mm/backing-dev.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2
   3 #include <linux/wait.h>
   4 #include <linux/rbtree.h>
   5 #include <linux/backing-dev.h>
   6 #include <linux/kthread.h>
   7 #include <linux/freezer.h>
   8 #include <linux/fs.h>
   9 #include <linux/pagemap.h>
  10 #include <linux/mm.h>
  11 #include <linux/sched/mm.h>
  12 #include <linux/sched.h>
  13 #include <linux/module.h>
  14 #include <linux/writeback.h>
  15 #include <linux/device.h>
  16 #include <trace/events/writeback.h>
  17
  18 struct backing_dev_info noop_backing_dev_info;
  19 EXPORT_SYMBOL_GPL(noop_backing_dev_info);
  20
  21 static struct class *bdi_class;
  22 static const char *bdi_unknown_name = "(unknown)";
  23
  24 /*
  25  * bdi_lock protects bdi_tree and updates to bdi_list. bdi_list has RCU
  26  * reader side locking.
  27  */
  28 DEFINE_SPINLOCK(bdi_lock);
  29 static u64 bdi_id_cursor;
  30 static struct rb_root bdi_tree = RB_ROOT;
  31 LIST_HEAD(bdi_list);
  32
  33 /* bdi_wq serves all asynchronous writeback tasks */
  34 struct workqueue_struct *bdi_wq;
  35
  36 #define K(x) ((x) << (PAGE_SHIFT - 10))
  37
  38 #ifdef CONFIG_DEBUG_FS
  39 #include <linux/debugfs.h>
  40 #include <linux/seq_file.h>
  41
  42 static struct dentry *bdi_debug_root;
  43
  44 static void bdi_debug_init(void)
  45 {
  46         bdi_debug_root = debugfs_create_dir("bdi", NULL);
  47 }
  48
  49 static int bdi_debug_stats_show(struct seq_file *m, void *v)
  50 {
  51         struct backing_dev_info *bdi = m->private;
  52         struct bdi_writeback *wb = &bdi->wb;
  53         unsigned long background_thresh;
  54         unsigned long dirty_thresh;
  55         unsigned long wb_thresh;
  56         unsigned long nr_dirty, nr_io, nr_more_io, nr_dirty_time;
  57         struct inode *inode;
  58
  59         nr_dirty = nr_io = nr_more_io = nr_dirty_time = 0;
  60         spin_lock(&wb->list_lock);
  61         list_for_each_entry(inode, &wb->b_dirty, i_io_list)
  62                 nr_dirty++;
  63         list_for_each_entry(inode, &wb->b_io, i_io_list)
  64                 nr_io++;
  65         list_for_each_entry(inode, &wb->b_more_io, i_io_list)
  66                 nr_more_io++;
  67         list_for_each_entry(inode, &wb->b_dirty_time, i_io_list)
  68                 if (inode->i_state & I_DIRTY_TIME)
  69                         nr_dirty_time++;
  70         spin_unlock(&wb->list_lock);
  71
  72         global_dirty_limits(&background_thresh, &dirty_thresh);
  73         wb_thresh = wb_calc_thresh(wb, dirty_thresh);
  74
  75         seq_printf(m,
  76                    "BdiWriteback:       %10lu kB\n"
  77                    "BdiReclaimable:     %10lu kB\n"
  78                    "BdiDirtyThresh:     %10lu kB\n"
  79                    "DirtyThresh:        %10lu kB\n"
  80                    "BackgroundThresh:   %10lu kB\n"
  81                    "BdiDirtied:         %10lu kB\n"
  82                    "BdiWritten:         %10lu kB\n"
  83                    "BdiWriteBandwidth:  %10lu kBps\n"
  84                    "b_dirty:            %10lu\n"
  85                    "b_io:               %10lu\n"
  86                    "b_more_io:          %10lu\n"
  87                    "b_dirty_time:       %10lu\n"
  88                    "bdi_list:           %10u\n"
  89                    "state:              %10lx\n",
  90                    (unsigned long) K(wb_stat(wb, WB_WRITEBACK)),
  91                    (unsigned long) K(wb_stat(wb, WB_RECLAIMABLE)),
  92                    K(wb_thresh),
  93                    K(dirty_thresh),
  94                    K(background_thresh),
  95                    (unsigned long) K(wb_stat(wb, WB_DIRTIED)),
  96                    (unsigned long) K(wb_stat(wb, WB_WRITTEN)),
  97                    (unsigned long) K(wb->write_bandwidth),
  98                    nr_dirty,
  99                    nr_io,
 100                    nr_more_io,
 101                    nr_dirty_time,
 102                    !list_empty(&bdi->bdi_list), bdi->wb.state);
 103
 104         return 0;
 105 }
 106 DEFINE_SHOW_ATTRIBUTE(bdi_debug_stats);
 107
 108 static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
 109 {
 110         bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
 111
 112         debugfs_create_file("stats", 0444, bdi->debug_dir, bdi,
 113                             &bdi_debug_stats_fops);
 114 }
 115
 116 static void bdi_debug_unregister(struct backing_dev_info *bdi)
 117 {
 118         debugfs_remove_recursive(bdi->debug_dir);
 119 }
 120 #else
 121 static inline void bdi_debug_init(void)
 122 {
 123 }
 124 static inline void bdi_debug_register(struct backing_dev_info *bdi,
 125                                       const char *name)
 126 {
 127 }
 128 static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
 129 {
 130 }
 131 #endif
 132
 133 static ssize_t read_ahead_kb_store(struct device *dev,
 134                                   struct device_attribute *attr,
 135                                   const char *buf, size_t count)
 136 {
 137         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 138         unsigned long read_ahead_kb;
 139         ssize_t ret;
 140
 141         ret = kstrtoul(buf, 10, &read_ahead_kb);
 142         if (ret < 0)
 143                 return ret;
 144
 145         bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
 146
 147         return count;
 148 }
 149
 150 #define BDI_SHOW(name, expr)                                            \
 151 static ssize_t name##_show(struct device *dev,                          \
 152                            struct device_attribute *attr, char *buf)    \
 153 {                                                                       \
 154         struct backing_dev_info *bdi = dev_get_drvdata(dev);            \
 155                                                                         \
 156         return sysfs_emit(buf, "%lld\n", (long long)expr);              \
 157 }                                                                       \
 158 static DEVICE_ATTR_RW(name);
 159
 160 BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
 161
 162 static ssize_t min_ratio_store(struct device *dev,
 163                 struct device_attribute *attr, const char *buf, size_t count)
 164 {
 165         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 166         unsigned int ratio;
 167         ssize_t ret;
 168
 169         ret = kstrtouint(buf, 10, &ratio);
 170         if (ret < 0)
 171                 return ret;
 172
 173         ret = bdi_set_min_ratio(bdi, ratio);
 174         if (!ret)
 175                 ret = count;
 176
 177         return ret;
 178 }
 179 BDI_SHOW(min_ratio, bdi->min_ratio)
 180
 181 static ssize_t max_ratio_store(struct device *dev,
 182                 struct device_attribute *attr, const char *buf, size_t count)
 183 {
 184         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 185         unsigned int ratio;
 186         ssize_t ret;
 187
 188         ret = kstrtouint(buf, 10, &ratio);
 189         if (ret < 0)
 190                 return ret;
 191
 192         ret = bdi_set_max_ratio(bdi, ratio);
 193         if (!ret)
 194                 ret = count;
 195
 196         return ret;
 197 }
 198 BDI_SHOW(max_ratio, bdi->max_ratio)
 199
 200 static ssize_t stable_pages_required_show(struct device *dev,
 201                                           struct device_attribute *attr,
 202                                           char *buf)
 203 {
 204         dev_warn_once(dev,
 205                 "the stable_pages_required attribute has been removed. Use the stable_writes queue attribute instead.\n");
 206         return sysfs_emit(buf, "%d\n", 0);
 207 }
 208 static DEVICE_ATTR_RO(stable_pages_required);
 209
 210 static struct attribute *bdi_dev_attrs[] = {
 211         &dev_attr_read_ahead_kb.attr,
 212         &dev_attr_min_ratio.attr,
 213         &dev_attr_max_ratio.attr,
 214         &dev_attr_stable_pages_required.attr,
 215         NULL,
 216 };
 217 ATTRIBUTE_GROUPS(bdi_dev);
 218
 219 static __init int bdi_class_init(void)
 220 {
 221         bdi_class = class_create(THIS_MODULE, "bdi");
 222         if (IS_ERR(bdi_class))
 223                 return PTR_ERR(bdi_class);
 224
 225         bdi_class->dev_groups = bdi_dev_groups;
 226         bdi_debug_init();
 227
 228         return 0;
 229 }
 230 postcore_initcall(bdi_class_init);
 231
 232 static int bdi_init(struct backing_dev_info *bdi);
 233
 234 static int __init default_bdi_init(void)
 235 {
 236         int err;
 237
 238         bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_UNBOUND |
 239                                  WQ_SYSFS, 0);
 240         if (!bdi_wq)
 241                 return -ENOMEM;
 242
 243         err = bdi_init(&noop_backing_dev_info);
 244
 245         return err;
 246 }
 247 subsys_initcall(default_bdi_init);
 248
 249 /*
 250  * This function is used when the first inode for this wb is marked dirty. It
 251  * wakes-up the corresponding bdi thread which should then take care of the
 252  * periodic background write-out of dirty inodes. Since the write-out would
 253  * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
 254  * set up a timer which wakes the bdi thread up later.
 255  *
 256  * Note, we wouldn't bother setting up the timer, but this function is on the
 257  * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
 258  * by delaying the wake-up.
 259  *
 260  * We have to be careful not to postpone flush work if it is scheduled for
 261  * earlier. Thus we use queue_delayed_work().
 262  */
 263 void wb_wakeup_delayed(struct bdi_writeback *wb)
 264 {
 265         unsigned long timeout;
 266
 267         timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
 268         spin_lock_bh(&wb->work_lock);
 269         if (test_bit(WB_registered, &wb->state))
 270                 queue_delayed_work(bdi_wq, &wb->dwork, timeout);
 271         spin_unlock_bh(&wb->work_lock);
 272 }
 273
 274 /*
 275  * Initial write bandwidth: 100 MB/s
 276  */
 277 #define INIT_BW         (100 << (20 - PAGE_SHIFT))
 278
 279 static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
 280                    gfp_t gfp)
 281 {
 282         int i, err;
 283
 284         memset(wb, 0, sizeof(*wb));
 285
 286         if (wb != &bdi->wb)
 287                 bdi_get(bdi);
 288         wb->bdi = bdi;
 289         wb->last_old_flush = jiffies;
 290         INIT_LIST_HEAD(&wb->b_dirty);
 291         INIT_LIST_HEAD(&wb->b_io);
 292         INIT_LIST_HEAD(&wb->b_more_io);
 293         INIT_LIST_HEAD(&wb->b_dirty_time);
 294         spin_lock_init(&wb->list_lock);
 295
 296         wb->bw_time_stamp = jiffies;
 297         wb->balanced_dirty_ratelimit = INIT_BW;
 298         wb->dirty_ratelimit = INIT_BW;
 299         wb->write_bandwidth = INIT_BW;
 300         wb->avg_write_bandwidth = INIT_BW;
 301
 302         spin_lock_init(&wb->work_lock);
 303         INIT_LIST_HEAD(&wb->work_list);
 304         INIT_DELAYED_WORK(&wb->dwork, wb_workfn);
 305         wb->dirty_sleep = jiffies;
 306
 307         err = fprop_local_init_percpu(&wb->completions, gfp);
 308         if (err)
 309                 goto out_put_bdi;
 310
 311         for (i = 0; i < NR_WB_STAT_ITEMS; i++) {
 312                 err = percpu_counter_init(&wb->stat[i], 0, gfp);
 313                 if (err)
 314                         goto out_destroy_stat;
 315         }
 316
 317         return 0;
 318
 319 out_destroy_stat:
 320         while (i--)
 321                 percpu_counter_destroy(&wb->stat[i]);
 322         fprop_local_destroy_percpu(&wb->completions);
 323 out_put_bdi:
 324         if (wb != &bdi->wb)
 325                 bdi_put(bdi);
 326         return err;
 327 }
 328
 329 static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb);
 330
 331 /*
 332  * Remove bdi from the global list and shutdown any threads we have running
 333  */
 334 static void wb_shutdown(struct bdi_writeback *wb)
 335 {
 336         /* Make sure nobody queues further work */
 337         spin_lock_bh(&wb->work_lock);
 338         if (!test_and_clear_bit(WB_registered, &wb->state)) {
 339                 spin_unlock_bh(&wb->work_lock);
 340                 return;
 341         }
 342         spin_unlock_bh(&wb->work_lock);
 343
 344         cgwb_remove_from_bdi_list(wb);
 345         /*
 346          * Drain work list and shutdown the delayed_work.  !WB_registered
 347          * tells wb_workfn() that @wb is dying and its work_list needs to
 348          * be drained no matter what.
 349          */
 350         mod_delayed_work(bdi_wq, &wb->dwork, 0);
 351         flush_delayed_work(&wb->dwork);
 352         WARN_ON(!list_empty(&wb->work_list));
 353 }
 354
 355 static void wb_exit(struct bdi_writeback *wb)
 356 {
 357         int i;
 358
 359         WARN_ON(delayed_work_pending(&wb->dwork));
 360
 361         for (i = 0; i < NR_WB_STAT_ITEMS; i++)
 362                 percpu_counter_destroy(&wb->stat[i]);
 363
 364         fprop_local_destroy_percpu(&wb->completions);
 365         if (wb != &wb->bdi->wb)
 366                 bdi_put(wb->bdi);
 367 }
 368
 369 #ifdef CONFIG_CGROUP_WRITEBACK
 370
 371 #include <linux/memcontrol.h>
 372
 373 /*
 374  * cgwb_lock protects bdi->cgwb_tree, blkcg->cgwb_list, offline_cgwbs and
 375  * memcg->cgwb_list.  bdi->cgwb_tree is also RCU protected.
 376  */
 377 static DEFINE_SPINLOCK(cgwb_lock);
 378 static struct workqueue_struct *cgwb_release_wq;
 379
 380 static LIST_HEAD(offline_cgwbs);
 381 static void cleanup_offline_cgwbs_workfn(struct work_struct *work);
 382 static DECLARE_WORK(cleanup_offline_cgwbs_work, cleanup_offline_cgwbs_workfn);
 383
 384 static void cgwb_release_workfn(struct work_struct *work)
 385 {
 386         struct bdi_writeback *wb = container_of(work, struct bdi_writeback,
 387                                                 release_work);
 388         struct blkcg *blkcg = css_to_blkcg(wb->blkcg_css);
 389
 390         mutex_lock(&wb->bdi->cgwb_release_mutex);
 391         wb_shutdown(wb);
 392
 393         css_put(wb->memcg_css);
 394         css_put(wb->blkcg_css);
 395         mutex_unlock(&wb->bdi->cgwb_release_mutex);
 396
 397         /* triggers blkg destruction if no online users left */
 398         blkcg_unpin_online(blkcg);
 399
 400         fprop_local_destroy_percpu(&wb->memcg_completions);
 401
 402         spin_lock_irq(&cgwb_lock);
 403         list_del(&wb->offline_node);
 404         spin_unlock_irq(&cgwb_lock);
 405
 406         percpu_ref_exit(&wb->refcnt);
 407         wb_exit(wb);
 408         WARN_ON_ONCE(!list_empty(&wb->b_attached));
 409         kfree_rcu(wb, rcu);
 410 }
 411
 412 static void cgwb_release(struct percpu_ref *refcnt)
 413 {
 414         struct bdi_writeback *wb = container_of(refcnt, struct bdi_writeback,
 415                                                 refcnt);
 416         queue_work(cgwb_release_wq, &wb->release_work);
 417 }
 418
 419 static void cgwb_kill(struct bdi_writeback *wb)
 420 {
 421         lockdep_assert_held(&cgwb_lock);
 422
 423         WARN_ON(!radix_tree_delete(&wb->bdi->cgwb_tree, wb->memcg_css->id));
 424         list_del(&wb->memcg_node);
 425         list_del(&wb->blkcg_node);
 426         list_add(&wb->offline_node, &offline_cgwbs);
 427         percpu_ref_kill(&wb->refcnt);
 428 }
 429
 430 static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb)
 431 {
 432         spin_lock_irq(&cgwb_lock);
 433         list_del_rcu(&wb->bdi_node);
 434         spin_unlock_irq(&cgwb_lock);
 435 }
 436
 437 static int cgwb_create(struct backing_dev_info *bdi,
 438                        struct cgroup_subsys_state *memcg_css, gfp_t gfp)
 439 {
 440         struct mem_cgroup *memcg;
 441         struct cgroup_subsys_state *blkcg_css;
 442         struct blkcg *blkcg;
 443         struct list_head *memcg_cgwb_list, *blkcg_cgwb_list;
 444         struct bdi_writeback *wb;
 445         unsigned long flags;
 446         int ret = 0;
 447
 448         memcg = mem_cgroup_from_css(memcg_css);
 449         blkcg_css = cgroup_get_e_css(memcg_css->cgroup, &io_cgrp_subsys);
 450         blkcg = css_to_blkcg(blkcg_css);
 451         memcg_cgwb_list = &memcg->cgwb_list;
 452         blkcg_cgwb_list = &blkcg->cgwb_list;
 453
 454         /* look up again under lock and discard on blkcg mismatch */
 455         spin_lock_irqsave(&cgwb_lock, flags);
 456         wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
 457         if (wb && wb->blkcg_css != blkcg_css) {
 458                 cgwb_kill(wb);
 459                 wb = NULL;
 460         }
 461         spin_unlock_irqrestore(&cgwb_lock, flags);
 462         if (wb)
 463                 goto out_put;
 464
 465         /* need to create a new one */
 466         wb = kmalloc(sizeof(*wb), gfp);
 467         if (!wb) {
 468                 ret = -ENOMEM;
 469                 goto out_put;
 470         }
 471
 472         ret = wb_init(wb, bdi, gfp);
 473         if (ret)
 474                 goto err_free;
 475
 476         ret = percpu_ref_init(&wb->refcnt, cgwb_release, 0, gfp);
 477         if (ret)
 478                 goto err_wb_exit;
 479
 480         ret = fprop_local_init_percpu(&wb->memcg_completions, gfp);
 481         if (ret)
 482                 goto err_ref_exit;
 483
 484         wb->memcg_css = memcg_css;
 485         wb->blkcg_css = blkcg_css;
 486         INIT_LIST_HEAD(&wb->b_attached);
 487         INIT_WORK(&wb->release_work, cgwb_release_workfn);
 488         set_bit(WB_registered, &wb->state);
 489
 490         /*
 491          * The root wb determines the registered state of the whole bdi and
 492          * memcg_cgwb_list and blkcg_cgwb_list's next pointers indicate
 493          * whether they're still online.  Don't link @wb if any is dead.
 494          * See wb_memcg_offline() and wb_blkcg_offline().
 495          */
 496         ret = -ENODEV;
 497         spin_lock_irqsave(&cgwb_lock, flags);
 498         if (test_bit(WB_registered, &bdi->wb.state) &&
 499             blkcg_cgwb_list->next && memcg_cgwb_list->next) {
 500                 /* we might have raced another instance of this function */
 501                 ret = radix_tree_insert(&bdi->cgwb_tree, memcg_css->id, wb);
 502                 if (!ret) {
 503                         list_add_tail_rcu(&wb->bdi_node, &bdi->wb_list);
 504                         list_add(&wb->memcg_node, memcg_cgwb_list);
 505                         list_add(&wb->blkcg_node, blkcg_cgwb_list);
 506                         blkcg_pin_online(blkcg);
 507                         css_get(memcg_css);
 508                         css_get(blkcg_css);
 509                 }
 510         }
 511         spin_unlock_irqrestore(&cgwb_lock, flags);
 512         if (ret) {
 513                 if (ret == -EEXIST)
 514                         ret = 0;
 515                 goto err_fprop_exit;
 516         }
 517         goto out_put;
 518
 519 err_fprop_exit:
 520         fprop_local_destroy_percpu(&wb->memcg_completions);
 521 err_ref_exit:
 522         percpu_ref_exit(&wb->refcnt);
 523 err_wb_exit:
 524         wb_exit(wb);
 525 err_free:
 526         kfree(wb);
 527 out_put:
 528         css_put(blkcg_css);
 529         return ret;
 530 }
 531
 532 /**
 533  * wb_get_lookup - get wb for a given memcg
 534  * @bdi: target bdi
 535  * @memcg_css: cgroup_subsys_state of the target memcg (must have positive ref)
 536  *
 537  * Try to get the wb for @memcg_css on @bdi.  The returned wb has its
 538  * refcount incremented.
 539  *
 540  * This function uses css_get() on @memcg_css and thus expects its refcnt
 541  * to be positive on invocation.  IOW, rcu_read_lock() protection on
 542  * @memcg_css isn't enough.  try_get it before calling this function.
 543  *
 544  * A wb is keyed by its associated memcg.  As blkcg implicitly enables
 545  * memcg on the default hierarchy, memcg association is guaranteed to be
 546  * more specific (equal or descendant to the associated blkcg) and thus can
 547  * identify both the memcg and blkcg associations.
 548  *
 549  * Because the blkcg associated with a memcg may change as blkcg is enabled
 550  * and disabled closer to root in the hierarchy, each wb keeps track of
 551  * both the memcg and blkcg associated with it and verifies the blkcg on
 552  * each lookup.  On mismatch, the existing wb is discarded and a new one is
 553  * created.
 554  */
 555 struct bdi_writeback *wb_get_lookup(struct backing_dev_info *bdi,
 556                                     struct cgroup_subsys_state *memcg_css)
 557 {
 558         struct bdi_writeback *wb;
 559
 560         if (!memcg_css->parent)
 561                 return &bdi->wb;
 562
 563         rcu_read_lock();
 564         wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
 565         if (wb) {
 566                 struct cgroup_subsys_state *blkcg_css;
 567
 568                 /* see whether the blkcg association has changed */
 569                 blkcg_css = cgroup_get_e_css(memcg_css->cgroup, &io_cgrp_subsys);
 570                 if (unlikely(wb->blkcg_css != blkcg_css || !wb_tryget(wb)))
 571                         wb = NULL;
 572                 css_put(blkcg_css);
 573         }
 574         rcu_read_unlock();
 575
 576         return wb;
 577 }
 578
 579 /**
 580  * wb_get_create - get wb for a given memcg, create if necessary
 581  * @bdi: target bdi
 582  * @memcg_css: cgroup_subsys_state of the target memcg (must have positive ref)
 583  * @gfp: allocation mask to use
 584  *
 585  * Try to get the wb for @memcg_css on @bdi.  If it doesn't exist, try to
 586  * create one.  See wb_get_lookup() for more details.
 587  */
 588 struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
 589                                     struct cgroup_subsys_state *memcg_css,
 590                                     gfp_t gfp)
 591 {
 592         struct bdi_writeback *wb;
 593
 594         might_alloc(gfp);
 595
 596         if (!memcg_css->parent)
 597                 return &bdi->wb;
 598
 599         do {
 600                 wb = wb_get_lookup(bdi, memcg_css);
 601         } while (!wb && !cgwb_create(bdi, memcg_css, gfp));
 602
 603         return wb;
 604 }
 605
 606 static int cgwb_bdi_init(struct backing_dev_info *bdi)
 607 {
 608         int ret;
 609
 610         INIT_RADIX_TREE(&bdi->cgwb_tree, GFP_ATOMIC);
 611         mutex_init(&bdi->cgwb_release_mutex);
 612         init_rwsem(&bdi->wb_switch_rwsem);
 613
 614         ret = wb_init(&bdi->wb, bdi, GFP_KERNEL);
 615         if (!ret) {
 616                 bdi->wb.memcg_css = &root_mem_cgroup->css;
 617                 bdi->wb.blkcg_css = blkcg_root_css;
 618         }
 619         return ret;
 620 }
 621
 622 static void cgwb_bdi_unregister(struct backing_dev_info *bdi)
 623 {
 624         struct radix_tree_iter iter;
 625         void **slot;
 626         struct bdi_writeback *wb;
 627
 628         WARN_ON(test_bit(WB_registered, &bdi->wb.state));
 629
 630         spin_lock_irq(&cgwb_lock);
 631         radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
 632                 cgwb_kill(*slot);
 633         spin_unlock_irq(&cgwb_lock);
 634
 635         mutex_lock(&bdi->cgwb_release_mutex);
 636         spin_lock_irq(&cgwb_lock);
 637         while (!list_empty(&bdi->wb_list)) {
 638                 wb = list_first_entry(&bdi->wb_list, struct bdi_writeback,
 639                                       bdi_node);
 640                 spin_unlock_irq(&cgwb_lock);
 641                 wb_shutdown(wb);
 642                 spin_lock_irq(&cgwb_lock);
 643         }
 644         spin_unlock_irq(&cgwb_lock);
 645         mutex_unlock(&bdi->cgwb_release_mutex);
 646 }
 647
 648 /*
 649  * cleanup_offline_cgwbs_workfn - try to release dying cgwbs
 650  *
 651  * Try to release dying cgwbs by switching attached inodes to the nearest
 652  * living ancestor's writeback. Processed wbs are placed at the end
 653  * of the list to guarantee the forward progress.
 654  */
 655 static void cleanup_offline_cgwbs_workfn(struct work_struct *work)
 656 {
 657         struct bdi_writeback *wb;
 658         LIST_HEAD(processed);
 659
 660         spin_lock_irq(&cgwb_lock);
 661
 662         while (!list_empty(&offline_cgwbs)) {
 663                 wb = list_first_entry(&offline_cgwbs, struct bdi_writeback,
 664                                       offline_node);
 665                 list_move(&wb->offline_node, &processed);
 666
 667                 /*
 668                  * If wb is dirty, cleaning up the writeback by switching
 669                  * attached inodes will result in an effective removal of any
 670                  * bandwidth restrictions, which isn't the goal.  Instead,
 671                  * it can be postponed until the next time, when all io
 672                  * will be likely completed.  If in the meantime some inodes
 673                  * will get re-dirtied, they should be eventually switched to
 674                  * a new cgwb.
 675                  */
 676                 if (wb_has_dirty_io(wb))
 677                         continue;
 678
 679                 if (!wb_tryget(wb))
 680                         continue;
 681
 682                 spin_unlock_irq(&cgwb_lock);
 683                 while (cleanup_offline_cgwb(wb))
 684                         cond_resched();
 685                 spin_lock_irq(&cgwb_lock);
 686
 687                 wb_put(wb);
 688         }
 689
 690         if (!list_empty(&processed))
 691                 list_splice_tail(&processed, &offline_cgwbs);
 692
 693         spin_unlock_irq(&cgwb_lock);
 694 }
 695
 696 /**
 697  * wb_memcg_offline - kill all wb's associated with a memcg being offlined
 698  * @memcg: memcg being offlined
 699  *
 700  * Also prevents creation of any new wb's associated with @memcg.
 701  */
 702 void wb_memcg_offline(struct mem_cgroup *memcg)
 703 {
 704         struct list_head *memcg_cgwb_list = &memcg->cgwb_list;
 705         struct bdi_writeback *wb, *next;
 706
 707         spin_lock_irq(&cgwb_lock);
 708         list_for_each_entry_safe(wb, next, memcg_cgwb_list, memcg_node)
 709                 cgwb_kill(wb);
 710         memcg_cgwb_list->next = NULL;   /* prevent new wb's */
 711         spin_unlock_irq(&cgwb_lock);
 712
 713         queue_work(system_unbound_wq, &cleanup_offline_cgwbs_work);
 714 }
 715
 716 /**
 717  * wb_blkcg_offline - kill all wb's associated with a blkcg being offlined
 718  * @blkcg: blkcg being offlined
 719  *
 720  * Also prevents creation of any new wb's associated with @blkcg.
 721  */
 722 void wb_blkcg_offline(struct blkcg *blkcg)
 723 {
 724         struct bdi_writeback *wb, *next;
 725
 726         spin_lock_irq(&cgwb_lock);
 727         list_for_each_entry_safe(wb, next, &blkcg->cgwb_list, blkcg_node)
 728                 cgwb_kill(wb);
 729         blkcg->cgwb_list.next = NULL;   /* prevent new wb's */
 730         spin_unlock_irq(&cgwb_lock);
 731 }
 732
 733 static void cgwb_bdi_register(struct backing_dev_info *bdi)
 734 {
 735         spin_lock_irq(&cgwb_lock);
 736         list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
 737         spin_unlock_irq(&cgwb_lock);
 738 }
 739
 740 static int __init cgwb_init(void)
 741 {
 742         /*
 743          * There can be many concurrent release work items overwhelming
 744          * system_wq.  Put them in a separate wq and limit concurrency.
 745          * There's no point in executing many of these in parallel.
 746          */
 747         cgwb_release_wq = alloc_workqueue("cgwb_release", 0, 1);
 748         if (!cgwb_release_wq)
 749                 return -ENOMEM;
 750
 751         return 0;
 752 }
 753 subsys_initcall(cgwb_init);
 754
 755 #else   /* CONFIG_CGROUP_WRITEBACK */
 756
 757 static int cgwb_bdi_init(struct backing_dev_info *bdi)
 758 {
 759         return wb_init(&bdi->wb, bdi, GFP_KERNEL);
 760 }
 761
 762 static void cgwb_bdi_unregister(struct backing_dev_info *bdi) { }
 763
 764 static void cgwb_bdi_register(struct backing_dev_info *bdi)
 765 {
 766         list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
 767 }
 768
 769 static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb)
 770 {
 771         list_del_rcu(&wb->bdi_node);
 772 }
 773
 774 #endif  /* CONFIG_CGROUP_WRITEBACK */
 775
 776 static int bdi_init(struct backing_dev_info *bdi)
 777 {
 778         int ret;
 779
 780         bdi->dev = NULL;
 781
 782         kref_init(&bdi->refcnt);
 783         bdi->min_ratio = 0;
 784         bdi->max_ratio = 100;
 785         bdi->max_prop_frac = FPROP_FRAC_BASE;
 786         INIT_LIST_HEAD(&bdi->bdi_list);
 787         INIT_LIST_HEAD(&bdi->wb_list);
 788         init_waitqueue_head(&bdi->wb_waitq);
 789
 790         ret = cgwb_bdi_init(bdi);
 791
 792         return ret;
 793 }
 794
 795 struct backing_dev_info *bdi_alloc(int node_id)
 796 {
 797         struct backing_dev_info *bdi;
 798
 799         bdi = kzalloc_node(sizeof(*bdi), GFP_KERNEL, node_id);
 800         if (!bdi)
 801                 return NULL;
 802
 803         if (bdi_init(bdi)) {
 804                 kfree(bdi);
 805                 return NULL;
 806         }
 807         bdi->capabilities = BDI_CAP_WRITEBACK | BDI_CAP_WRITEBACK_ACCT;
 808         bdi->ra_pages = VM_READAHEAD_PAGES;
 809         bdi->io_pages = VM_READAHEAD_PAGES;
 810         return bdi;
 811 }
 812 EXPORT_SYMBOL(bdi_alloc);
 813
 814 static struct rb_node **bdi_lookup_rb_node(u64 id, struct rb_node **parentp)
 815 {
 816         struct rb_node **p = &bdi_tree.rb_node;
 817         struct rb_node *parent = NULL;
 818         struct backing_dev_info *bdi;
 819
 820         lockdep_assert_held(&bdi_lock);
 821
 822         while (*p) {
 823                 parent = *p;
 824                 bdi = rb_entry(parent, struct backing_dev_info, rb_node);
 825
 826                 if (bdi->id > id)
 827                         p = &(*p)->rb_left;
 828                 else if (bdi->id < id)
 829                         p = &(*p)->rb_right;
 830                 else
 831                         break;
 832         }
 833
 834         if (parentp)
 835                 *parentp = parent;
 836         return p;
 837 }
 838
 839 /**
 840  * bdi_get_by_id - lookup and get bdi from its id
 841  * @id: bdi id to lookup
 842  *
 843  * Find bdi matching @id and get it.  Returns NULL if the matching bdi
 844  * doesn't exist or is already unregistered.
 845  */
 846 struct backing_dev_info *bdi_get_by_id(u64 id)
 847 {
 848         struct backing_dev_info *bdi = NULL;
 849         struct rb_node **p;
 850
 851         spin_lock_bh(&bdi_lock);
 852         p = bdi_lookup_rb_node(id, NULL);
 853         if (*p) {
 854                 bdi = rb_entry(*p, struct backing_dev_info, rb_node);
 855                 bdi_get(bdi);
 856         }
 857         spin_unlock_bh(&bdi_lock);
 858
 859         return bdi;
 860 }
 861
 862 int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args)
 863 {
 864         struct device *dev;
 865         struct rb_node *parent, **p;
 866
 867         if (bdi->dev)   /* The driver needs to use separate queues per device */
 868                 return 0;
 869
 870         vsnprintf(bdi->dev_name, sizeof(bdi->dev_name), fmt, args);
 871         dev = device_create(bdi_class, NULL, MKDEV(0, 0), bdi, bdi->dev_name);
 872         if (IS_ERR(dev))
 873                 return PTR_ERR(dev);
 874
 875         cgwb_bdi_register(bdi);
 876         bdi->dev = dev;
 877
 878         bdi_debug_register(bdi, dev_name(dev));
 879         set_bit(WB_registered, &bdi->wb.state);
 880
 881         spin_lock_bh(&bdi_lock);
 882
 883         bdi->id = ++bdi_id_cursor;
 884
 885         p = bdi_lookup_rb_node(bdi->id, &parent);
 886         rb_link_node(&bdi->rb_node, parent, p);
 887         rb_insert_color(&bdi->rb_node, &bdi_tree);
 888
 889         list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
 890
 891         spin_unlock_bh(&bdi_lock);
 892
 893         trace_writeback_bdi_register(bdi);
 894         return 0;
 895 }
 896
 897 int bdi_register(struct backing_dev_info *bdi, const char *fmt, ...)
 898 {
 899         va_list args;
 900         int ret;
 901
 902         va_start(args, fmt);
 903         ret = bdi_register_va(bdi, fmt, args);
 904         va_end(args);
 905         return ret;
 906 }
 907 EXPORT_SYMBOL(bdi_register);
 908
 909 void bdi_set_owner(struct backing_dev_info *bdi, struct device *owner)
 910 {
 911         WARN_ON_ONCE(bdi->owner);
 912         bdi->owner = owner;
 913         get_device(owner);
 914 }
 915
 916 /*
 917  * Remove bdi from bdi_list, and ensure that it is no longer visible
 918  */
 919 static void bdi_remove_from_list(struct backing_dev_info *bdi)
 920 {
 921         spin_lock_bh(&bdi_lock);
 922         rb_erase(&bdi->rb_node, &bdi_tree);
 923         list_del_rcu(&bdi->bdi_list);
 924         spin_unlock_bh(&bdi_lock);
 925
 926         synchronize_rcu_expedited();
 927 }
 928
 929 void bdi_unregister(struct backing_dev_info *bdi)
 930 {
 931         /* make sure nobody finds us on the bdi_list anymore */
 932         bdi_remove_from_list(bdi);
 933         wb_shutdown(&bdi->wb);
 934         cgwb_bdi_unregister(bdi);
 935
 936         if (bdi->dev) {
 937                 bdi_debug_unregister(bdi);
 938                 device_unregister(bdi->dev);
 939                 bdi->dev = NULL;
 940         }
 941
 942         if (bdi->owner) {
 943                 put_device(bdi->owner);
 944                 bdi->owner = NULL;
 945         }
 946 }
 947
 948 static void release_bdi(struct kref *ref)
 949 {
 950         struct backing_dev_info *bdi =
 951                         container_of(ref, struct backing_dev_info, refcnt);
 952
 953         if (test_bit(WB_registered, &bdi->wb.state))
 954                 bdi_unregister(bdi);
 955         WARN_ON_ONCE(bdi->dev);
 956         wb_exit(&bdi->wb);
 957         kfree(bdi);
 958 }
 959
 960 void bdi_put(struct backing_dev_info *bdi)
 961 {
 962         kref_put(&bdi->refcnt, release_bdi);
 963 }
 964 EXPORT_SYMBOL(bdi_put);
 965
 966 const char *bdi_dev_name(struct backing_dev_info *bdi)
 967 {
 968         if (!bdi || !bdi->dev)
 969                 return bdi_unknown_name;
 970         return bdi->dev_name;
 971 }
 972 EXPORT_SYMBOL_GPL(bdi_dev_name);
 973
 974 static wait_queue_head_t congestion_wqh[2] = {
 975                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
 976                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
 977         };
 978 static atomic_t nr_wb_congested[2];
 979
 980 void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
 981 {
 982         wait_queue_head_t *wqh = &congestion_wqh[sync];
 983         enum wb_congested_state bit;
 984
 985         bit = sync ? WB_sync_congested : WB_async_congested;
 986         if (test_and_clear_bit(bit, &bdi->wb.congested))
 987                 atomic_dec(&nr_wb_congested[sync]);
 988         smp_mb__after_atomic();
 989         if (waitqueue_active(wqh))
 990                 wake_up(wqh);
 991 }
 992 EXPORT_SYMBOL(clear_bdi_congested);
 993
 994 void set_bdi_congested(struct backing_dev_info *bdi, int sync)
 995 {
 996         enum wb_congested_state bit;
 997
 998         bit = sync ? WB_sync_congested : WB_async_congested;
 999         if (!test_and_set_bit(bit, &bdi->wb.congested))
1000                 atomic_inc(&nr_wb_congested[sync]);
1001 }
1002 EXPORT_SYMBOL(set_bdi_congested);
1003
1004 /**
1005  * congestion_wait - wait for a backing_dev to become uncongested
1006  * @sync: SYNC or ASYNC IO
1007  * @timeout: timeout in jiffies
1008  *
1009  * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
1010  * write congestion.  If no backing_devs are congested then just wait for the
1011  * next write to be completed.
1012  */
1013 long congestion_wait(int sync, long timeout)
1014 {
1015         long ret;
1016         unsigned long start = jiffies;
1017         DEFINE_WAIT(wait);
1018         wait_queue_head_t *wqh = &congestion_wqh[sync];
1019
1020         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1021         ret = io_schedule_timeout(timeout);
1022         finish_wait(wqh, &wait);
1023
1024         trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
1025                                         jiffies_to_usecs(jiffies - start));
1026
1027         return ret;
1028 }
1029 EXPORT_SYMBOL(congestion_wait);
1030
1031 /**
1032  * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a pgdat to complete writes
1033  * @sync: SYNC or ASYNC IO
1034  * @timeout: timeout in jiffies
1035  *
1036  * In the event of a congested backing_dev (any backing_dev) this waits
1037  * for up to @timeout jiffies for either a BDI to exit congestion of the
1038  * given @sync queue or a write to complete.
1039  *
1040  * The return value is 0 if the sleep is for the full timeout. Otherwise,
1041  * it is the number of jiffies that were still remaining when the function
1042  * returned. return_value == timeout implies the function did not sleep.
1043  */
1044 long wait_iff_congested(int sync, long timeout)
1045 {
1046         long ret;
1047         unsigned long start = jiffies;
1048         DEFINE_WAIT(wait);
1049         wait_queue_head_t *wqh = &congestion_wqh[sync];
1050
1051         /*
1052          * If there is no congestion, yield if necessary instead
1053          * of sleeping on the congestion queue
1054          */
1055         if (atomic_read(&nr_wb_congested[sync]) == 0) {
1056                 cond_resched();
1057
1058                 /* In case we scheduled, work out time remaining */
1059                 ret = timeout - (jiffies - start);
1060                 if (ret < 0)
1061                         ret = 0;
1062
1063                 goto out;
1064         }
1065
1066         /* Sleep until uncongested or a write happens */
1067         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1068         ret = io_schedule_timeout(timeout);
1069         finish_wait(wqh, &wait);
1070
1071 out:
1072         trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
1073                                         jiffies_to_usecs(jiffies - start));
1074
1075         return ret;
1076 }
1077 EXPORT_SYMBOL(wait_iff_congested);