         cgroup_iter_start(cgroup, &it);
 286         while ((task = cgroup_iter_next(cgroup, &it)))
 287                 __thaw_task(task);
 288         cgroup_iter_end(cgroup, &it);
 289 }
 290
 291 static void freezer_change_state(struct cgroup *cgroup,
 292                                  enum freezer_state goal_state)
 293 {
 294         struct freezer *freezer = cgroup_freezer(cgroup);
 295
 296         spin_lock_irq(&freezer->lock);
 297
 298         update_if_frozen(cgroup, freezer);
 299
 300         switch (goal_state) {
 301         case CGROUP_THAWED:
 302                 if (freezer->state != CGROUP_THAWED)
 303                         atomic_dec(&system_freezing_cnt);
 304                 freezer->state = CGROUP_THAWED;
 305                 unfreeze_cgroup(cgroup, freezer);
 306                 break;
 307         case CGROUP_FROZEN:
 308                 if (freezer->state == CGROUP_THAWED)
 309                         atomic_inc(&system_freezing_cnt);
 310                 freezer->state = CGROUP_FREEZING;
 311                 freeze_cgroup(cgroup, freezer);
 312                 break;
 313         default:
 314                 BUG();
 315         }
 316
 317         spin_unlock_irq(&freezer->lock);
 318 }
 319
 320 static int freezer_write(struct cgroup *cgroup,
 321                          struct cftype *cft,
 322                          const char *buffer)
 323 {
 324         enum freezer_state goal_state;
 325
 326         if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
 327                 goal_state = CGROUP_THAWED;
 328         else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
 329                 goal_state = CGROUP_FROZEN;
 330         else
 331                 return -EINVAL;
 332
 333         if (!cgroup_lock_live_group(cgroup))
 334                 return -ENODEV;
 335         freezer_change_state(cgroup, goal_state);
 336         cgroup_unlock();
 337         return 0;
 338 }
 339
 340 static struct cftype files[] = {
 341         {
 342                 .name = "state",
 343                 .flags = CFTYPE_NOT_ON_ROOT,
 344                 .read_seq_string = freezer_read,
 345                 .write_string = freezer_write,
 346         },
 347         { }     /* terminate */
 348 };
 349
 350 struct cgroup_subsys freezer_subsys = {
 351         .name           = "freezer",
 352         .create         = freezer_create,
 353         .destroy        = freezer_destroy,
 354         .subsys_id      = freezer_subsys_id,
 355         .can_attach     = freezer_can_attach,
 356         .fork           = freezer_fork,
 357         .base_cftypes   = files,
 358
 359         /*
 360          * freezer subsys doesn't handle hierarchy at all.  Frozen state
 361          * should be inherited through the hierarchy - if a parent is
 362          * frozen, all its children should be frozen.  Fix it and remove
 363          * the following.
 364          */
 365         .broken_hierarchy = true,
 366 };