| 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 | /* task is frozen or will freeze immediately when next it gets woken */ |
| 154 | static bool is_task_frozen_enough(struct task_struct *task) |
| 155 | { |
| 156 | return frozen(task) || |
| 157 | (task_is_stopped_or_traced(task) && freezing(task)); |
| 158 | } |
| 159 | |
| 160 | /* |
| 161 | * The call to cgroup_lock() in the freezer.state write method prevents |
| 162 | * a write to that file racing against an attach, and hence the |
| 163 | * can_attach() result will remain valid until the attach completes. |
| 164 | */ |
| 165 | static int freezer_can_attach(struct cgroup *new_cgroup, |
| 166 | struct cgroup_taskset *tset) |
| 167 | { |
| 168 | struct freezer *freezer; |
| 169 | struct task_struct *task; |
| 170 | |
| 171 | /* |
| 172 | * Anything frozen can't move or be moved to/from. |
| 173 | */ |
| 174 | cgroup_taskset_for_each(task, new_cgroup, tset) |
| 175 | if (cgroup_freezing(task)) |
| 176 | return -EBUSY; |
| 177 | |
| 178 | freezer = cgroup_freezer(new_cgroup); |
| 179 | if (freezer->state != CGROUP_THAWED) |
| 180 | return -EBUSY; |
| 181 | |
| 182 | return 0; |
| 183 | } |
| 184 | |
| 185 | static void freezer_fork(struct task_struct *task) |
| 186 | { |
| 187 | struct freezer *freezer; |
| 188 | |
| 189 | /* |
| 190 | * No lock is needed, since the task isn't on tasklist yet, |
| 191 | * so it can't be moved to another cgroup, which means the |
| 192 | * freezer won't be removed and will be valid during this |
| 193 | * function call. Nevertheless, apply RCU read-side critical |
| 194 | * section to suppress RCU lockdep false positives. |
| 195 | */ |
| 196 | rcu_read_lock(); |
| 197 | freezer = task_freezer(task); |
| 198 | rcu_read_unlock(); |
| 199 | |
| 200 | /* |
| 201 | * The root cgroup is non-freezable, so we can skip the |
| 202 | * following check. |
| 203 | */ |
| 204 | if (!freezer->css.cgroup->parent) |
| 205 | return; |
| 206 | |
| 207 | spin_lock_irq(&freezer->lock); |
| 208 | BUG_ON(freezer->state == CGROUP_FROZEN); |
| 209 | |
| 210 | /* Locking avoids race with FREEZING -> THAWED transitions. */ |
| 211 | if (freezer->state == CGROUP_FREEZING) |
| 212 | freeze_task(task); |
| 213 | spin_unlock_irq(&freezer->lock); |
| 214 | } |
| 215 | |
| 216 | /* |
| 217 | * caller must hold freezer->lock |
| 218 | */ |
| 219 | static void update_if_frozen(struct cgroup *cgroup, |
| 220 | struct freezer *freezer) |
| 221 | { |
| 222 | struct cgroup_iter it; |
| 223 | struct task_struct *task; |
| 224 | unsigned int nfrozen = 0, ntotal = 0; |
| 225 | enum freezer_state old_state = freezer->state; |
| 226 | |
| 227 | cgroup_iter_start(cgroup, &it); |
| 228 | while ((task = cgroup_iter_next(cgroup, &it))) { |
| 229 | ntotal++; |
| 230 | if (freezing(task) && is_task_frozen_enough(task)) |
| 231 | nfrozen++; |
| 232 | } |
| 233 | |
| 234 | if (old_state == CGROUP_THAWED) { |
| 235 | BUG_ON(nfrozen > 0); |
| 236 | } else if (old_state == CGROUP_FREEZING) { |
| 237 | if (nfrozen == ntotal) |
| 238 | freezer->state = CGROUP_FROZEN; |
| 239 | } else { /* old_state == CGROUP_FROZEN */ |
| 240 | BUG_ON(nfrozen != ntotal); |
| 241 | } |
| 242 | |
| 243 | cgroup_iter_end(cgroup, &it); |
| 244 | } |
| 245 | |
| 246 | static int freezer_read(struct cgroup *cgroup, struct cftype *cft, |
| 247 | struct seq_file *m) |
| 248 | { |
| 249 | struct freezer *freezer; |
| 250 | enum freezer_state state; |
| 251 | |
| 252 | if (!cgroup_lock_live_group(cgroup)) |
| 253 | return -ENODEV; |
| 254 | |
| 255 | freezer = cgroup_freezer(cgroup); |
| 256 | spin_lock_irq(&freezer->lock); |
| 257 | state = freezer->state; |
| 258 | if (state == CGROUP_FREEZING) { |
| 259 | /* We change from FREEZING to FROZEN lazily if the cgroup was |
| 260 | * only partially frozen when we exitted write. */ |
| 261 | update_if_frozen(cgroup, freezer); |
| 262 | state = freezer->state; |
| 263 | } |
| 264 | spin_unlock_irq(&freezer->lock); |
| 265 | cgroup_unlock(); |
| 266 | |
| 267 | seq_puts(m, freezer_state_strs[state]); |
| 268 | seq_putc(m, '\n'); |
| 269 | return 0; |
| 270 | } |
| 271 | |
| 272 | static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
| 273 | { |
| 274 | struct cgroup_iter it; |
| 275 | struct task_struct *task; |
| 276 | unsigned int num_cant_freeze_now = 0; |
| 277 | |
| 278 | cgroup_iter_start(cgroup, &it); |
| 279 | while ((task = cgroup_iter_next(cgroup, &it))) { |
| 280 | if (!freeze_task(task)) |
| 281 | continue; |
| 282 | if (is_task_frozen_enough(task)) |
| 283 | continue; |
| 284 | if (!freezing(task) && !freezer_should_skip(task)) |
| 285 | num_cant_freeze_now++; |
| 286 | } |
| 287 | cgroup_iter_end(cgroup, &it); |
| 288 | |
| 289 | return num_cant_freeze_now ? -EBUSY : 0; |
| 290 | } |
| 291 | |
| 292 | static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) |
| 293 | { |
| 294 | struct cgroup_iter it; |
| 295 | struct task_struct *task; |
| 296 | |
| 297 | cgroup_iter_start(cgroup, &it); |
| 298 | while ((task = cgroup_iter_next(cgroup, &it))) |
| 299 | __thaw_task(task); |
| 300 | cgroup_iter_end(cgroup, &it); |
| 301 | } |
| 302 | |
| 303 | static int freezer_change_state(struct cgroup *cgroup, |
| 304 | enum freezer_state goal_state) |
| 305 | { |
| 306 | struct freezer *freezer; |
| 307 | int retval = 0; |
| 308 | |
| 309 | freezer = cgroup_freezer(cgroup); |
| 310 | |
| 311 | spin_lock_irq(&freezer->lock); |
| 312 | |
| 313 | update_if_frozen(cgroup, freezer); |
| 314 | |
| 315 | switch (goal_state) { |
| 316 | case CGROUP_THAWED: |
| 317 | if (freezer->state != CGROUP_THAWED) |
| 318 | atomic_dec(&system_freezing_cnt); |
| 319 | freezer->state = CGROUP_THAWED; |
| 320 | unfreeze_cgroup(cgroup, freezer); |
| 321 | break; |
| 322 | case CGROUP_FROZEN: |
| 323 | if (freezer->state == CGROUP_THAWED) |
| 324 | atomic_inc(&system_freezing_cnt); |
| 325 | freezer->state = CGROUP_FREEZING; |
| 326 | retval = try_to_freeze_cgroup(cgroup, freezer); |
| 327 | break; |
| 328 | default: |
| 329 | BUG(); |
| 330 | } |
| 331 | |
| 332 | spin_unlock_irq(&freezer->lock); |
| 333 | |
| 334 | return retval; |
| 335 | } |
| 336 | |
| 337 | static int freezer_write(struct cgroup *cgroup, |
| 338 | struct cftype *cft, |
| 339 | const char *buffer) |
| 340 | { |
| 341 | int retval; |
| 342 | enum freezer_state goal_state; |
| 343 | |
| 344 | if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0) |
| 345 | goal_state = CGROUP_THAWED; |
| 346 | else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0) |
| 347 | goal_state = CGROUP_FROZEN; |
| 348 | else |
| 349 | return -EINVAL; |
| 350 | |
| 351 | if (!cgroup_lock_live_group(cgroup)) |
| 352 | return -ENODEV; |
| 353 | retval = freezer_change_state(cgroup, goal_state); |
| 354 | cgroup_unlock(); |
| 355 | return retval; |
| 356 | } |
| 357 | |
| 358 | static struct cftype files[] = { |
| 359 | { |
| 360 | .name = "state", |
| 361 | .flags = CFTYPE_NOT_ON_ROOT, |
| 362 | .read_seq_string = freezer_read, |
| 363 | .write_string = freezer_write, |
| 364 | }, |
| 365 | { } /* terminate */ |
| 366 | }; |
| 367 | |
| 368 | struct cgroup_subsys freezer_subsys = { |
| 369 | .name = "freezer", |
| 370 | .create = freezer_create, |
| 371 | .destroy = freezer_destroy, |
| 372 | .subsys_id = freezer_subsys_id, |
| 373 | .can_attach = freezer_can_attach, |
| 374 | .fork = freezer_fork, |
| 375 | .base_cftypes = files, |
| 376 | |
| 377 | /* |
| 378 | * freezer subsys doesn't handle hierarchy at all. Frozen state |
| 379 | * should be inherited through the hierarchy - if a parent is |
| 380 | * frozen, all its children should be frozen. Fix it and remove |
| 381 | * the following. |
| 382 | */ |
| 383 | .broken_hierarchy = true, |
| 384 | }; |