| 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 | #include <linux/mutex.h> |
| 25 | |
| 26 | /* |
| 27 | * A cgroup is freezing if any FREEZING flags are set. FREEZING_SELF is |
| 28 | * set if "FROZEN" is written to freezer.state cgroupfs file, and cleared |
| 29 | * for "THAWED". FREEZING_PARENT is set if the parent freezer is FREEZING |
| 30 | * for whatever reason. IOW, a cgroup has FREEZING_PARENT set if one of |
| 31 | * its ancestors has FREEZING_SELF set. |
| 32 | */ |
| 33 | enum freezer_state_flags { |
| 34 | CGROUP_FREEZER_ONLINE = (1 << 0), /* freezer is fully online */ |
| 35 | CGROUP_FREEZING_SELF = (1 << 1), /* this freezer is freezing */ |
| 36 | CGROUP_FREEZING_PARENT = (1 << 2), /* the parent freezer is freezing */ |
| 37 | CGROUP_FROZEN = (1 << 3), /* this and its descendants frozen */ |
| 38 | |
| 39 | /* mask for all FREEZING flags */ |
| 40 | CGROUP_FREEZING = CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT, |
| 41 | }; |
| 42 | |
| 43 | struct freezer { |
| 44 | struct cgroup_subsys_state css; |
| 45 | unsigned int state; |
| 46 | }; |
| 47 | |
| 48 | static DEFINE_MUTEX(freezer_mutex); |
| 49 | |
| 50 | static inline struct freezer *css_freezer(struct cgroup_subsys_state *css) |
| 51 | { |
| 52 | return css ? container_of(css, struct freezer, css) : NULL; |
| 53 | } |
| 54 | |
| 55 | static inline struct freezer *task_freezer(struct task_struct *task) |
| 56 | { |
| 57 | return css_freezer(task_css(task, freezer_cgrp_id)); |
| 58 | } |
| 59 | |
| 60 | static struct freezer *parent_freezer(struct freezer *freezer) |
| 61 | { |
| 62 | return css_freezer(freezer->css.parent); |
| 63 | } |
| 64 | |
| 65 | bool cgroup_freezing(struct task_struct *task) |
| 66 | { |
| 67 | bool ret; |
| 68 | |
| 69 | rcu_read_lock(); |
| 70 | ret = task_freezer(task)->state & CGROUP_FREEZING; |
| 71 | rcu_read_unlock(); |
| 72 | |
| 73 | return ret; |
| 74 | } |
| 75 | |
| 76 | static const char *freezer_state_strs(unsigned int state) |
| 77 | { |
| 78 | if (state & CGROUP_FROZEN) |
| 79 | return "FROZEN"; |
| 80 | if (state & CGROUP_FREEZING) |
| 81 | return "FREEZING"; |
| 82 | return "THAWED"; |
| 83 | }; |
| 84 | |
| 85 | static struct cgroup_subsys_state * |
| 86 | freezer_css_alloc(struct cgroup_subsys_state *parent_css) |
| 87 | { |
| 88 | struct freezer *freezer; |
| 89 | |
| 90 | freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL); |
| 91 | if (!freezer) |
| 92 | return ERR_PTR(-ENOMEM); |
| 93 | |
| 94 | return &freezer->css; |
| 95 | } |
| 96 | |
| 97 | /** |
| 98 | * freezer_css_online - commit creation of a freezer css |
| 99 | * @css: css being created |
| 100 | * |
| 101 | * We're committing to creation of @css. Mark it online and inherit |
| 102 | * parent's freezing state while holding both parent's and our |
| 103 | * freezer->lock. |
| 104 | */ |
| 105 | static int freezer_css_online(struct cgroup_subsys_state *css) |
| 106 | { |
| 107 | struct freezer *freezer = css_freezer(css); |
| 108 | struct freezer *parent = parent_freezer(freezer); |
| 109 | |
| 110 | mutex_lock(&freezer_mutex); |
| 111 | |
| 112 | freezer->state |= CGROUP_FREEZER_ONLINE; |
| 113 | |
| 114 | if (parent && (parent->state & CGROUP_FREEZING)) { |
| 115 | freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN; |
| 116 | atomic_inc(&system_freezing_cnt); |
| 117 | } |
| 118 | |
| 119 | mutex_unlock(&freezer_mutex); |
| 120 | return 0; |
| 121 | } |
| 122 | |
| 123 | /** |
| 124 | * freezer_css_offline - initiate destruction of a freezer css |
| 125 | * @css: css being destroyed |
| 126 | * |
| 127 | * @css is going away. Mark it dead and decrement system_freezing_count if |
| 128 | * it was holding one. |
| 129 | */ |
| 130 | static void freezer_css_offline(struct cgroup_subsys_state *css) |
| 131 | { |
| 132 | struct freezer *freezer = css_freezer(css); |
| 133 | |
| 134 | mutex_lock(&freezer_mutex); |
| 135 | |
| 136 | if (freezer->state & CGROUP_FREEZING) |
| 137 | atomic_dec(&system_freezing_cnt); |
| 138 | |
| 139 | freezer->state = 0; |
| 140 | |
| 141 | mutex_unlock(&freezer_mutex); |
| 142 | } |
| 143 | |
| 144 | static void freezer_css_free(struct cgroup_subsys_state *css) |
| 145 | { |
| 146 | kfree(css_freezer(css)); |
| 147 | } |
| 148 | |
| 149 | /* |
| 150 | * Tasks can be migrated into a different freezer anytime regardless of its |
| 151 | * current state. freezer_attach() is responsible for making new tasks |
| 152 | * conform to the current state. |
| 153 | * |
| 154 | * Freezer state changes and task migration are synchronized via |
| 155 | * @freezer->lock. freezer_attach() makes the new tasks conform to the |
| 156 | * current state and all following state changes can see the new tasks. |
| 157 | */ |
| 158 | static void freezer_attach(struct cgroup_taskset *tset) |
| 159 | { |
| 160 | struct task_struct *task; |
| 161 | struct cgroup_subsys_state *new_css; |
| 162 | |
| 163 | mutex_lock(&freezer_mutex); |
| 164 | |
| 165 | /* |
| 166 | * Make the new tasks conform to the current state of @new_css. |
| 167 | * For simplicity, when migrating any task to a FROZEN cgroup, we |
| 168 | * revert it to FREEZING and let update_if_frozen() determine the |
| 169 | * correct state later. |
| 170 | * |
| 171 | * Tasks in @tset are on @new_css but may not conform to its |
| 172 | * current state before executing the following - !frozen tasks may |
| 173 | * be visible in a FROZEN cgroup and frozen tasks in a THAWED one. |
| 174 | */ |
| 175 | cgroup_taskset_for_each(task, new_css, tset) { |
| 176 | struct freezer *freezer = css_freezer(new_css); |
| 177 | |
| 178 | if (!(freezer->state & CGROUP_FREEZING)) { |
| 179 | __thaw_task(task); |
| 180 | } else { |
| 181 | freeze_task(task); |
| 182 | /* clear FROZEN and propagate upwards */ |
| 183 | while (freezer && (freezer->state & CGROUP_FROZEN)) { |
| 184 | freezer->state &= ~CGROUP_FROZEN; |
| 185 | freezer = parent_freezer(freezer); |
| 186 | } |
| 187 | } |
| 188 | } |
| 189 | |
| 190 | mutex_unlock(&freezer_mutex); |
| 191 | } |
| 192 | |
| 193 | /** |
| 194 | * freezer_fork - cgroup post fork callback |
| 195 | * @task: a task which has just been forked |
| 196 | * |
| 197 | * @task has just been created and should conform to the current state of |
| 198 | * the cgroup_freezer it belongs to. This function may race against |
| 199 | * freezer_attach(). Losing to freezer_attach() means that we don't have |
| 200 | * to do anything as freezer_attach() will put @task into the appropriate |
| 201 | * state. |
| 202 | */ |
| 203 | static void freezer_fork(struct task_struct *task) |
| 204 | { |
| 205 | struct freezer *freezer; |
| 206 | |
| 207 | /* |
| 208 | * The root cgroup is non-freezable, so we can skip locking the |
| 209 | * freezer. This is safe regardless of race with task migration. |
| 210 | * If we didn't race or won, skipping is obviously the right thing |
| 211 | * to do. If we lost and root is the new cgroup, noop is still the |
| 212 | * right thing to do. |
| 213 | */ |
| 214 | if (task_css_is_root(task, freezer_cgrp_id)) |
| 215 | return; |
| 216 | |
| 217 | mutex_lock(&freezer_mutex); |
| 218 | rcu_read_lock(); |
| 219 | |
| 220 | freezer = task_freezer(task); |
| 221 | if (freezer->state & CGROUP_FREEZING) |
| 222 | freeze_task(task); |
| 223 | |
| 224 | rcu_read_unlock(); |
| 225 | mutex_unlock(&freezer_mutex); |
| 226 | } |
| 227 | |
| 228 | /** |
| 229 | * update_if_frozen - update whether a cgroup finished freezing |
| 230 | * @css: css of interest |
| 231 | * |
| 232 | * Once FREEZING is initiated, transition to FROZEN is lazily updated by |
| 233 | * calling this function. If the current state is FREEZING but not FROZEN, |
| 234 | * this function checks whether all tasks of this cgroup and the descendant |
| 235 | * cgroups finished freezing and, if so, sets FROZEN. |
| 236 | * |
| 237 | * The caller is responsible for grabbing RCU read lock and calling |
| 238 | * update_if_frozen() on all descendants prior to invoking this function. |
| 239 | * |
| 240 | * Task states and freezer state might disagree while tasks are being |
| 241 | * migrated into or out of @css, so we can't verify task states against |
| 242 | * @freezer state here. See freezer_attach() for details. |
| 243 | */ |
| 244 | static void update_if_frozen(struct cgroup_subsys_state *css) |
| 245 | { |
| 246 | struct freezer *freezer = css_freezer(css); |
| 247 | struct cgroup_subsys_state *pos; |
| 248 | struct css_task_iter it; |
| 249 | struct task_struct *task; |
| 250 | |
| 251 | lockdep_assert_held(&freezer_mutex); |
| 252 | |
| 253 | if (!(freezer->state & CGROUP_FREEZING) || |
| 254 | (freezer->state & CGROUP_FROZEN)) |
| 255 | return; |
| 256 | |
| 257 | /* are all (live) children frozen? */ |
| 258 | rcu_read_lock(); |
| 259 | css_for_each_child(pos, css) { |
| 260 | struct freezer *child = css_freezer(pos); |
| 261 | |
| 262 | if ((child->state & CGROUP_FREEZER_ONLINE) && |
| 263 | !(child->state & CGROUP_FROZEN)) { |
| 264 | rcu_read_unlock(); |
| 265 | return; |
| 266 | } |
| 267 | } |
| 268 | rcu_read_unlock(); |
| 269 | |
| 270 | /* are all tasks frozen? */ |
| 271 | css_task_iter_start(css, &it); |
| 272 | |
| 273 | while ((task = css_task_iter_next(&it))) { |
| 274 | if (freezing(task)) { |
| 275 | /* |
| 276 | * freezer_should_skip() indicates that the task |
| 277 | * should be skipped when determining freezing |
| 278 | * completion. Consider it frozen in addition to |
| 279 | * the usual frozen condition. |
| 280 | */ |
| 281 | if (!frozen(task) && !freezer_should_skip(task)) |
| 282 | goto out_iter_end; |
| 283 | } |
| 284 | } |
| 285 | |
| 286 | freezer->state |= CGROUP_FROZEN; |
| 287 | out_iter_end: |
| 288 | css_task_iter_end(&it); |
| 289 | } |
| 290 | |
| 291 | static int freezer_read(struct seq_file *m, void *v) |
| 292 | { |
| 293 | struct cgroup_subsys_state *css = seq_css(m), *pos; |
| 294 | |
| 295 | mutex_lock(&freezer_mutex); |
| 296 | rcu_read_lock(); |
| 297 | |
| 298 | /* update states bottom-up */ |
| 299 | css_for_each_descendant_post(pos, css) { |
| 300 | if (!css_tryget_online(pos)) |
| 301 | continue; |
| 302 | rcu_read_unlock(); |
| 303 | |
| 304 | update_if_frozen(pos); |
| 305 | |
| 306 | rcu_read_lock(); |
| 307 | css_put(pos); |
| 308 | } |
| 309 | |
| 310 | rcu_read_unlock(); |
| 311 | mutex_unlock(&freezer_mutex); |
| 312 | |
| 313 | seq_puts(m, freezer_state_strs(css_freezer(css)->state)); |
| 314 | seq_putc(m, '\n'); |
| 315 | return 0; |
| 316 | } |
| 317 | |
| 318 | static void freeze_cgroup(struct freezer *freezer) |
| 319 | { |
| 320 | struct css_task_iter it; |
| 321 | struct task_struct *task; |
| 322 | |
| 323 | css_task_iter_start(&freezer->css, &it); |
| 324 | while ((task = css_task_iter_next(&it))) |
| 325 | freeze_task(task); |
| 326 | css_task_iter_end(&it); |
| 327 | } |
| 328 | |
| 329 | static void unfreeze_cgroup(struct freezer *freezer) |
| 330 | { |
| 331 | struct css_task_iter it; |
| 332 | struct task_struct *task; |
| 333 | |
| 334 | css_task_iter_start(&freezer->css, &it); |
| 335 | while ((task = css_task_iter_next(&it))) |
| 336 | __thaw_task(task); |
| 337 | css_task_iter_end(&it); |
| 338 | } |
| 339 | |
| 340 | /** |
| 341 | * freezer_apply_state - apply state change to a single cgroup_freezer |
| 342 | * @freezer: freezer to apply state change to |
| 343 | * @freeze: whether to freeze or unfreeze |
| 344 | * @state: CGROUP_FREEZING_* flag to set or clear |
| 345 | * |
| 346 | * Set or clear @state on @cgroup according to @freeze, and perform |
| 347 | * freezing or thawing as necessary. |
| 348 | */ |
| 349 | static void freezer_apply_state(struct freezer *freezer, bool freeze, |
| 350 | unsigned int state) |
| 351 | { |
| 352 | /* also synchronizes against task migration, see freezer_attach() */ |
| 353 | lockdep_assert_held(&freezer_mutex); |
| 354 | |
| 355 | if (!(freezer->state & CGROUP_FREEZER_ONLINE)) |
| 356 | return; |
| 357 | |
| 358 | if (freeze) { |
| 359 | if (!(freezer->state & CGROUP_FREEZING)) |
| 360 | atomic_inc(&system_freezing_cnt); |
| 361 | freezer->state |= state; |
| 362 | freeze_cgroup(freezer); |
| 363 | } else { |
| 364 | bool was_freezing = freezer->state & CGROUP_FREEZING; |
| 365 | |
| 366 | freezer->state &= ~state; |
| 367 | |
| 368 | if (!(freezer->state & CGROUP_FREEZING)) { |
| 369 | if (was_freezing) |
| 370 | atomic_dec(&system_freezing_cnt); |
| 371 | freezer->state &= ~CGROUP_FROZEN; |
| 372 | unfreeze_cgroup(freezer); |
| 373 | } |
| 374 | } |
| 375 | } |
| 376 | |
| 377 | /** |
| 378 | * freezer_change_state - change the freezing state of a cgroup_freezer |
| 379 | * @freezer: freezer of interest |
| 380 | * @freeze: whether to freeze or thaw |
| 381 | * |
| 382 | * Freeze or thaw @freezer according to @freeze. The operations are |
| 383 | * recursive - all descendants of @freezer will be affected. |
| 384 | */ |
| 385 | static void freezer_change_state(struct freezer *freezer, bool freeze) |
| 386 | { |
| 387 | struct cgroup_subsys_state *pos; |
| 388 | |
| 389 | /* |
| 390 | * Update all its descendants in pre-order traversal. Each |
| 391 | * descendant will try to inherit its parent's FREEZING state as |
| 392 | * CGROUP_FREEZING_PARENT. |
| 393 | */ |
| 394 | mutex_lock(&freezer_mutex); |
| 395 | rcu_read_lock(); |
| 396 | css_for_each_descendant_pre(pos, &freezer->css) { |
| 397 | struct freezer *pos_f = css_freezer(pos); |
| 398 | struct freezer *parent = parent_freezer(pos_f); |
| 399 | |
| 400 | if (!css_tryget_online(pos)) |
| 401 | continue; |
| 402 | rcu_read_unlock(); |
| 403 | |
| 404 | if (pos_f == freezer) |
| 405 | freezer_apply_state(pos_f, freeze, |
| 406 | CGROUP_FREEZING_SELF); |
| 407 | else |
| 408 | freezer_apply_state(pos_f, |
| 409 | parent->state & CGROUP_FREEZING, |
| 410 | CGROUP_FREEZING_PARENT); |
| 411 | |
| 412 | rcu_read_lock(); |
| 413 | css_put(pos); |
| 414 | } |
| 415 | rcu_read_unlock(); |
| 416 | mutex_unlock(&freezer_mutex); |
| 417 | } |
| 418 | |
| 419 | static ssize_t freezer_write(struct kernfs_open_file *of, |
| 420 | char *buf, size_t nbytes, loff_t off) |
| 421 | { |
| 422 | bool freeze; |
| 423 | |
| 424 | buf = strstrip(buf); |
| 425 | |
| 426 | if (strcmp(buf, freezer_state_strs(0)) == 0) |
| 427 | freeze = false; |
| 428 | else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0) |
| 429 | freeze = true; |
| 430 | else |
| 431 | return -EINVAL; |
| 432 | |
| 433 | freezer_change_state(css_freezer(of_css(of)), freeze); |
| 434 | return nbytes; |
| 435 | } |
| 436 | |
| 437 | static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css, |
| 438 | struct cftype *cft) |
| 439 | { |
| 440 | struct freezer *freezer = css_freezer(css); |
| 441 | |
| 442 | return (bool)(freezer->state & CGROUP_FREEZING_SELF); |
| 443 | } |
| 444 | |
| 445 | static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css, |
| 446 | struct cftype *cft) |
| 447 | { |
| 448 | struct freezer *freezer = css_freezer(css); |
| 449 | |
| 450 | return (bool)(freezer->state & CGROUP_FREEZING_PARENT); |
| 451 | } |
| 452 | |
| 453 | static struct cftype files[] = { |
| 454 | { |
| 455 | .name = "state", |
| 456 | .flags = CFTYPE_NOT_ON_ROOT, |
| 457 | .seq_show = freezer_read, |
| 458 | .write = freezer_write, |
| 459 | }, |
| 460 | { |
| 461 | .name = "self_freezing", |
| 462 | .flags = CFTYPE_NOT_ON_ROOT, |
| 463 | .read_u64 = freezer_self_freezing_read, |
| 464 | }, |
| 465 | { |
| 466 | .name = "parent_freezing", |
| 467 | .flags = CFTYPE_NOT_ON_ROOT, |
| 468 | .read_u64 = freezer_parent_freezing_read, |
| 469 | }, |
| 470 | { } /* terminate */ |
| 471 | }; |
| 472 | |
| 473 | struct cgroup_subsys freezer_cgrp_subsys = { |
| 474 | .css_alloc = freezer_css_alloc, |
| 475 | .css_online = freezer_css_online, |
| 476 | .css_offline = freezer_css_offline, |
| 477 | .css_free = freezer_css_free, |
| 478 | .attach = freezer_attach, |
| 479 | .fork = freezer_fork, |
| 480 | .legacy_cftypes = files, |
| 481 | }; |