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
  34static bool blkcg_policy_enabled(struct request_queue *q,
  35                                 const struct blkcg_policy *pol)
  36{
  37        return pol && test_bit(pol->plid, q->blkcg_pols);
  38}
  39
  40/**
  41 * blkg_free - free a blkg
  42 * @blkg: blkg to free
  43 *
  44 * Free @blkg which may be partially allocated.
  45 */
  46static void blkg_free(struct blkcg_gq *blkg)
  47{
  48        int i;
  49
  50        if (!blkg)
  51                return;
  52
  53        for (i = 0; i < BLKCG_MAX_POLS; i++) {
  54                struct blkcg_policy *pol = blkcg_policy[i];
  55                struct blkg_policy_data *pd = blkg->pd[i];
  56
  57                if (!pd)
  58                        continue;
  59
  60                if (pol && pol->pd_exit_fn)
  61                        pol->pd_exit_fn(blkg);
  62
  63                kfree(pd);
  64        }
  65
  66        blk_exit_rl(&blkg->rl);
  67        kfree(blkg);
  68}
  69
  70/**
  71 * blkg_alloc - allocate a blkg
  72 * @blkcg: block cgroup the new blkg is associated with
  73 * @q: request_queue the new blkg is associated with
  74 * @gfp_mask: allocation mask to use
  75 *
  76 * Allocate a new blkg assocating @blkcg and @q.
  77 */
  78static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
  79                                   gfp_t gfp_mask)
  80{
  81        struct blkcg_gq *blkg;
  82        int i;
  83
  84        /* alloc and init base part */
  85        blkg = kzalloc_node(sizeof(*blkg), gfp_mask, q->node);
  86        if (!blkg)
  87                return NULL;
  88
  89        blkg->q = q;
  90        INIT_LIST_HEAD(&blkg->q_node);
  91        blkg->blkcg = blkcg;
  92        blkg->refcnt = 1;
  93
  94        /* root blkg uses @q->root_rl, init rl only for !root blkgs */
  95        if (blkcg != &blkcg_root) {
  96                if (blk_init_rl(&blkg->rl, q, gfp_mask))
  97                        goto err_free;
  98                blkg->rl.blkg = blkg;
  99        }
 100
 101        for (i = 0; i < BLKCG_MAX_POLS; i++) {
 102                struct blkcg_policy *pol = blkcg_policy[i];
 103                struct blkg_policy_data *pd;
 104
 105                if (!blkcg_policy_enabled(q, pol))
 106                        continue;
 107
 108                /* alloc per-policy data and attach it to blkg */
 109                pd = kzalloc_node(pol->pd_size, gfp_mask, q->node);
 110                if (!pd)
 111                        goto err_free;
 112
 113                blkg->pd[i] = pd;
 114                pd->blkg = blkg;
 115
 116                /* invoke per-policy init */
 117                if (blkcg_policy_enabled(blkg->q, pol))
 118                        pol->pd_init_fn(blkg);
 119        }
 120
 121        return blkg;
 122
 123err_free:
 124        blkg_free(blkg);
 125        return NULL;
 126}
 127
 128static struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg,
 129                                      struct request_queue *q)
 130{
 131        struct blkcg_gq *blkg;
 132
 133        blkg = rcu_dereference(blkcg->blkg_hint);
 134        if (blkg && blkg->q == q)
 135                return blkg;
 136
 137        /*
 138         * Hint didn't match.  Look up from the radix tree.  Note that we
 139         * may not be holding queue_lock and thus are not sure whether
 140         * @blkg from blkg_tree has already been removed or not, so we
 141         * can't update hint to the lookup result.  Leave it to the caller.
 142         */
 143        blkg = radix_tree_lookup(&blkcg->blkg_tree, q->id);
 144        if (blkg && blkg->q == q)
 145                return blkg;
 146
 147        return NULL;
 148}
 149
 150/**
 151 * blkg_lookup - lookup blkg for the specified blkcg - q pair
 152 * @blkcg: blkcg of interest
 153 * @q: request_queue of interest
 154 *
 155 * Lookup blkg for the @blkcg - @q pair.  This function should be called
 156 * under RCU read lock and is guaranteed to return %NULL if @q is bypassing
 157 * - see blk_queue_bypass_start() for details.
 158 */
 159struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, struct request_queue *q)
 160{
 161        WARN_ON_ONCE(!rcu_read_lock_held());
 162
 163        if (unlikely(blk_queue_bypass(q)))
 164                return NULL;
 165        return __blkg_lookup(blkcg, q);
 166}
 167EXPORT_SYMBOL_GPL(blkg_lookup);
 168
 169/*
 170 * If @new_blkg is %NULL, this function tries to allocate a new one as
 171 * necessary using %GFP_ATOMIC.  @new_blkg is always consumed on return.
 172 */
 173static struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
 174                                             struct request_queue *q,
 175                                             struct blkcg_gq *new_blkg)
 176{
 177        struct blkcg_gq *blkg;
 178        int ret;
 179
 180        WARN_ON_ONCE(!rcu_read_lock_held());
 181        lockdep_assert_held(q->queue_lock);
 182
 183        /* lookup and update hint on success, see __blkg_lookup() for details */
 184        blkg = __blkg_lookup(blkcg, q);
 185        if (blkg) {
 186                rcu_assign_pointer(blkcg->blkg_hint, blkg);
 187                goto out_free;
 188        }
 189
 190        /* blkg holds a reference to blkcg */
 191        if (!css_tryget(&blkcg->css)) {
 192                blkg = ERR_PTR(-EINVAL);
 193                goto out_free;
 194        }
 195
 196        /* allocate */
 197        if (!new_blkg) {
 198                new_blkg = blkg_alloc(blkcg, q, GFP_ATOMIC);
 199                if (unlikely(!new_blkg)) {
 200                        blkg = ERR_PTR(-ENOMEM);
 201                        goto out_put;
 202                }
 203        }
 204        blkg = new_blkg;
 205
 206        /* insert */
 207        spin_lock(&blkcg->lock);
 208        ret = radix_tree_insert(&blkcg->blkg_tree, q->id, blkg);
 209        if (likely(!ret)) {
 210                hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
 211                list_add(&blkg->q_node, &q->blkg_list);
 212        }
 213        spin_unlock(&blkcg->lock);
 214
 215        if (!ret)
 216                return blkg;
 217
 218        blkg = ERR_PTR(ret);
 219out_put:
 220        css_put(&blkcg->css);
 221out_free:
 222        blkg_free(new_blkg);
 223        return blkg;
 224}
 225
 226struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
 227                                    struct request_queue *q)
 228{
 229        /*
 230         * This could be the first entry point of blkcg implementation and
 231         * we shouldn't allow anything to go through for a bypassing queue.
 232         */
 233        if (unlikely(blk_queue_bypass(q)))
 234                return ERR_PTR(blk_queue_dead(q) ? -EINVAL : -EBUSY);
 235        return __blkg_lookup_create(blkcg, q, NULL);
 236}
 237EXPORT_SYMBOL_GPL(blkg_lookup_create);
 238
 239static void blkg_destroy(struct blkcg_gq *blkg)
 240{
 241        struct blkcg *blkcg = blkg->blkcg;
 242
 243        lockdep_assert_held(blkg->q->queue_lock);
 244        lockdep_assert_held(&blkcg->lock);
 245
 246        /* Something wrong if we are trying to remove same group twice */
 247        WARN_ON_ONCE(list_empty(&blkg->q_node));
 248        WARN_ON_ONCE(hlist_unhashed(&blkg->blkcg_node));
 249
 250        radix_tree_delete(&blkcg->blkg_tree, blkg->q->id);
 251        list_del_init(&blkg->q_node);
 252        hlist_del_init_rcu(&blkg->blkcg_node);
 253
 254        /*
 255         * Both setting lookup hint to and clearing it from @blkg are done
 256         * under queue_lock.  If it's not pointing to @blkg now, it never
 257         * will.  Hint assignment itself can race safely.
 258         */
 259        if (rcu_dereference_raw(blkcg->blkg_hint) == blkg)
 260                rcu_assign_pointer(blkcg->blkg_hint, NULL);
 261
 262        /*
 263         * Put the reference taken at the time of creation so that when all
 264         * queues are gone, group can be destroyed.
 265         */
 266        blkg_put(blkg);
 267}
 268
 269/**
 270 * blkg_destroy_all - destroy all blkgs associated with a request_queue
 271 * @q: request_queue of interest
 272 *
 273 * Destroy all blkgs associated with @q.
 274 */
 275static void blkg_destroy_all(struct request_queue *q)
 276{
 277        struct blkcg_gq *blkg, *n;
 278
 279        lockdep_assert_held(q->queue_lock);
 280
 281        list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
 282                struct blkcg *blkcg = blkg->blkcg;
 283
 284                spin_lock(&blkcg->lock);
 285                blkg_destroy(blkg);
 286                spin_unlock(&blkcg->lock);
 287        }
 288}
 289
 290static void blkg_rcu_free(struct rcu_head *rcu_head)
 291{
 292        blkg_free(container_of(rcu_head, struct blkcg_gq, rcu_head));
 293}
 294
 295void __blkg_release(struct blkcg_gq *blkg)
 296{
 297        /* release the extra blkcg reference this blkg has been holding */
 298        css_put(&blkg->blkcg->css);
 299
 300        /*
 301         * A group is freed in rcu manner. But having an rcu lock does not
 302         * mean that one can access all the fields of blkg and assume these
 303         * are valid. For example, don't try to follow throtl_data and
 304         * request queue links.
 305         *
 306         * Having a reference to blkg under an rcu allows acess to only
 307         * values local to groups like group stats and group rate limits
 308         */
 309        call_rcu(&blkg->rcu_head, blkg_rcu_free);
 310}
 311EXPORT_SYMBOL_GPL(__blkg_release);
 312
 313/*
 314 * The next function used by blk_queue_for_each_rl().  It's a bit tricky
 315 * because the root blkg uses @q->root_rl instead of its own rl.
 316 */
 317struct request_list *__blk_queue_next_rl(struct request_list *rl,
 318                                         struct request_queue *q)
 319{
 320        struct list_head *ent;
 321        struct blkcg_gq *blkg;
 322
 323        /*
 324         * Determine the current blkg list_head.  The first entry is
 325         * root_rl which is off @q->blkg_list and mapped to the head.
 326         */
 327        if (rl == &q->root_rl) {
 328                ent = &q->blkg_list;
 329        } else {
 330                blkg = container_of(rl, struct blkcg_gq, rl);
 331                ent = &blkg->q_node;
 332        }
 333
 334        /* walk to the next list_head, skip root blkcg */
 335        ent = ent->next;
 336        if (ent == &q->root_blkg->q_node)
 337                ent = ent->next;
 338        if (ent == &q->blkg_list)
 339                return NULL;
 340
 341        blkg = container_of(ent, struct blkcg_gq, q_node);
 342        return &blkg->rl;
 343}
 344
 345static int blkcg_reset_stats(struct cgroup *cgroup, struct cftype *cftype,
 346                             u64 val)
 347{
 348        struct blkcg *blkcg = cgroup_to_blkcg(cgroup);
 349        struct blkcg_gq *blkg;
 350        struct hlist_node *n;
 351        int i;
 352
 353        mutex_lock(&blkcg_pol_mutex);
 354        spin_lock_irq(&blkcg->lock);
 355
 356        /*
 357         * Note that stat reset is racy - it doesn't synchronize against
 358         * stat updates.  This is a debug feature which shouldn't exist
 359         * anyway.  If you get hit by a race, retry.
 360         */
 361        hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
 362                for (i = 0; i < BLKCG_MAX_POLS; i++) {
 363                        struct blkcg_policy *pol = blkcg_policy[i];
 364
 365                        if (blkcg_policy_enabled(blkg->q, pol) &&
 366                            pol->pd_reset_stats_fn)
 367                                pol->pd_reset_stats_fn(blkg);
 368                }
 369        }
 370
 371        spin_unlock_irq(&blkcg->lock);
 372        mutex_unlock(&blkcg_pol_mutex);
 373        return 0;
 374}
 375
 376static const char *blkg_dev_name(struct blkcg_gq *blkg)
 377{
 378        /* some drivers (floppy) instantiate a queue w/o disk registered */
 379        if (blkg->q->backing_dev_info.dev)
 380                return dev_name(blkg->q->backing_dev_info.dev);
 381        return NULL;
 382}
 383
 384/**
 385 * blkcg_print_blkgs - helper for printing per-blkg data
 386 * @sf: seq_file to print to
 387 * @blkcg: blkcg of interest
 388 * @prfill: fill function to print out a blkg
 389 * @pol: policy in question
 390 * @data: data to be passed to @prfill
 391 * @show_total: to print out sum of prfill return values or not
 392 *
 393 * This function invokes @prfill on each blkg of @blkcg if pd for the
 394 * policy specified by @pol exists.  @prfill is invoked with @sf, the
 395 * policy data and @data.  If @show_total is %true, the sum of the return
 396 * values from @prfill is printed with "Total" label at the end.
 397 *
 398 * This is to be used to construct print functions for
 399 * cftype->read_seq_string method.
 400 */
 401void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
 402                       u64 (*prfill)(struct seq_file *,
 403                                     struct blkg_policy_data *, int),
 404                       const struct blkcg_policy *pol, int data,
 405                       bool show_total)
 406{
 407        struct blkcg_gq *blkg;
 408        struct hlist_node *n;
 409        u64 total = 0;
 410
 411        spin_lock_irq(&blkcg->lock);
 412        hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node)
 413                if (blkcg_policy_enabled(blkg->q, pol))
 414                        total += prfill(sf, blkg->pd[pol->plid], data);
 415        spin_unlock_irq(&blkcg->lock);
 416
 417        if (show_total)
 418                seq_printf(sf, "Total %llu\n", (unsigned long long)total);
 419}
 420EXPORT_SYMBOL_GPL(blkcg_print_blkgs);
 421
 422/**
 423 * __blkg_prfill_u64 - prfill helper for a single u64 value
 424 * @sf: seq_file to print to
 425 * @pd: policy private data of interest
 426 * @v: value to print
 427 *
 428 * Print @v to @sf for the device assocaited with @pd.
 429 */
 430u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v)
 431{
 432        const char *dname = blkg_dev_name(pd->blkg);
 433
 434        if (!dname)
 435                return 0;
 436
 437        seq_printf(sf, "%s %llu\n", dname, (unsigned long long)v);
 438        return v;
 439}
 440EXPORT_SYMBOL_GPL(__blkg_prfill_u64);
 441
 442/**
 443 * __blkg_prfill_rwstat - prfill helper for a blkg_rwstat
 444 * @sf: seq_file to print to
 445 * @pd: policy private data of interest
 446 * @rwstat: rwstat to print
 447 *
 448 * Print @rwstat to @sf for the device assocaited with @pd.
 449 */
 450u64 __blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
 451                         const struct blkg_rwstat *rwstat)
 452{
 453        static const char *rwstr[] = {
 454                [BLKG_RWSTAT_READ]      = "Read",
 455                [BLKG_RWSTAT_WRITE]     = "Write",
 456                [BLKG_RWSTAT_SYNC]      = "Sync",
 457                [BLKG_RWSTAT_ASYNC]     = "Async",
 458        };
 459        const char *dname = blkg_dev_name(pd->blkg);
 460        u64 v;
 461        int i;
 462
 463        if (!dname)
 464                return 0;
 465
 466        for (i = 0; i < BLKG_RWSTAT_NR; i++)
 467                seq_printf(sf, "%s %s %llu\n", dname, rwstr[i],
 468                           (unsigned long long)rwstat->cnt[i]);
 469
 470        v = rwstat->cnt[BLKG_RWSTAT_READ] + rwstat->cnt[BLKG_RWSTAT_WRITE];
 471        seq_printf(sf, "%s Total %llu\n", dname, (unsigned long long)v);
 472        return v;
 473}
 474
 475/**
 476 * blkg_prfill_stat - prfill callback for blkg_stat
 477 * @sf: seq_file to print to
 478 * @pd: policy private data of interest
 479 * @off: offset to the blkg_stat in @pd
 480 *
 481 * prfill callback for printing a blkg_stat.
 482 */
 483u64 blkg_prfill_stat(struct seq_file *sf, struct blkg_policy_data *pd, int off)
 484{
 485        return __blkg_prfill_u64(sf, pd, blkg_stat_read((void *)pd + off));
 486}
 487EXPORT_SYMBOL_GPL(blkg_prfill_stat);
 488
 489/**
 490 * blkg_prfill_rwstat - prfill callback for blkg_rwstat
 491 * @sf: seq_file to print to
 492 * @pd: policy private data of interest
 493 * @off: offset to the blkg_rwstat in @pd
 494 *
 495 * prfill callback for printing a blkg_rwstat.
 496 */
 497u64 blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
 498                       int off)
 499{
 500        struct blkg_rwstat rwstat = blkg_rwstat_read((void *)pd + off);
 501
 502        return __blkg_prfill_rwstat(sf, pd, &rwstat);
 503}
 504EXPORT_SYMBOL_GPL(blkg_prfill_rwstat);
 505
 506/**
 507 * blkg_conf_prep - parse and prepare for per-blkg config update
 508 * @blkcg: target block cgroup
 509 * @pol: target policy
 510 * @input: input string
 511 * @ctx: blkg_conf_ctx to be filled
 512 *
 513 * Parse per-blkg config update from @input and initialize @ctx with the
 514 * result.  @ctx->blkg points to the blkg to be updated and @ctx->v the new
 515 * value.  This function returns with RCU read lock and queue lock held and
 516 * must be paired with blkg_conf_finish().
 517 */
 518int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 519                   const char *input, struct blkg_conf_ctx *ctx)
 520        __acquires(rcu) __acquires(disk->queue->queue_lock)
 521{
 522        struct gendisk *disk;
 523        struct blkcg_gq *blkg;
 524        unsigned int major, minor;
 525        unsigned long long v;
 526        int part, ret;
 527
 528        if (sscanf(input, "%u:%u %llu", &major, &minor, &v) != 3)
 529                return -EINVAL;
 530
 531        disk = get_gendisk(MKDEV(major, minor), &part);
 532        if (!disk || part)
 533                return -EINVAL;
 534
 535        rcu_read_lock();
 536        spin_lock_irq(disk->queue->queue_lock);
 537
 538        if (blkcg_policy_enabled(disk->queue, pol))
 539                blkg = blkg_lookup_create(blkcg, disk->queue);
 540        else
 541                blkg = ERR_PTR(-EINVAL);
 542
 543        if (IS_ERR(blkg)) {
 544                ret = PTR_ERR(blkg);
 545                rcu_read_unlock();
 546                spin_unlock_irq(disk->queue->queue_lock);
 547                put_disk(disk);
 548                /*
 549                 * If queue was bypassing, we should retry.  Do so after a
 550                 * short msleep().  It isn't strictly necessary but queue
 551                 * can be bypassing for some time and it's always nice to
 552                 * avoid busy looping.
 553                 */
 554                if (ret == -EBUSY) {
 555                        msleep(10);
 556                        ret = restart_syscall();
 557                }
 558                return ret;
 559        }
 560
 561        ctx->disk = disk;
 562        ctx->blkg = blkg;
 563        ctx->v = v;
 564        return 0;
 565}
 566EXPORT_SYMBOL_GPL(blkg_conf_prep);
 567
 568/**
 569 * blkg_conf_finish - finish up per-blkg config update
 570 * @ctx: blkg_conf_ctx intiailized by blkg_conf_prep()
 571 *
 572 * Finish up after per-blkg config update.  This function must be paired
 573 * with blkg_conf_prep().
 574 */
 575void blkg_conf_finish(struct blkg_conf_ctx *ctx)
 576        __releases(ctx->disk->queue->queue_lock) __releases(rcu)
 577{
 578        spin_unlock_irq(ctx->disk->queue->queue_lock);
 579        rcu_read_unlock();
 580        put_disk(ctx->disk);
 581}
 582EXPORT_SYMBOL_GPL(blkg_conf_finish);
 583
 584struct cftype blkcg_files[] = {
 585        {
 586                .name = "reset_stats",
 587                .write_u64 = blkcg_reset_stats,
 588        },
 589        { }     /* terminate */
 590};
 591
 592/**
 593 * blkcg_pre_destroy - cgroup pre_destroy callback
 594 * @cgroup: cgroup of interest
 595 *
 596 * This function is called when @cgroup is about to go away and responsible
 597 * for shooting down all blkgs associated with @cgroup.  blkgs should be
 598 * removed while holding both q and blkcg locks.  As blkcg lock is nested
 599 * inside q lock, this function performs reverse double lock dancing.
 600 *
 601 * This is the blkcg counterpart of ioc_release_fn().
 602 */
 603static int blkcg_pre_destroy(struct cgroup *cgroup)
 604{
 605        struct blkcg *blkcg = cgroup_to_blkcg(cgroup);
 606
 607        spin_lock_irq(&blkcg->lock);
 608
 609        while (!hlist_empty(&blkcg->blkg_list)) {
 610                struct blkcg_gq *blkg = hlist_entry(blkcg->blkg_list.first,
 611                                                struct blkcg_gq, blkcg_node);
 612                struct request_queue *q = blkg->q;
 613
 614                if (spin_trylock(q->queue_lock)) {
 615                        blkg_destroy(blkg);
 616                        spin_unlock(q->queue_lock);
 617                } else {
 618                        spin_unlock_irq(&blkcg->lock);
 619                        cpu_relax();
 620                        spin_lock_irq(&blkcg->lock);
 621                }
 622        }
 623
 624        spin_unlock_irq(&blkcg->lock);
 625        return 0;
 626}
 627
 628static void blkcg_destroy(struct cgroup *cgroup)
 629{
 630        struct blkcg *blkcg = cgroup_to_blkcg(cgroup);
 631
 632        if (blkcg != &blkcg_root)
 633                kfree(blkcg);
 634}
 635
 636static struct cgroup_subsys_state *blkcg_create(struct cgroup *cgroup)
 637{
 638        static atomic64_t id_seq = ATOMIC64_INIT(0);
 639        struct blkcg *blkcg;
 640        struct cgroup *parent = cgroup->parent;
 641
 642        if (!parent) {
 643                blkcg = &blkcg_root;
 644                goto done;
 645        }
 646
 647        blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL);
 648        if (!blkcg)
 649                return ERR_PTR(-ENOMEM);
 650
 651        blkcg->cfq_weight = CFQ_WEIGHT_DEFAULT;
 652        blkcg->id = atomic64_inc_return(&id_seq); /* root is 0, start from 1 */
 653done:
 654        spin_lock_init(&blkcg->lock);
 655        INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_ATOMIC);
 656        INIT_HLIST_HEAD(&blkcg->blkg_list);
 657
 658        return &blkcg->css;
 659}
 660
 661/**
 662 * blkcg_init_queue - initialize blkcg part of request queue
 663 * @q: request_queue to initialize
 664 *
 665 * Called from blk_alloc_queue_node(). Responsible for initializing blkcg
 666 * part of new request_queue @q.
 667 *
 668 * RETURNS:
 669 * 0 on success, -errno on failure.
 670 */
 671int blkcg_init_queue(struct request_queue *q)
 672{
 673        might_sleep();
 674
 675        return blk_throtl_init(q);
 676}
 677
 678/**
 679 * blkcg_drain_queue - drain blkcg part of request_queue
 680 * @q: request_queue to drain
 681 *
 682 * Called from blk_drain_queue().  Responsible for draining blkcg part.
 683 */
 684void blkcg_drain_queue(struct request_queue *q)
 685{
 686        lockdep_assert_held(q->queue_lock);
 687
 688        blk_throtl_drain(q);
 689}
 690
 691/**
 692 * blkcg_exit_queue - exit and release blkcg part of request_queue
 693 * @q: request_queue being released
 694 *
 695 * Called from blk_release_queue().  Responsible for exiting blkcg part.
 696 */
 697void blkcg_exit_queue(struct request_queue *q)
 698{
 699        spin_lock_irq(q->queue_lock);
 700        blkg_destroy_all(q);
 701        spin_unlock_irq(q->queue_lock);
 702
 703        blk_throtl_exit(q);
 704}
 705
 706/*
 707 * We cannot support shared io contexts, as we have no mean to support
 708 * two tasks with the same ioc in two different groups without major rework
 709 * of the main cic data structures.  For now we allow a task to change
 710 * its cgroup only if it's the only owner of its ioc.
 711 */
 712static int blkcg_can_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
 713{
 714        struct task_struct *task;
 715        struct io_context *ioc;
 716        int ret = 0;
 717
 718        /* task_lock() is needed to avoid races with exit_io_context() */
 719        cgroup_taskset_for_each(task, cgrp, tset) {
 720                task_lock(task);
 721                ioc = task->io_context;
 722                if (ioc && atomic_read(&ioc->nr_tasks) > 1)
 723                        ret = -EINVAL;
 724                task_unlock(task);
 725                if (ret)
 726                        break;
 727        }
 728        return ret;
 729}
 730
 731struct cgroup_subsys blkio_subsys = {
 732        .name = "blkio",
 733        .create = blkcg_create,
 734        .can_attach = blkcg_can_attach,
 735        .pre_destroy = blkcg_pre_destroy,
 736        .destroy = blkcg_destroy,
 737        .subsys_id = blkio_subsys_id,
 738        .base_cftypes = blkcg_files,
 739        .module = THIS_MODULE,
 740};
 741EXPORT_SYMBOL_GPL(blkio_subsys);
 742
 743/**
 744 * blkcg_activate_policy - activate a blkcg policy on a request_queue
 745 * @q: request_queue of interest
 746 * @pol: blkcg policy to activate
 747 *
 748 * Activate @pol on @q.  Requires %GFP_KERNEL context.  @q goes through
 749 * bypass mode to populate its blkgs with policy_data for @pol.
 750 *
 751 * Activation happens with @q bypassed, so nobody would be accessing blkgs
 752 * from IO path.  Update of each blkg is protected by both queue and blkcg
 753 * locks so that holding either lock and testing blkcg_policy_enabled() is
 754 * always enough for dereferencing policy data.
 755 *
 756 * The caller is responsible for synchronizing [de]activations and policy
 757 * [un]registerations.  Returns 0 on success, -errno on failure.
 758 */
 759int blkcg_activate_policy(struct request_queue *q,
 760                          const struct blkcg_policy *pol)
 761{
 762        LIST_HEAD(pds);
 763        struct blkcg_gq *blkg;
 764        struct blkg_policy_data *pd, *n;
 765        int cnt = 0, ret;
 766        bool preloaded;
 767
 768        if (blkcg_policy_enabled(q, pol))
 769                return 0;
 770
 771        /* preallocations for root blkg */
 772        blkg = blkg_alloc(&blkcg_root, q, GFP_KERNEL);
 773        if (!blkg)
 774                return -ENOMEM;
 775
 776        preloaded = !radix_tree_preload(GFP_KERNEL);
 777
 778        blk_queue_bypass_start(q);
 779
 780        /* make sure the root blkg exists and count the existing blkgs */
 781        spin_lock_irq(q->queue_lock);
 782
 783        rcu_read_lock();
 784        blkg = __blkg_lookup_create(&blkcg_root, q, blkg);
 785        rcu_read_unlock();
 786
 787        if (preloaded)
 788                radix_tree_preload_end();
 789
 790        if (IS_ERR(blkg)) {
 791                ret = PTR_ERR(blkg);
 792                goto out_unlock;
 793        }
 794        q->root_blkg = blkg;
 795        q->root_rl.blkg = blkg;
 796
 797        list_for_each_entry(blkg, &q->blkg_list, q_node)
 798                cnt++;
 799
 800        spin_unlock_irq(q->queue_lock);
 801
 802        /* allocate policy_data for all existing blkgs */
 803        while (cnt--) {
 804                pd = kzalloc_node(pol->pd_size, GFP_KERNEL, q->node);
 805                if (!pd) {
 806                        ret = -ENOMEM;
 807                        goto out_free;
 808                }
 809                list_add_tail(&pd->alloc_node, &pds);
 810        }
 811
 812        /*
 813         * Install the allocated pds.  With @q bypassing, no new blkg
 814         * should have been created while the queue lock was dropped.
 815         */
 816        spin_lock_irq(q->queue_lock);
 817
 818        list_for_each_entry(blkg, &q->blkg_list, q_node) {
 819                if (WARN_ON(list_empty(&pds))) {
 820                        /* umm... this shouldn't happen, just abort */
 821                        ret = -ENOMEM;
 822                        goto out_unlock;
 823                }
 824                pd = list_first_entry(&pds, struct blkg_policy_data, alloc_node);
 825                list_del_init(&pd->alloc_node);
 826
 827                /* grab blkcg lock too while installing @pd on @blkg */
 828                spin_lock(&blkg->blkcg->lock);
 829
 830                blkg->pd[pol->plid] = pd;
 831                pd->blkg = blkg;
 832                pol->pd_init_fn(blkg);
 833
 834                spin_unlock(&blkg->blkcg->lock);
 835        }
 836
 837        __set_bit(pol->plid, q->blkcg_pols);
 838        ret = 0;
 839out_unlock:
 840        spin_unlock_irq(q->queue_lock);
 841out_free:
 842        blk_queue_bypass_end(q);
 843        list_for_each_entry_safe(pd, n, &pds, alloc_node)
 844                kfree(pd);
 845        return ret;
 846}
 847EXPORT_SYMBOL_GPL(blkcg_activate_policy);
 848
 849/**
 850 * blkcg_deactivate_policy - deactivate a blkcg policy on a request_queue
 851 * @q: request_queue of interest
 852 * @pol: blkcg policy to deactivate
 853 *
 854 * Deactivate @pol on @q.  Follows the same synchronization rules as
 855 * blkcg_activate_policy().
 856 */
 857void blkcg_deactivate_policy(struct request_queue *q,
 858                             const struct blkcg_policy *pol)
 859{
 860        struct blkcg_gq *blkg;
 861
 862        if (!blkcg_policy_enabled(q, pol))
 863                return;
 864
 865        blk_queue_bypass_start(q);
 866        spin_lock_irq(q->queue_lock);
 867
 868        __clear_bit(pol->plid, q->blkcg_pols);
 869
 870        /* if no policy is left, no need for blkgs - shoot them down */
 871        if (bitmap_empty(q->blkcg_pols, BLKCG_MAX_POLS))
 872                blkg_destroy_all(q);
 873
 874        list_for_each_entry(blkg, &q->blkg_list, q_node) {
 875                /* grab blkcg lock too while removing @pd from @blkg */
 876                spin_lock(&blkg->blkcg->lock);
 877
 878                if (pol->pd_exit_fn)
 879                        pol->pd_exit_fn(blkg);
 880
 881                kfree(blkg->pd[pol->plid]);
 882                blkg->pd[pol->plid] = NULL;
 883
 884                spin_unlock(&blkg->blkcg->lock);
 885        }
 886
 887        spin_unlock_irq(q->queue_lock);
 888        blk_queue_bypass_end(q);
 889}
 890EXPORT_SYMBOL_GPL(blkcg_deactivate_policy);
 891
 892/**
 893 * blkcg_policy_register - register a blkcg policy
 894 * @pol: blkcg policy to register
 895 *
 896 * Register @pol with blkcg core.  Might sleep and @pol may be modified on
 897 * successful registration.  Returns 0 on success and -errno on failure.
 898 */
 899int blkcg_policy_register(struct blkcg_policy *pol)
 900{
 901        int i, ret;
 902
 903        if (WARN_ON(pol->pd_size < sizeof(struct blkg_policy_data)))
 904                return -EINVAL;
 905
 906        mutex_lock(&blkcg_pol_mutex);
 907
 908        /* find an empty slot */
 909        ret = -ENOSPC;
 910        for (i = 0; i < BLKCG_MAX_POLS; i++)
 911                if (!blkcg_policy[i])
 912                        break;
 913        if (i >= BLKCG_MAX_POLS)
 914                goto out_unlock;
 915
 916        /* register and update blkgs */
 917        pol->plid = i;
 918        blkcg_policy[i] = pol;
 919
 920        /* everything is in place, add intf files for the new policy */
 921        if (pol->cftypes)
 922                WARN_ON(cgroup_add_cftypes(&blkio_subsys, pol->cftypes));
 923        ret = 0;
 924out_unlock:
 925        mutex_unlock(&blkcg_pol_mutex);
 926        return ret;
 927}
 928EXPORT_SYMBOL_GPL(blkcg_policy_register);
 929
 930/**
 931 * blkcg_policy_unregister - unregister a blkcg policy
 932 * @pol: blkcg policy to unregister
 933 *
 934 * Undo blkcg_policy_register(@pol).  Might sleep.
 935 */
 936void blkcg_policy_unregister(struct blkcg_policy *pol)
 937{
 938        mutex_lock(&blkcg_pol_mutex);
 939
 940        if (WARN_ON(blkcg_policy[pol->plid] != pol))
 941                goto out_unlock;
 942
 943        /* kill the intf files first */
 944        if (pol->cftypes)
 945                cgroup_rm_cftypes(&blkio_subsys, pol->cftypes);
 946
 947        /* unregister and update blkgs */
 948        blkcg_policy[pol->plid] = NULL;
 949out_unlock:
 950        mutex_unlock(&blkcg_pol_mutex);
 951}
 952EXPORT_SYMBOL_GPL(blkcg_policy_unregister);
 953
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