linux/block/blk-cgroup.c
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   1/*
   2 * Common Block IO controller cgroup interface
   3 *
   4 * Based on ideas and code from CFQ, CFS and BFQ:
   5 * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
   6 *
   7 * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
   8 *                    Paolo Valente <paolo.valente@unimore.it>
   9 *
  10 * Copyright (C) 2009 Vivek Goyal <vgoyal@redhat.com>
  11 *                    Nauman Rafique <nauman@google.com>
  12 */
  13#include <linux/ioprio.h>
  14#include <linux/kdev_t.h>
  15#include <linux/module.h>
  16#include <linux/err.h>
  17#include <linux/blkdev.h>
  18#include <linux/slab.h>
  19#include <linux/genhd.h>
  20#include <linux/delay.h>
  21#include <linux/atomic.h>
  22#include "blk-cgroup.h"
  23#include "blk.h"
  24
  25#define MAX_KEY_LEN 100
  26
  27static DEFINE_MUTEX(blkcg_pol_mutex);
  28
  29struct blkcg blkcg_root = { .cfq_weight = 2 * CFQ_WEIGHT_DEFAULT };
  30EXPORT_SYMBOL_GPL(blkcg_root);
  31
  32static struct blkcg_policy *blkcg_policy[BLKCG_MAX_POLS];
  33
  34struct blkcg *cgroup_to_blkcg(struct cgroup *cgroup)
  35{
  36        return container_of(cgroup_subsys_state(cgroup, blkio_subsys_id),
  37                            struct blkcg, css);
  38}
  39EXPORT_SYMBOL_GPL(cgroup_to_blkcg);
  40
  41static struct blkcg *task_blkcg(struct task_struct *tsk)
  42{
  43        return container_of(task_subsys_state(tsk, blkio_subsys_id),
  44                            struct blkcg, css);
  45}
  46
  47struct blkcg *bio_blkcg(struct bio *bio)
  48{
  49        if (bio && bio->bi_css)
  50                return container_of(bio->bi_css, struct blkcg, css);
  51        return task_blkcg(current);
  52}
  53EXPORT_SYMBOL_GPL(bio_blkcg);
  54
  55static bool blkcg_policy_enabled(struct request_queue *q,
  56                                 const struct blkcg_policy *pol)
  57{
  58        return pol && test_bit(pol->plid, q->blkcg_pols);
  59}
  60
  61/**
  62 * blkg_free - free a blkg
  63 * @blkg: blkg to free
  64 *
  65 * Free @blkg which may be partially allocated.
  66 */
  67static void blkg_free(struct blkcg_gq *blkg)
  68{
  69        int i;
  70
  71        if (!blkg)
  72                return;
  73
  74        for (i = 0; i < BLKCG_MAX_POLS; i++) {
  75                struct blkcg_policy *pol = blkcg_policy[i];
  76                struct blkg_policy_data *pd = blkg->pd[i];
  77
  78                if (!pd)
  79                        continue;
  80
  81                if (pol && pol->pd_exit_fn)
  82                        pol->pd_exit_fn(blkg);
  83
  84                kfree(pd);
  85        }
  86
  87        kfree(blkg);
  88}
  89
  90/**
  91 * blkg_alloc - allocate a blkg
  92 * @blkcg: block cgroup the new blkg is associated with
  93 * @q: request_queue the new blkg is associated with
  94 *
  95 * Allocate a new blkg assocating @blkcg and @q.
  96 */
  97static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q)
  98{
  99        struct blkcg_gq *blkg;
 100        int i;
 101
 102        /* alloc and init base part */
 103        blkg = kzalloc_node(sizeof(*blkg), GFP_ATOMIC, q->node);
 104        if (!blkg)
 105                return NULL;
 106
 107        blkg->q = q;
 108        INIT_LIST_HEAD(&blkg->q_node);
 109        blkg->blkcg = blkcg;
 110        blkg->refcnt = 1;
 111
 112        for (i = 0; i < BLKCG_MAX_POLS; i++) {
 113                struct blkcg_policy *pol = blkcg_policy[i];
 114                struct blkg_policy_data *pd;
 115
 116                if (!blkcg_policy_enabled(q, pol))
 117                        continue;
 118
 119                /* alloc per-policy data and attach it to blkg */
 120                pd = kzalloc_node(pol->pd_size, GFP_ATOMIC, q->node);
 121                if (!pd) {
 122                        blkg_free(blkg);
 123                        return NULL;
 124                }
 125
 126                blkg->pd[i] = pd;
 127                pd->blkg = blkg;
 128
 129                /* invoke per-policy init */
 130                if (blkcg_policy_enabled(blkg->q, pol))
 131                        pol->pd_init_fn(blkg);
 132        }
 133
 134        return blkg;
 135}
 136
 137static struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg,
 138                                      struct request_queue *q)
 139{
 140        struct blkcg_gq *blkg;
 141
 142        blkg = rcu_dereference(blkcg->blkg_hint);
 143        if (blkg && blkg->q == q)
 144                return blkg;
 145
 146        /*
 147         * Hint didn't match.  Look up from the radix tree.  Note that we
 148         * may not be holding queue_lock and thus are not sure whether
 149         * @blkg from blkg_tree has already been removed or not, so we
 150         * can't update hint to the lookup result.  Leave it to the caller.
 151         */
 152        blkg = radix_tree_lookup(&blkcg->blkg_tree, q->id);
 153        if (blkg && blkg->q == q)
 154                return blkg;
 155
 156        return NULL;
 157}
 158
 159/**
 160 * blkg_lookup - lookup blkg for the specified blkcg - q pair
 161 * @blkcg: blkcg of interest
 162 * @q: request_queue of interest
 163 *
 164 * Lookup blkg for the @blkcg - @q pair.  This function should be called
 165 * under RCU read lock and is guaranteed to return %NULL if @q is bypassing
 166 * - see blk_queue_bypass_start() for details.
 167 */
 168struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, struct request_queue *q)
 169{
 170        WARN_ON_ONCE(!rcu_read_lock_held());
 171
 172        if (unlikely(blk_queue_bypass(q)))
 173                return NULL;
 174        return __blkg_lookup(blkcg, q);
 175}
 176EXPORT_SYMBOL_GPL(blkg_lookup);
 177
 178static struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
 179                                             struct request_queue *q)
 180        __releases(q->queue_lock) __acquires(q->queue_lock)
 181{
 182        struct blkcg_gq *blkg;
 183        int ret;
 184
 185        WARN_ON_ONCE(!rcu_read_lock_held());
 186        lockdep_assert_held(q->queue_lock);
 187
 188        /* lookup and update hint on success, see __blkg_lookup() for details */
 189        blkg = __blkg_lookup(blkcg, q);
 190        if (blkg) {
 191                rcu_assign_pointer(blkcg->blkg_hint, blkg);
 192                return blkg;
 193        }
 194
 195        /* blkg holds a reference to blkcg */
 196        if (!css_tryget(&blkcg->css))
 197                return ERR_PTR(-EINVAL);
 198
 199        /* allocate */
 200        ret = -ENOMEM;
 201        blkg = blkg_alloc(blkcg, q);
 202        if (unlikely(!blkg))
 203                goto err_put;
 204
 205        /* insert */
 206        ret = radix_tree_preload(GFP_ATOMIC);
 207        if (ret)
 208                goto err_free;
 209
 210        spin_lock(&blkcg->lock);
 211        ret = radix_tree_insert(&blkcg->blkg_tree, q->id, blkg);
 212        if (likely(!ret)) {
 213                hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
 214                list_add(&blkg->q_node, &q->blkg_list);
 215        }
 216        spin_unlock(&blkcg->lock);
 217
 218        radix_tree_preload_end();
 219
 220        if (!ret)
 221                return blkg;
 222err_free:
 223        blkg_free(blkg);
 224err_put:
 225        css_put(&blkcg->css);
 226        return ERR_PTR(ret);
 227}
 228
 229struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
 230                                    struct request_queue *q)
 231{
 232        /*
 233         * This could be the first entry point of blkcg implementation and
 234         * we shouldn't allow anything to go through for a bypassing queue.
 235         */
 236        if (unlikely(blk_queue_bypass(q)))
 237                return ERR_PTR(blk_queue_dead(q) ? -EINVAL : -EBUSY);
 238        return __blkg_lookup_create(blkcg, q);
 239}
 240EXPORT_SYMBOL_GPL(blkg_lookup_create);
 241
 242static void blkg_destroy(struct blkcg_gq *blkg)
 243{
 244        struct blkcg *blkcg = blkg->blkcg;
 245
 246        lockdep_assert_held(blkg->q->queue_lock);
 247        lockdep_assert_held(&blkcg->lock);
 248
 249        /* Something wrong if we are trying to remove same group twice */
 250        WARN_ON_ONCE(list_empty(&blkg->q_node));
 251        WARN_ON_ONCE(hlist_unhashed(&blkg->blkcg_node));
 252
 253        radix_tree_delete(&blkcg->blkg_tree, blkg->q->id);
 254        list_del_init(&blkg->q_node);
 255        hlist_del_init_rcu(&blkg->blkcg_node);
 256
 257        /*
 258         * Both setting lookup hint to and clearing it from @blkg are done
 259         * under queue_lock.  If it's not pointing to @blkg now, it never
 260         * will.  Hint assignment itself can race safely.
 261         */
 262        if (rcu_dereference_raw(blkcg->blkg_hint) == blkg)
 263                rcu_assign_pointer(blkcg->blkg_hint, NULL);
 264
 265        /*
 266         * Put the reference taken at the time of creation so that when all
 267         * queues are gone, group can be destroyed.
 268         */
 269        blkg_put(blkg);
 270}
 271
 272/**
 273 * blkg_destroy_all - destroy all blkgs associated with a request_queue
 274 * @q: request_queue of interest
 275 *
 276 * Destroy all blkgs associated with @q.
 277 */
 278static void blkg_destroy_all(struct request_queue *q)
 279{
 280        struct blkcg_gq *blkg, *n;
 281
 282        lockdep_assert_held(q->queue_lock);
 283
 284        list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
 285                struct blkcg *blkcg = blkg->blkcg;
 286
 287                spin_lock(&blkcg->lock);
 288                blkg_destroy(blkg);
 289                spin_unlock(&blkcg->lock);
 290        }
 291}
 292
 293static void blkg_rcu_free(struct rcu_head *rcu_head)
 294{
 295        blkg_free(container_of(rcu_head, struct blkcg_gq, rcu_head));
 296}
 297
 298void __blkg_release(struct blkcg_gq *blkg)
 299{
 300        /* release the extra blkcg reference this blkg has been holding */
 301        css_put(&blkg->blkcg->css);
 302
 303        /*
 304         * A group is freed in rcu manner. But having an rcu lock does not
 305         * mean that one can access all the fields of blkg and assume these
 306         * are valid. For example, don't try to follow throtl_data and
 307         * request queue links.
 308         *
 309         * Having a reference to blkg under an rcu allows acess to only
 310         * values local to groups like group stats and group rate limits
 311         */
 312        call_rcu(&blkg->rcu_head, blkg_rcu_free);
 313}
 314EXPORT_SYMBOL_GPL(__blkg_release);
 315
 316static int blkcg_reset_stats(struct cgroup *cgroup, struct cftype *cftype,
 317                             u64 val)
 318{
 319        struct blkcg *blkcg = cgroup_to_blkcg(cgroup);
 320        struct blkcg_gq *blkg;
 321        struct hlist_node *n;
 322        int i;
 323
 324        mutex_lock(&blkcg_pol_mutex);
 325        spin_lock_irq(&blkcg->lock);
 326
 327        /*
 328         * Note that stat reset is racy - it doesn't synchronize against
 329         * stat updates.  This is a debug feature which shouldn't exist
 330         * anyway.  If you get hit by a race, retry.
 331         */
 332        hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
 333                for (i = 0; i < BLKCG_MAX_POLS; i++) {
 334                        struct blkcg_policy *pol = blkcg_policy[i];
 335
 336                        if (blkcg_policy_enabled(blkg->q, pol) &&
 337                            pol->pd_reset_stats_fn)
 338                                pol->pd_reset_stats_fn(blkg);
 339                }
 340        }
 341
 342        spin_unlock_irq(&blkcg->lock);
 343        mutex_unlock(&blkcg_pol_mutex);
 344        return 0;
 345}
 346
 347static const char *blkg_dev_name(struct blkcg_gq *blkg)
 348{
 349        /* some drivers (floppy) instantiate a queue w/o disk registered */
 350        if (blkg->q->backing_dev_info.dev)
 351                return dev_name(blkg->q->backing_dev_info.dev);
 352        return NULL;
 353}
 354
 355/**
 356 * blkcg_print_blkgs - helper for printing per-blkg data
 357 * @sf: seq_file to print to
 358 * @blkcg: blkcg of interest
 359 * @prfill: fill function to print out a blkg
 360 * @pol: policy in question
 361 * @data: data to be passed to @prfill
 362 * @show_total: to print out sum of prfill return values or not
 363 *
 364 * This function invokes @prfill on each blkg of @blkcg if pd for the
 365 * policy specified by @pol exists.  @prfill is invoked with @sf, the
 366 * policy data and @data.  If @show_total is %true, the sum of the return
 367 * values from @prfill is printed with "Total" label at the end.
 368 *
 369 * This is to be used to construct print functions for
 370 * cftype->read_seq_string method.
 371 */
 372void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
 373                       u64 (*prfill)(struct seq_file *,
 374                                     struct blkg_policy_data *, int),
 375                       const struct blkcg_policy *pol, int data,
 376                       bool show_total)
 377{
 378        struct blkcg_gq *blkg;
 379        struct hlist_node *n;
 380        u64 total = 0;
 381
 382        spin_lock_irq(&blkcg->lock);
 383        hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node)
 384                if (blkcg_policy_enabled(blkg->q, pol))
 385                        total += prfill(sf, blkg->pd[pol->plid], data);
 386        spin_unlock_irq(&blkcg->lock);
 387
 388        if (show_total)
 389                seq_printf(sf, "Total %llu\n", (unsigned long long)total);
 390}
 391EXPORT_SYMBOL_GPL(blkcg_print_blkgs);
 392
 393/**
 394 * __blkg_prfill_u64 - prfill helper for a single u64 value
 395 * @sf: seq_file to print to
 396 * @pd: policy private data of interest
 397 * @v: value to print
 398 *
 399 * Print @v to @sf for the device assocaited with @pd.
 400 */
 401u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v)
 402{
 403        const char *dname = blkg_dev_name(pd->blkg);
 404
 405        if (!dname)
 406                return 0;
 407
 408        seq_printf(sf, "%s %llu\n", dname, (unsigned long long)v);
 409        return v;
 410}
 411EXPORT_SYMBOL_GPL(__blkg_prfill_u64);
 412
 413/**
 414 * __blkg_prfill_rwstat - prfill helper for a blkg_rwstat
 415 * @sf: seq_file to print to
 416 * @pd: policy private data of interest
 417 * @rwstat: rwstat to print
 418 *
 419 * Print @rwstat to @sf for the device assocaited with @pd.
 420 */
 421u64 __blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
 422                         const struct blkg_rwstat *rwstat)
 423{
 424        static const char *rwstr[] = {
 425                [BLKG_RWSTAT_READ]      = "Read",
 426                [BLKG_RWSTAT_WRITE]     = "Write",
 427                [BLKG_RWSTAT_SYNC]      = "Sync",
 428                [BLKG_RWSTAT_ASYNC]     = "Async",
 429        };
 430        const char *dname = blkg_dev_name(pd->blkg);
 431        u64 v;
 432        int i;
 433
 434        if (!dname)
 435                return 0;
 436
 437        for (i = 0; i < BLKG_RWSTAT_NR; i++)
 438                seq_printf(sf, "%s %s %llu\n", dname, rwstr[i],
 439                           (unsigned long long)rwstat->cnt[i]);
 440
 441        v = rwstat->cnt[BLKG_RWSTAT_READ] + rwstat->cnt[BLKG_RWSTAT_WRITE];
 442        seq_printf(sf, "%s Total %llu\n", dname, (unsigned long long)v);
 443        return v;
 444}
 445
 446/**
 447 * blkg_prfill_stat - prfill callback for blkg_stat
 448 * @sf: seq_file to print to
 449 * @pd: policy private data of interest
 450 * @off: offset to the blkg_stat in @pd
 451 *
 452 * prfill callback for printing a blkg_stat.
 453 */
 454u64 blkg_prfill_stat(struct seq_file *sf, struct blkg_policy_data *pd, int off)
 455{
 456        return __blkg_prfill_u64(sf, pd, blkg_stat_read((void *)pd + off));
 457}
 458EXPORT_SYMBOL_GPL(blkg_prfill_stat);
 459
 460/**
 461 * blkg_prfill_rwstat - prfill callback for blkg_rwstat
 462 * @sf: seq_file to print to
 463 * @pd: policy private data of interest
 464 * @off: offset to the blkg_rwstat in @pd
 465 *
 466 * prfill callback for printing a blkg_rwstat.
 467 */
 468u64 blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
 469                       int off)
 470{
 471        struct blkg_rwstat rwstat = blkg_rwstat_read((void *)pd + off);
 472
 473        return __blkg_prfill_rwstat(sf, pd, &rwstat);
 474}
 475EXPORT_SYMBOL_GPL(blkg_prfill_rwstat);
 476
 477/**
 478 * blkg_conf_prep - parse and prepare for per-blkg config update
 479 * @blkcg: target block cgroup
 480 * @pol: target policy
 481 * @input: input string
 482 * @ctx: blkg_conf_ctx to be filled
 483 *
 484 * Parse per-blkg config update from @input and initialize @ctx with the
 485 * result.  @ctx->blkg points to the blkg to be updated and @ctx->v the new
 486 * value.  This function returns with RCU read lock and queue lock held and
 487 * must be paired with blkg_conf_finish().
 488 */
 489int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 490                   const char *input, struct blkg_conf_ctx *ctx)
 491        __acquires(rcu) __acquires(disk->queue->queue_lock)
 492{
 493        struct gendisk *disk;
 494        struct blkcg_gq *blkg;
 495        unsigned int major, minor;
 496        unsigned long long v;
 497        int part, ret;
 498
 499        if (sscanf(input, "%u:%u %llu", &major, &minor, &v) != 3)
 500                return -EINVAL;
 501
 502        disk = get_gendisk(MKDEV(major, minor), &part);
 503        if (!disk || part)
 504                return -EINVAL;
 505
 506        rcu_read_lock();
 507        spin_lock_irq(disk->queue->queue_lock);
 508
 509        if (blkcg_policy_enabled(disk->queue, pol))
 510                blkg = blkg_lookup_create(blkcg, disk->queue);
 511        else
 512                blkg = ERR_PTR(-EINVAL);
 513
 514        if (IS_ERR(blkg)) {
 515                ret = PTR_ERR(blkg);
 516                rcu_read_unlock();
 517                spin_unlock_irq(disk->queue->queue_lock);
 518                put_disk(disk);
 519                /*
 520                 * If queue was bypassing, we should retry.  Do so after a
 521                 * short msleep().  It isn't strictly necessary but queue
 522                 * can be bypassing for some time and it's always nice to
 523                 * avoid busy looping.
 524                 */
 525                if (ret == -EBUSY) {
 526                        msleep(10);
 527                        ret = restart_syscall();
 528                }
 529                return ret;
 530        }
 531
 532        ctx->disk = disk;
 533        ctx->blkg = blkg;
 534        ctx->v = v;
 535        return 0;
 536}
 537EXPORT_SYMBOL_GPL(blkg_conf_prep);
 538
 539/**
 540 * blkg_conf_finish - finish up per-blkg config update
 541 * @ctx: blkg_conf_ctx intiailized by blkg_conf_prep()
 542 *
 543 * Finish up after per-blkg config update.  This function must be paired
 544 * with blkg_conf_prep().
 545 */
 546void blkg_conf_finish(struct blkg_conf_ctx *ctx)
 547        __releases(ctx->disk->queue->queue_lock) __releases(rcu)
 548{
 549        spin_unlock_irq(ctx->disk->queue->queue_lock);
 550        rcu_read_unlock();
 551        put_disk(ctx->disk);
 552}
 553EXPORT_SYMBOL_GPL(blkg_conf_finish);
 554
 555struct cftype blkcg_files[] = {
 556        {
 557                .name = "reset_stats",
 558                .write_u64 = blkcg_reset_stats,
 559        },
 560        { }     /* terminate */
 561};
 562
 563/**
 564 * blkcg_pre_destroy - cgroup pre_destroy callback
 565 * @cgroup: cgroup of interest
 566 *
 567 * This function is called when @cgroup is about to go away and responsible
 568 * for shooting down all blkgs associated with @cgroup.  blkgs should be
 569 * removed while holding both q and blkcg locks.  As blkcg lock is nested
 570 * inside q lock, this function performs reverse double lock dancing.
 571 *
 572 * This is the blkcg counterpart of ioc_release_fn().
 573 */
 574static int blkcg_pre_destroy(struct cgroup *cgroup)
 575{
 576        struct blkcg *blkcg = cgroup_to_blkcg(cgroup);
 577
 578        spin_lock_irq(&blkcg->lock);
 579
 580        while (!hlist_empty(&blkcg->blkg_list)) {
 581                struct blkcg_gq *blkg = hlist_entry(blkcg->blkg_list.first,
 582                                                struct blkcg_gq, blkcg_node);
 583                struct request_queue *q = blkg->q;
 584
 585                if (spin_trylock(q->queue_lock)) {
 586                        blkg_destroy(blkg);
 587                        spin_unlock(q->queue_lock);
 588                } else {
 589                        spin_unlock_irq(&blkcg->lock);
 590                        cpu_relax();
 591                        spin_lock_irq(&blkcg->lock);
 592                }
 593        }
 594
 595        spin_unlock_irq(&blkcg->lock);
 596        return 0;
 597}
 598
 599static void blkcg_destroy(struct cgroup *cgroup)
 600{
 601        struct blkcg *blkcg = cgroup_to_blkcg(cgroup);
 602
 603        if (blkcg != &blkcg_root)
 604                kfree(blkcg);
 605}
 606
 607static struct cgroup_subsys_state *blkcg_create(struct cgroup *cgroup)
 608{
 609        static atomic64_t id_seq = ATOMIC64_INIT(0);
 610        struct blkcg *blkcg;
 611        struct cgroup *parent = cgroup->parent;
 612
 613        if (!parent) {
 614                blkcg = &blkcg_root;
 615                goto done;
 616        }
 617
 618        blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL);
 619        if (!blkcg)
 620                return ERR_PTR(-ENOMEM);
 621
 622        blkcg->cfq_weight = CFQ_WEIGHT_DEFAULT;
 623        blkcg->id = atomic64_inc_return(&id_seq); /* root is 0, start from 1 */
 624done:
 625        spin_lock_init(&blkcg->lock);
 626        INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_ATOMIC);
 627        INIT_HLIST_HEAD(&blkcg->blkg_list);
 628
 629        return &blkcg->css;
 630}
 631
 632/**
 633 * blkcg_init_queue - initialize blkcg part of request queue
 634 * @q: request_queue to initialize
 635 *
 636 * Called from blk_alloc_queue_node(). Responsible for initializing blkcg
 637 * part of new request_queue @q.
 638 *
 639 * RETURNS:
 640 * 0 on success, -errno on failure.
 641 */
 642int blkcg_init_queue(struct request_queue *q)
 643{
 644        might_sleep();
 645
 646        return blk_throtl_init(q);
 647}
 648
 649/**
 650 * blkcg_drain_queue - drain blkcg part of request_queue
 651 * @q: request_queue to drain
 652 *
 653 * Called from blk_drain_queue().  Responsible for draining blkcg part.
 654 */
 655void blkcg_drain_queue(struct request_queue *q)
 656{
 657        lockdep_assert_held(q->queue_lock);
 658
 659        blk_throtl_drain(q);
 660}
 661
 662/**
 663 * blkcg_exit_queue - exit and release blkcg part of request_queue
 664 * @q: request_queue being released
 665 *
 666 * Called from blk_release_queue().  Responsible for exiting blkcg part.
 667 */
 668void blkcg_exit_queue(struct request_queue *q)
 669{
 670        spin_lock_irq(q->queue_lock);
 671        blkg_destroy_all(q);
 672        spin_unlock_irq(q->queue_lock);
 673
 674        blk_throtl_exit(q);
 675}
 676
 677/*
 678 * We cannot support shared io contexts, as we have no mean to support
 679 * two tasks with the same ioc in two different groups without major rework
 680 * of the main cic data structures.  For now we allow a task to change
 681 * its cgroup only if it's the only owner of its ioc.
 682 */
 683static int blkcg_can_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
 684{
 685        struct task_struct *task;
 686        struct io_context *ioc;
 687        int ret = 0;
 688
 689        /* task_lock() is needed to avoid races with exit_io_context() */
 690        cgroup_taskset_for_each(task, cgrp, tset) {
 691                task_lock(task);
 692                ioc = task->io_context;
 693                if (ioc && atomic_read(&ioc->nr_tasks) > 1)
 694                        ret = -EINVAL;
 695                task_unlock(task);
 696                if (ret)
 697                        break;
 698        }
 699        return ret;
 700}
 701
 702struct cgroup_subsys blkio_subsys = {
 703        .name = "blkio",
 704        .create = blkcg_create,
 705        .can_attach = blkcg_can_attach,
 706        .pre_destroy = blkcg_pre_destroy,
 707        .destroy = blkcg_destroy,
 708        .subsys_id = blkio_subsys_id,
 709        .base_cftypes = blkcg_files,
 710        .module = THIS_MODULE,
 711};
 712EXPORT_SYMBOL_GPL(blkio_subsys);
 713
 714/**
 715 * blkcg_activate_policy - activate a blkcg policy on a request_queue
 716 * @q: request_queue of interest
 717 * @pol: blkcg policy to activate
 718 *
 719 * Activate @pol on @q.  Requires %GFP_KERNEL context.  @q goes through
 720 * bypass mode to populate its blkgs with policy_data for @pol.
 721 *
 722 * Activation happens with @q bypassed, so nobody would be accessing blkgs
 723 * from IO path.  Update of each blkg is protected by both queue and blkcg
 724 * locks so that holding either lock and testing blkcg_policy_enabled() is
 725 * always enough for dereferencing policy data.
 726 *
 727 * The caller is responsible for synchronizing [de]activations and policy
 728 * [un]registerations.  Returns 0 on success, -errno on failure.
 729 */
 730int blkcg_activate_policy(struct request_queue *q,
 731                          const struct blkcg_policy *pol)
 732{
 733        LIST_HEAD(pds);
 734        struct blkcg_gq *blkg;
 735        struct blkg_policy_data *pd, *n;
 736        int cnt = 0, ret;
 737
 738        if (blkcg_policy_enabled(q, pol))
 739                return 0;
 740
 741        blk_queue_bypass_start(q);
 742
 743        /* make sure the root blkg exists and count the existing blkgs */
 744        spin_lock_irq(q->queue_lock);
 745
 746        rcu_read_lock();
 747        blkg = __blkg_lookup_create(&blkcg_root, q);
 748        rcu_read_unlock();
 749
 750        if (IS_ERR(blkg)) {
 751                ret = PTR_ERR(blkg);
 752                goto out_unlock;
 753        }
 754        q->root_blkg = blkg;
 755
 756        list_for_each_entry(blkg, &q->blkg_list, q_node)
 757                cnt++;
 758
 759        spin_unlock_irq(q->queue_lock);
 760
 761        /* allocate policy_data for all existing blkgs */
 762        while (cnt--) {
 763                pd = kzalloc_node(pol->pd_size, GFP_KERNEL, q->node);
 764                if (!pd) {
 765                        ret = -ENOMEM;
 766                        goto out_free;
 767                }
 768                list_add_tail(&pd->alloc_node, &pds);
 769        }
 770
 771        /*
 772         * Install the allocated pds.  With @q bypassing, no new blkg
 773         * should have been created while the queue lock was dropped.
 774         */
 775        spin_lock_irq(q->queue_lock);
 776
 777        list_for_each_entry(blkg, &q->blkg_list, q_node) {
 778                if (WARN_ON(list_empty(&pds))) {
 779                        /* umm... this shouldn't happen, just abort */
 780                        ret = -ENOMEM;
 781                        goto out_unlock;
 782                }
 783                pd = list_first_entry(&pds, struct blkg_policy_data, alloc_node);
 784                list_del_init(&pd->alloc_node);
 785
 786                /* grab blkcg lock too while installing @pd on @blkg */
 787                spin_lock(&blkg->blkcg->lock);
 788
 789                blkg->pd[pol->plid] = pd;
 790                pd->blkg = blkg;
 791                pol->pd_init_fn(blkg);
 792
 793                spin_unlock(&blkg->blkcg->lock);
 794        }
 795
 796        __set_bit(pol->plid, q->blkcg_pols);
 797        ret = 0;
 798out_unlock:
 799        spin_unlock_irq(q->queue_lock);
 800out_free:
 801        blk_queue_bypass_end(q);
 802        list_for_each_entry_safe(pd, n, &pds, alloc_node)
 803                kfree(pd);
 804        return ret;
 805}
 806EXPORT_SYMBOL_GPL(blkcg_activate_policy);
 807
 808/**
 809 * blkcg_deactivate_policy - deactivate a blkcg policy on a request_queue
 810 * @q: request_queue of interest
 811 * @pol: blkcg policy to deactivate
 812 *
 813 * Deactivate @pol on @q.  Follows the same synchronization rules as
 814 * blkcg_activate_policy().
 815 */
 816void blkcg_deactivate_policy(struct request_queue *q,
 817                             const struct blkcg_policy *pol)
 818{
 819        struct blkcg_gq *blkg;
 820
 821        if (!blkcg_policy_enabled(q, pol))
 822                return;
 823
 824        blk_queue_bypass_start(q);
 825        spin_lock_irq(q->queue_lock);
 826
 827        __clear_bit(pol->plid, q->blkcg_pols);
 828
 829        /* if no policy is left, no need for blkgs - shoot them down */
 830        if (bitmap_empty(q->blkcg_pols, BLKCG_MAX_POLS))
 831                blkg_destroy_all(q);
 832
 833        list_for_each_entry(blkg, &q->blkg_list, q_node) {
 834                /* grab blkcg lock too while removing @pd from @blkg */
 835                spin_lock(&blkg->blkcg->lock);
 836
 837                if (pol->pd_exit_fn)
 838                        pol->pd_exit_fn(blkg);
 839
 840                kfree(blkg->pd[pol->plid]);
 841                blkg->pd[pol->plid] = NULL;
 842
 843                spin_unlock(&blkg->blkcg->lock);
 844        }
 845
 846        spin_unlock_irq(q->queue_lock);
 847        blk_queue_bypass_end(q);
 848}
 849EXPORT_SYMBOL_GPL(blkcg_deactivate_policy);
 850
 851/**
 852 * blkcg_policy_register - register a blkcg policy
 853 * @pol: blkcg policy to register
 854 *
 855 * Register @pol with blkcg core.  Might sleep and @pol may be modified on
 856 * successful registration.  Returns 0 on success and -errno on failure.
 857 */
 858int blkcg_policy_register(struct blkcg_policy *pol)
 859{
 860        int i, ret;
 861
 862        if (WARN_ON(pol->pd_size < sizeof(struct blkg_policy_data)))
 863                return -EINVAL;
 864
 865        mutex_lock(&blkcg_pol_mutex);
 866
 867        /* find an empty slot */
 868        ret = -ENOSPC;
 869        for (i = 0; i < BLKCG_MAX_POLS; i++)
 870                if (!blkcg_policy[i])
 871                        break;
 872        if (i >= BLKCG_MAX_POLS)
 873                goto out_unlock;
 874
 875        /* register and update blkgs */
 876        pol->plid = i;
 877        blkcg_policy[i] = pol;
 878
 879        /* everything is in place, add intf files for the new policy */
 880        if (pol->cftypes)
 881                WARN_ON(cgroup_add_cftypes(&blkio_subsys, pol->cftypes));
 882        ret = 0;
 883out_unlock:
 884        mutex_unlock(&blkcg_pol_mutex);
 885        return ret;
 886}
 887EXPORT_SYMBOL_GPL(blkcg_policy_register);
 888
 889/**
 890 * blkcg_policy_unregister - unregister a blkcg policy
 891 * @pol: blkcg policy to unregister
 892 *
 893 * Undo blkcg_policy_register(@pol).  Might sleep.
 894 */
 895void blkcg_policy_unregister(struct blkcg_policy *pol)
 896{
 897        mutex_lock(&blkcg_pol_mutex);
 898
 899        if (WARN_ON(blkcg_policy[pol->plid] != pol))
 900                goto out_unlock;
 901
 902        /* kill the intf files first */
 903        if (pol->cftypes)
 904                cgroup_rm_cftypes(&blkio_subsys, pol->cftypes);
 905
 906        /* unregister and update blkgs */
 907        blkcg_policy[pol->plid] = NULL;
 908out_unlock:
 909        mutex_unlock(&blkcg_pol_mutex);
 910}
 911EXPORT_SYMBOL_GPL(blkcg_policy_unregister);
 912
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