// SPDX-License-Identifier: GPL-2.0-only

  
  #include <linux/wait.h>

  #include <linux/rbtree.h>

  #include <linux/backing-dev.h>

  #include <linux/kthread.h>
  #include <linux/freezer.h>

  #include <linux/fs.h>

  #include <linux/pagemap.h>

  #include <linux/mm.h>

  #include <linux/sched.h>
  #include <linux/module.h>

  #include <linux/writeback.h>
  #include <linux/device.h>

  #include <trace/events/writeback.h>

  struct backing_dev_info noop_backing_dev_info = {
  	.name		= "noop",

  	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,

  };

  EXPORT_SYMBOL_GPL(noop_backing_dev_info);

  static struct class *bdi_class;

  const char *bdi_unknown_name = "(unknown)";

  
  /*

   * bdi_lock protects bdi_tree and updates to bdi_list. bdi_list has RCU
   * reader side locking.

   */

  DEFINE_SPINLOCK(bdi_lock);

  static u64 bdi_id_cursor;
  static struct rb_root bdi_tree = RB_ROOT;

  LIST_HEAD(bdi_list);

  /* bdi_wq serves all asynchronous writeback tasks */
  struct workqueue_struct *bdi_wq;

  #ifdef CONFIG_DEBUG_FS
  #include <linux/debugfs.h>
  #include <linux/seq_file.h>
  
  static struct dentry *bdi_debug_root;
  
  static void bdi_debug_init(void)
  {
  	bdi_debug_root = debugfs_create_dir("bdi", NULL);
  }
  
  static int bdi_debug_stats_show(struct seq_file *m, void *v)
  {
  	struct backing_dev_info *bdi = m->private;

  	struct bdi_writeback *wb = &bdi->wb;

  	unsigned long background_thresh;
  	unsigned long dirty_thresh;

  	unsigned long wb_thresh;

  	unsigned long nr_dirty, nr_io, nr_more_io, nr_dirty_time;

  	struct inode *inode;

  	nr_dirty = nr_io = nr_more_io = nr_dirty_time = 0;

  	spin_lock(&wb->list_lock);

  	list_for_each_entry(inode, &wb->b_dirty, i_io_list)

  		nr_dirty++;

  	list_for_each_entry(inode, &wb->b_io, i_io_list)

  		nr_io++;

  	list_for_each_entry(inode, &wb->b_more_io, i_io_list)

  		nr_more_io++;

  	list_for_each_entry(inode, &wb->b_dirty_time, i_io_list)

  		if (inode->i_state & I_DIRTY_TIME)
  			nr_dirty_time++;

  	spin_unlock(&wb->list_lock);

  	global_dirty_limits(&background_thresh, &dirty_thresh);

  	wb_thresh = wb_calc_thresh(wb, dirty_thresh);

  
  #define K(x) ((x) << (PAGE_SHIFT - 10))
  	seq_printf(m,

  		   "BdiWriteback:       %10lu kB
  "
  		   "BdiReclaimable:     %10lu kB
  "
  		   "BdiDirtyThresh:     %10lu kB
  "
  		   "DirtyThresh:        %10lu kB
  "
  		   "BackgroundThresh:   %10lu kB
  "

  		   "BdiDirtied:         %10lu kB
  "

  		   "BdiWritten:         %10lu kB
  "
  		   "BdiWriteBandwidth:  %10lu kBps
  "
  		   "b_dirty:            %10lu
  "
  		   "b_io:               %10lu
  "
  		   "b_more_io:          %10lu
  "

  		   "b_dirty_time:       %10lu
  "

  		   "bdi_list:           %10u
  "
  		   "state:              %10lx
  ",

  		   (unsigned long) K(wb_stat(wb, WB_WRITEBACK)),
  		   (unsigned long) K(wb_stat(wb, WB_RECLAIMABLE)),

  		   K(wb_thresh),

  		   K(dirty_thresh),
  		   K(background_thresh),

  		   (unsigned long) K(wb_stat(wb, WB_DIRTIED)),
  		   (unsigned long) K(wb_stat(wb, WB_WRITTEN)),

  		   (unsigned long) K(wb->write_bandwidth),

  		   nr_dirty,
  		   nr_io,
  		   nr_more_io,

  		   nr_dirty_time,

  		   !list_empty(&bdi->bdi_list), bdi->wb.state);

  #undef K
  
  	return 0;
  }

  DEFINE_SHOW_ATTRIBUTE(bdi_debug_stats);

  static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)

  {
  	bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);

  	debugfs_create_file("stats", 0444, bdi->debug_dir, bdi,
  			    &bdi_debug_stats_fops);

  }
  
  static void bdi_debug_unregister(struct backing_dev_info *bdi)
  {

  	debugfs_remove_recursive(bdi->debug_dir);

  }
  #else
  static inline void bdi_debug_init(void)
  {
  }

  static inline void bdi_debug_register(struct backing_dev_info *bdi,

  				      const char *name)
  {
  }
  static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
  {
  }
  #endif

  static ssize_t read_ahead_kb_store(struct device *dev,
  				  struct device_attribute *attr,
  				  const char *buf, size_t count)
  {
  	struct backing_dev_info *bdi = dev_get_drvdata(dev);

  	unsigned long read_ahead_kb;

  	ssize_t ret;

  	ret = kstrtoul(buf, 10, &read_ahead_kb);
  	if (ret < 0)
  		return ret;
  
  	bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
  
  	return count;

  }
  
  #define K(pages) ((pages) << (PAGE_SHIFT - 10))
  
  #define BDI_SHOW(name, expr)						\
  static ssize_t name##_show(struct device *dev,				\
  			   struct device_attribute *attr, char *page)	\
  {									\
  	struct backing_dev_info *bdi = dev_get_drvdata(dev);		\
  									\
  	return snprintf(page, PAGE_SIZE-1, "%lld
  ", (long long)expr);	\

  }									\
  static DEVICE_ATTR_RW(name);

  
  BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))

  static ssize_t min_ratio_store(struct device *dev,
  		struct device_attribute *attr, const char *buf, size_t count)
  {
  	struct backing_dev_info *bdi = dev_get_drvdata(dev);

  	unsigned int ratio;

  	ssize_t ret;
  
  	ret = kstrtouint(buf, 10, &ratio);
  	if (ret < 0)
  		return ret;
  
  	ret = bdi_set_min_ratio(bdi, ratio);
  	if (!ret)
  		ret = count;

  	return ret;
  }
  BDI_SHOW(min_ratio, bdi->min_ratio)

  static ssize_t max_ratio_store(struct device *dev,
  		struct device_attribute *attr, const char *buf, size_t count)
  {
  	struct backing_dev_info *bdi = dev_get_drvdata(dev);

  	unsigned int ratio;

  	ssize_t ret;
  
  	ret = kstrtouint(buf, 10, &ratio);
  	if (ret < 0)
  		return ret;
  
  	ret = bdi_set_max_ratio(bdi, ratio);
  	if (!ret)
  		ret = count;

  	return ret;
  }
  BDI_SHOW(max_ratio, bdi->max_ratio)

  static ssize_t stable_pages_required_show(struct device *dev,
  					  struct device_attribute *attr,
  					  char *page)
  {
  	struct backing_dev_info *bdi = dev_get_drvdata(dev);
  
  	return snprintf(page, PAGE_SIZE-1, "%d
  ",
  			bdi_cap_stable_pages_required(bdi) ? 1 : 0);
  }

  static DEVICE_ATTR_RO(stable_pages_required);
  
  static struct attribute *bdi_dev_attrs[] = {
  	&dev_attr_read_ahead_kb.attr,
  	&dev_attr_min_ratio.attr,
  	&dev_attr_max_ratio.attr,
  	&dev_attr_stable_pages_required.attr,
  	NULL,

  };

  ATTRIBUTE_GROUPS(bdi_dev);

  
  static __init int bdi_class_init(void)
  {
  	bdi_class = class_create(THIS_MODULE, "bdi");

  	if (IS_ERR(bdi_class))
  		return PTR_ERR(bdi_class);

  	bdi_class->dev_groups = bdi_dev_groups;

  	bdi_debug_init();

  	return 0;
  }

  postcore_initcall(bdi_class_init);

  static int bdi_init(struct backing_dev_info *bdi);

  static int __init default_bdi_init(void)
  {
  	int err;

  	bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_UNBOUND |
  				 WQ_SYSFS, 0);

  	if (!bdi_wq)
  		return -ENOMEM;

  	err = bdi_init(&noop_backing_dev_info);

  
  	return err;
  }
  subsys_initcall(default_bdi_init);

  /*

   * This function is used when the first inode for this wb is marked dirty. It

   * wakes-up the corresponding bdi thread which should then take care of the
   * periodic background write-out of dirty inodes. Since the write-out would
   * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
   * set up a timer which wakes the bdi thread up later.
   *
   * Note, we wouldn't bother setting up the timer, but this function is on the
   * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
   * by delaying the wake-up.

   *
   * We have to be careful not to postpone flush work if it is scheduled for
   * earlier. Thus we use queue_delayed_work().

   */

  void wb_wakeup_delayed(struct bdi_writeback *wb)

  {
  	unsigned long timeout;
  
  	timeout = msecs_to_jiffies(dirty_writeback_interval * 10);

  	spin_lock_bh(&wb->work_lock);
  	if (test_bit(WB_registered, &wb->state))
  		queue_delayed_work(bdi_wq, &wb->dwork, timeout);
  	spin_unlock_bh(&wb->work_lock);

  }

  /*

   * Initial write bandwidth: 100 MB/s

   */

  #define INIT_BW		(100 << (20 - PAGE_SHIFT))

  static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,

  		   int blkcg_id, gfp_t gfp)

  {

  	int i, err;

  	memset(wb, 0, sizeof(*wb));

  	if (wb != &bdi->wb)
  		bdi_get(bdi);

  	wb->bdi = bdi;
  	wb->last_old_flush = jiffies;
  	INIT_LIST_HEAD(&wb->b_dirty);
  	INIT_LIST_HEAD(&wb->b_io);
  	INIT_LIST_HEAD(&wb->b_more_io);

  	INIT_LIST_HEAD(&wb->b_dirty_time);

  	spin_lock_init(&wb->list_lock);

  	wb->bw_time_stamp = jiffies;
  	wb->balanced_dirty_ratelimit = INIT_BW;
  	wb->dirty_ratelimit = INIT_BW;
  	wb->write_bandwidth = INIT_BW;
  	wb->avg_write_bandwidth = INIT_BW;

  	spin_lock_init(&wb->work_lock);
  	INIT_LIST_HEAD(&wb->work_list);
  	INIT_DELAYED_WORK(&wb->dwork, wb_workfn);

  	wb->dirty_sleep = jiffies;

  	wb->congested = wb_congested_get_create(bdi, blkcg_id, gfp);

  	if (!wb->congested) {
  		err = -ENOMEM;
  		goto out_put_bdi;
  	}

  	err = fprop_local_init_percpu(&wb->completions, gfp);

  	if (err)

  		goto out_put_cong;

  	for (i = 0; i < NR_WB_STAT_ITEMS; i++) {

  		err = percpu_counter_init(&wb->stat[i], 0, gfp);

  		if (err)
  			goto out_destroy_stat;

  	}

  	return 0;

  
  out_destroy_stat:

  	while (i--)

  		percpu_counter_destroy(&wb->stat[i]);
  	fprop_local_destroy_percpu(&wb->completions);
  out_put_cong:
  	wb_congested_put(wb->congested);

  out_put_bdi:
  	if (wb != &bdi->wb)
  		bdi_put(bdi);

  	return err;

  }

  static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb);

  /*
   * Remove bdi from the global list and shutdown any threads we have running
   */

  static void wb_shutdown(struct bdi_writeback *wb)

  {

  	/* Make sure nobody queues further work */

  	spin_lock_bh(&wb->work_lock);
  	if (!test_and_clear_bit(WB_registered, &wb->state)) {
  		spin_unlock_bh(&wb->work_lock);

  		return;

  	}

  	spin_unlock_bh(&wb->work_lock);

  	cgwb_remove_from_bdi_list(wb);

  	/*

  	 * Drain work list and shutdown the delayed_work.  !WB_registered
  	 * tells wb_workfn() that @wb is dying and its work_list needs to
  	 * be drained no matter what.

  	 */

  	mod_delayed_work(bdi_wq, &wb->dwork, 0);
  	flush_delayed_work(&wb->dwork);
  	WARN_ON(!list_empty(&wb->work_list));
  }

  static void wb_exit(struct bdi_writeback *wb)

  {
  	int i;
  
  	WARN_ON(delayed_work_pending(&wb->dwork));
  
  	for (i = 0; i < NR_WB_STAT_ITEMS; i++)
  		percpu_counter_destroy(&wb->stat[i]);

  	fprop_local_destroy_percpu(&wb->completions);

  	wb_congested_put(wb->congested);

  	if (wb != &wb->bdi->wb)
  		bdi_put(wb->bdi);

  }

  #ifdef CONFIG_CGROUP_WRITEBACK
  
  #include <linux/memcontrol.h>
  
  /*
   * cgwb_lock protects bdi->cgwb_tree, bdi->cgwb_congested_tree,
   * blkcg->cgwb_list, and memcg->cgwb_list.  bdi->cgwb_tree is also RCU

   * protected.

   */
  static DEFINE_SPINLOCK(cgwb_lock);

  static struct workqueue_struct *cgwb_release_wq;

  
  /**
   * wb_congested_get_create - get or create a wb_congested
   * @bdi: associated bdi
   * @blkcg_id: ID of the associated blkcg
   * @gfp: allocation mask
   *
   * Look up the wb_congested for @blkcg_id on @bdi.  If missing, create one.
   * The returned wb_congested has its reference count incremented.  Returns
   * NULL on failure.
   */
  struct bdi_writeback_congested *
  wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
  {
  	struct bdi_writeback_congested *new_congested = NULL, *congested;
  	struct rb_node **node, *parent;
  	unsigned long flags;

  retry:
  	spin_lock_irqsave(&cgwb_lock, flags);
  
  	node = &bdi->cgwb_congested_tree.rb_node;
  	parent = NULL;
  
  	while (*node != NULL) {
  		parent = *node;

  		congested = rb_entry(parent, struct bdi_writeback_congested,
  				     rb_node);

  		if (congested->blkcg_id < blkcg_id)
  			node = &parent->rb_left;
  		else if (congested->blkcg_id > blkcg_id)
  			node = &parent->rb_right;
  		else
  			goto found;
  	}
  
  	if (new_congested) {
  		/* !found and storage for new one already allocated, insert */
  		congested = new_congested;

  		rb_link_node(&congested->rb_node, parent, node);
  		rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree);

  		spin_unlock_irqrestore(&cgwb_lock, flags);
  		return congested;

  	}
  
  	spin_unlock_irqrestore(&cgwb_lock, flags);
  
  	/* allocate storage for new one and retry */
  	new_congested = kzalloc(sizeof(*new_congested), gfp);
  	if (!new_congested)
  		return NULL;

  	refcount_set(&new_congested->refcnt, 1);

  	new_congested->__bdi = bdi;

  	new_congested->blkcg_id = blkcg_id;
  	goto retry;
  
  found:

  	refcount_inc(&congested->refcnt);

  	spin_unlock_irqrestore(&cgwb_lock, flags);
  	kfree(new_congested);
  	return congested;
  }
  
  /**
   * wb_congested_put - put a wb_congested
   * @congested: wb_congested to put
   *
   * Put @congested and destroy it if the refcnt reaches zero.
   */
  void wb_congested_put(struct bdi_writeback_congested *congested)
  {

  	unsigned long flags;

  	if (!refcount_dec_and_lock_irqsave(&congested->refcnt, &cgwb_lock, &flags))

  		return;

  	/* bdi might already have been destroyed leaving @congested unlinked */

  	if (congested->__bdi) {

  		rb_erase(&congested->rb_node,

  			 &congested->__bdi->cgwb_congested_tree);
  		congested->__bdi = NULL;

  	}

  	spin_unlock_irqrestore(&cgwb_lock, flags);
  	kfree(congested);

  }
  
  static void cgwb_release_workfn(struct work_struct *work)
  {
  	struct bdi_writeback *wb = container_of(work, struct bdi_writeback,
  						release_work);

  	struct blkcg *blkcg = css_to_blkcg(wb->blkcg_css);

  	mutex_lock(&wb->bdi->cgwb_release_mutex);

  	wb_shutdown(wb);
  
  	css_put(wb->memcg_css);
  	css_put(wb->blkcg_css);

  	mutex_unlock(&wb->bdi->cgwb_release_mutex);

  	/* triggers blkg destruction if cgwb_refcnt becomes zero */
  	blkcg_cgwb_put(blkcg);

  	fprop_local_destroy_percpu(&wb->memcg_completions);

  	percpu_ref_exit(&wb->refcnt);
  	wb_exit(wb);
  	kfree_rcu(wb, rcu);

  }
  
  static void cgwb_release(struct percpu_ref *refcnt)
  {
  	struct bdi_writeback *wb = container_of(refcnt, struct bdi_writeback,
  						refcnt);

  	queue_work(cgwb_release_wq, &wb->release_work);

  }
  
  static void cgwb_kill(struct bdi_writeback *wb)
  {
  	lockdep_assert_held(&cgwb_lock);
  
  	WARN_ON(!radix_tree_delete(&wb->bdi->cgwb_tree, wb->memcg_css->id));
  	list_del(&wb->memcg_node);
  	list_del(&wb->blkcg_node);
  	percpu_ref_kill(&wb->refcnt);
  }

  static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb)
  {
  	spin_lock_irq(&cgwb_lock);
  	list_del_rcu(&wb->bdi_node);
  	spin_unlock_irq(&cgwb_lock);
  }

  static int cgwb_create(struct backing_dev_info *bdi,
  		       struct cgroup_subsys_state *memcg_css, gfp_t gfp)
  {
  	struct mem_cgroup *memcg;
  	struct cgroup_subsys_state *blkcg_css;
  	struct blkcg *blkcg;
  	struct list_head *memcg_cgwb_list, *blkcg_cgwb_list;
  	struct bdi_writeback *wb;
  	unsigned long flags;
  	int ret = 0;
  
  	memcg = mem_cgroup_from_css(memcg_css);

  	blkcg_css = cgroup_get_e_css(memcg_css->cgroup, &io_cgrp_subsys);

  	blkcg = css_to_blkcg(blkcg_css);

  	memcg_cgwb_list = &memcg->cgwb_list;

  	blkcg_cgwb_list = &blkcg->cgwb_list;
  
  	/* look up again under lock and discard on blkcg mismatch */
  	spin_lock_irqsave(&cgwb_lock, flags);
  	wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
  	if (wb && wb->blkcg_css != blkcg_css) {
  		cgwb_kill(wb);
  		wb = NULL;
  	}
  	spin_unlock_irqrestore(&cgwb_lock, flags);
  	if (wb)
  		goto out_put;
  
  	/* need to create a new one */
  	wb = kmalloc(sizeof(*wb), gfp);

  	if (!wb) {
  		ret = -ENOMEM;
  		goto out_put;
  	}

  	ret = wb_init(wb, bdi, blkcg_css->id, gfp);

  	if (ret)
  		goto err_free;
  
  	ret = percpu_ref_init(&wb->refcnt, cgwb_release, 0, gfp);
  	if (ret)
  		goto err_wb_exit;

  	ret = fprop_local_init_percpu(&wb->memcg_completions, gfp);
  	if (ret)
  		goto err_ref_exit;

  	wb->memcg_css = memcg_css;
  	wb->blkcg_css = blkcg_css;
  	INIT_WORK(&wb->release_work, cgwb_release_workfn);
  	set_bit(WB_registered, &wb->state);

  
  	/*

  	 * The root wb determines the registered state of the whole bdi and
  	 * memcg_cgwb_list and blkcg_cgwb_list's next pointers indicate
  	 * whether they're still online.  Don't link @wb if any is dead.
  	 * See wb_memcg_offline() and wb_blkcg_offline().

  	 */

  	ret = -ENODEV;
  	spin_lock_irqsave(&cgwb_lock, flags);
  	if (test_bit(WB_registered, &bdi->wb.state) &&
  	    blkcg_cgwb_list->next && memcg_cgwb_list->next) {
  		/* we might have raced another instance of this function */
  		ret = radix_tree_insert(&bdi->cgwb_tree, memcg_css->id, wb);
  		if (!ret) {

  			list_add_tail_rcu(&wb->bdi_node, &bdi->wb_list);

  			list_add(&wb->memcg_node, memcg_cgwb_list);
  			list_add(&wb->blkcg_node, blkcg_cgwb_list);

  			blkcg_cgwb_get(blkcg);

  			css_get(memcg_css);
  			css_get(blkcg_css);
  		}
  	}
  	spin_unlock_irqrestore(&cgwb_lock, flags);
  	if (ret) {
  		if (ret == -EEXIST)
  			ret = 0;

  		goto err_fprop_exit;

  	}
  	goto out_put;

  err_fprop_exit:
  	fprop_local_destroy_percpu(&wb->memcg_completions);

  err_ref_exit:
  	percpu_ref_exit(&wb->refcnt);
  err_wb_exit:
  	wb_exit(wb);
  err_free:
  	kfree(wb);
  out_put:
  	css_put(blkcg_css);
  	return ret;

  }

  /**

   * wb_get_lookup - get wb for a given memcg

   * @bdi: target bdi
   * @memcg_css: cgroup_subsys_state of the target memcg (must have positive ref)

   *

   * Try to get the wb for @memcg_css on @bdi.  The returned wb has its
   * refcount incremented.

   *
   * This function uses css_get() on @memcg_css and thus expects its refcnt
   * to be positive on invocation.  IOW, rcu_read_lock() protection on
   * @memcg_css isn't enough.  try_get it before calling this function.
   *
   * A wb is keyed by its associated memcg.  As blkcg implicitly enables
   * memcg on the default hierarchy, memcg association is guaranteed to be
   * more specific (equal or descendant to the associated blkcg) and thus can
   * identify both the memcg and blkcg associations.
   *
   * Because the blkcg associated with a memcg may change as blkcg is enabled
   * and disabled closer to root in the hierarchy, each wb keeps track of
   * both the memcg and blkcg associated with it and verifies the blkcg on
   * each lookup.  On mismatch, the existing wb is discarded and a new one is
   * created.
   */

  struct bdi_writeback *wb_get_lookup(struct backing_dev_info *bdi,
  				    struct cgroup_subsys_state *memcg_css)
  {
  	struct bdi_writeback *wb;
  
  	if (!memcg_css->parent)
  		return &bdi->wb;
  
  	rcu_read_lock();
  	wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
  	if (wb) {
  		struct cgroup_subsys_state *blkcg_css;
  
  		/* see whether the blkcg association has changed */
  		blkcg_css = cgroup_get_e_css(memcg_css->cgroup, &io_cgrp_subsys);
  		if (unlikely(wb->blkcg_css != blkcg_css || !wb_tryget(wb)))
  			wb = NULL;
  		css_put(blkcg_css);
  	}
  	rcu_read_unlock();
  
  	return wb;
  }
  
  /**
   * wb_get_create - get wb for a given memcg, create if necessary
   * @bdi: target bdi
   * @memcg_css: cgroup_subsys_state of the target memcg (must have positive ref)
   * @gfp: allocation mask to use
   *
   * Try to get the wb for @memcg_css on @bdi.  If it doesn't exist, try to
   * create one.  See wb_get_lookup() for more details.
   */

  struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
  				    struct cgroup_subsys_state *memcg_css,
  				    gfp_t gfp)

  {

  	struct bdi_writeback *wb;

  	might_sleep_if(gfpflags_allow_blocking(gfp));

  
  	if (!memcg_css->parent)
  		return &bdi->wb;
  
  	do {

  		wb = wb_get_lookup(bdi, memcg_css);

  	} while (!wb && !cgwb_create(bdi, memcg_css, gfp));
  
  	return wb;
  }

  static int cgwb_bdi_init(struct backing_dev_info *bdi)

  {

  	int ret;

  	INIT_RADIX_TREE(&bdi->cgwb_tree, GFP_ATOMIC);
  	bdi->cgwb_congested_tree = RB_ROOT;

  	mutex_init(&bdi->cgwb_release_mutex);

  	init_rwsem(&bdi->wb_switch_rwsem);

  
  	ret = wb_init(&bdi->wb, bdi, 1, GFP_KERNEL);
  	if (!ret) {

  		bdi->wb.memcg_css = &root_mem_cgroup->css;

  		bdi->wb.blkcg_css = blkcg_root_css;
  	}
  	return ret;

  }

  static void cgwb_bdi_unregister(struct backing_dev_info *bdi)

  {
  	struct radix_tree_iter iter;
  	void **slot;

  	struct bdi_writeback *wb;

  
  	WARN_ON(test_bit(WB_registered, &bdi->wb.state));
  
  	spin_lock_irq(&cgwb_lock);
  	radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
  		cgwb_kill(*slot);

  	spin_unlock_irq(&cgwb_lock);

  	mutex_lock(&bdi->cgwb_release_mutex);
  	spin_lock_irq(&cgwb_lock);

  	while (!list_empty(&bdi->wb_list)) {
  		wb = list_first_entry(&bdi->wb_list, struct bdi_writeback,
  				      bdi_node);
  		spin_unlock_irq(&cgwb_lock);
  		wb_shutdown(wb);
  		spin_lock_irq(&cgwb_lock);
  	}

  	spin_unlock_irq(&cgwb_lock);

  	mutex_unlock(&bdi->cgwb_release_mutex);

  }
  
  /**
   * wb_memcg_offline - kill all wb's associated with a memcg being offlined
   * @memcg: memcg being offlined
   *
   * Also prevents creation of any new wb's associated with @memcg.

   */

  void wb_memcg_offline(struct mem_cgroup *memcg)
  {

  	struct list_head *memcg_cgwb_list = &memcg->cgwb_list;

  	struct bdi_writeback *wb, *next;
  
  	spin_lock_irq(&cgwb_lock);
  	list_for_each_entry_safe(wb, next, memcg_cgwb_list, memcg_node)
  		cgwb_kill(wb);
  	memcg_cgwb_list->next = NULL;	/* prevent new wb's */
  	spin_unlock_irq(&cgwb_lock);
  }
  
  /**
   * wb_blkcg_offline - kill all wb's associated with a blkcg being offlined
   * @blkcg: blkcg being offlined
   *
   * Also prevents creation of any new wb's associated with @blkcg.
   */
  void wb_blkcg_offline(struct blkcg *blkcg)
  {

  	struct bdi_writeback *wb, *next;
  
  	spin_lock_irq(&cgwb_lock);
  	list_for_each_entry_safe(wb, next, &blkcg->cgwb_list, blkcg_node)
  		cgwb_kill(wb);
  	blkcg->cgwb_list.next = NULL;	/* prevent new wb's */
  	spin_unlock_irq(&cgwb_lock);
  }

  static void cgwb_bdi_exit(struct backing_dev_info *bdi)
  {
  	struct rb_node *rbn;
  
  	spin_lock_irq(&cgwb_lock);
  	while ((rbn = rb_first(&bdi->cgwb_congested_tree))) {
  		struct bdi_writeback_congested *congested =
  			rb_entry(rbn, struct bdi_writeback_congested, rb_node);
  
  		rb_erase(rbn, &bdi->cgwb_congested_tree);

  		congested->__bdi = NULL;	/* mark @congested unlinked */

  	}
  	spin_unlock_irq(&cgwb_lock);
  }

  static void cgwb_bdi_register(struct backing_dev_info *bdi)
  {
  	spin_lock_irq(&cgwb_lock);
  	list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
  	spin_unlock_irq(&cgwb_lock);
  }

  static int __init cgwb_init(void)
  {
  	/*
  	 * There can be many concurrent release work items overwhelming
  	 * system_wq.  Put them in a separate wq and limit concurrency.
  	 * There's no point in executing many of these in parallel.
  	 */
  	cgwb_release_wq = alloc_workqueue("cgwb_release", 0, 1);
  	if (!cgwb_release_wq)
  		return -ENOMEM;
  
  	return 0;
  }
  subsys_initcall(cgwb_init);

  #else	/* CONFIG_CGROUP_WRITEBACK */

  static int cgwb_bdi_init(struct backing_dev_info *bdi)
  {
  	int err;
  
  	bdi->wb_congested = kzalloc(sizeof(*bdi->wb_congested), GFP_KERNEL);
  	if (!bdi->wb_congested)
  		return -ENOMEM;

  	refcount_set(&bdi->wb_congested->refcnt, 1);

  	err = wb_init(&bdi->wb, bdi, 1, GFP_KERNEL);
  	if (err) {

  		wb_congested_put(bdi->wb_congested);

  		return err;
  	}
  	return 0;
  }

  static void cgwb_bdi_unregister(struct backing_dev_info *bdi) { }

  
  static void cgwb_bdi_exit(struct backing_dev_info *bdi)

  {
  	wb_congested_put(bdi->wb_congested);
  }

  static void cgwb_bdi_register(struct backing_dev_info *bdi)
  {
  	list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
  }
  
  static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb)
  {
  	list_del_rcu(&wb->bdi_node);
  }

  #endif	/* CONFIG_CGROUP_WRITEBACK */

  static int bdi_init(struct backing_dev_info *bdi)

  {

  	int ret;

  	bdi->dev = NULL;

  	kref_init(&bdi->refcnt);

  	bdi->min_ratio = 0;

  	bdi->max_ratio = 100;

  	bdi->max_prop_frac = FPROP_FRAC_BASE;

  	INIT_LIST_HEAD(&bdi->bdi_list);

  	INIT_LIST_HEAD(&bdi->wb_list);

  	init_waitqueue_head(&bdi->wb_waitq);

  	ret = cgwb_bdi_init(bdi);

  	return ret;

  }

  struct backing_dev_info *bdi_alloc_node(gfp_t gfp_mask, int node_id)
  {
  	struct backing_dev_info *bdi;
  
  	bdi = kmalloc_node(sizeof(struct backing_dev_info),
  			   gfp_mask | __GFP_ZERO, node_id);
  	if (!bdi)
  		return NULL;
  
  	if (bdi_init(bdi)) {
  		kfree(bdi);
  		return NULL;
  	}
  	return bdi;
  }

  EXPORT_SYMBOL(bdi_alloc_node);

  static struct rb_node **bdi_lookup_rb_node(u64 id, struct rb_node **parentp)
  {
  	struct rb_node **p = &bdi_tree.rb_node;
  	struct rb_node *parent = NULL;
  	struct backing_dev_info *bdi;
  
  	lockdep_assert_held(&bdi_lock);
  
  	while (*p) {
  		parent = *p;
  		bdi = rb_entry(parent, struct backing_dev_info, rb_node);
  
  		if (bdi->id > id)
  			p = &(*p)->rb_left;
  		else if (bdi->id < id)
  			p = &(*p)->rb_right;
  		else
  			break;
  	}
  
  	if (parentp)
  		*parentp = parent;
  	return p;
  }
  
  /**
   * bdi_get_by_id - lookup and get bdi from its id
   * @id: bdi id to lookup
   *
   * Find bdi matching @id and get it.  Returns NULL if the matching bdi
   * doesn't exist or is already unregistered.
   */
  struct backing_dev_info *bdi_get_by_id(u64 id)
  {
  	struct backing_dev_info *bdi = NULL;
  	struct rb_node **p;
  
  	spin_lock_bh(&bdi_lock);
  	p = bdi_lookup_rb_node(id, NULL);
  	if (*p) {
  		bdi = rb_entry(*p, struct backing_dev_info, rb_node);
  		bdi_get(bdi);
  	}
  	spin_unlock_bh(&bdi_lock);
  
  	return bdi;
  }

  int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args)

  {

  	struct device *dev;

  	struct rb_node *parent, **p;

  	if (bdi->dev)	/* The driver needs to use separate queues per device */
  		return 0;

  	dev = device_create_vargs(bdi_class, NULL, MKDEV(0, 0), bdi, fmt, args);

  	if (IS_ERR(dev))
  		return PTR_ERR(dev);

  	cgwb_bdi_register(bdi);

  	bdi->dev = dev;

  	bdi_debug_register(bdi, dev_name(dev));

  	set_bit(WB_registered, &bdi->wb.state);
  
  	spin_lock_bh(&bdi_lock);

  
  	bdi->id = ++bdi_id_cursor;
  
  	p = bdi_lookup_rb_node(bdi->id, &parent);
  	rb_link_node(&bdi->rb_node, parent, p);
  	rb_insert_color(&bdi->rb_node, &bdi_tree);

  	list_add_tail_rcu(&bdi->bdi_list, &bdi_list);

  	spin_unlock_bh(&bdi_lock);
  
  	trace_writeback_bdi_register(bdi);
  	return 0;

  }

  EXPORT_SYMBOL(bdi_register_va);

  int bdi_register(struct backing_dev_info *bdi, const char *fmt, ...)

  {
  	va_list args;
  	int ret;
  
  	va_start(args, fmt);

  	ret = bdi_register_va(bdi, fmt, args);

  	va_end(args);
  	return ret;
  }

  EXPORT_SYMBOL(bdi_register);

  int bdi_register_owner(struct backing_dev_info *bdi, struct device *owner)
  {
  	int rc;

  	rc = bdi_register(bdi, "%u:%u", MAJOR(owner->devt), MINOR(owner->devt));

  	if (rc)
  		return rc;

  	/* Leaking owner reference... */
  	WARN_ON(bdi->owner);

  	bdi->owner = owner;
  	get_device(owner);
  	return 0;
  }
  EXPORT_SYMBOL(bdi_register_owner);

  /*
   * Remove bdi from bdi_list, and ensure that it is no longer visible
   */
  static void bdi_remove_from_list(struct backing_dev_info *bdi)
  {
  	spin_lock_bh(&bdi_lock);

  	rb_erase(&bdi->rb_node, &bdi_tree);

  	list_del_rcu(&bdi->bdi_list);
  	spin_unlock_bh(&bdi_lock);

  	synchronize_rcu_expedited();
  }

  void bdi_unregister(struct backing_dev_info *bdi)

  {

  	/* make sure nobody finds us on the bdi_list anymore */
  	bdi_remove_from_list(bdi);
  	wb_shutdown(&bdi->wb);

  	cgwb_bdi_unregister(bdi);

  	if (bdi->dev) {
  		bdi_debug_unregister(bdi);
  		device_unregister(bdi->dev);
  		bdi->dev = NULL;
  	}

  
  	if (bdi->owner) {
  		put_device(bdi->owner);
  		bdi->owner = NULL;
  	}

  }

  static void release_bdi(struct kref *ref)
  {
  	struct backing_dev_info *bdi =
  			container_of(ref, struct backing_dev_info, refcnt);

  	if (test_bit(WB_registered, &bdi->wb.state))
  		bdi_unregister(bdi);

  	WARN_ON_ONCE(bdi->dev);
  	wb_exit(&bdi->wb);
  	cgwb_bdi_exit(bdi);

  	kfree(bdi);
  }
  
  void bdi_put(struct backing_dev_info *bdi)
  {
  	kref_put(&bdi->refcnt, release_bdi);
  }

  EXPORT_SYMBOL(bdi_put);

  static wait_queue_head_t congestion_wqh[2] = {
  		__WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
  		__WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
  	};

  static atomic_t nr_wb_congested[2];

  void clear_wb_congested(struct bdi_writeback_congested *congested, int sync)

  {

  	wait_queue_head_t *wqh = &congestion_wqh[sync];

  	enum wb_congested_state bit;

  	bit = sync ? WB_sync_congested : WB_async_congested;

  	if (test_and_clear_bit(bit, &congested->state))
  		atomic_dec(&nr_wb_congested[sync]);

  	smp_mb__after_atomic();

  	if (waitqueue_active(wqh))
  		wake_up(wqh);
  }

  EXPORT_SYMBOL(clear_wb_congested);

  void set_wb_congested(struct bdi_writeback_congested *congested, int sync)

  {

  	enum wb_congested_state bit;

  	bit = sync ? WB_sync_congested : WB_async_congested;

  	if (!test_and_set_bit(bit, &congested->state))
  		atomic_inc(&nr_wb_congested[sync]);

  }

  EXPORT_SYMBOL(set_wb_congested);

  
  /**
   * congestion_wait - wait for a backing_dev to become uncongested

   * @sync: SYNC or ASYNC IO

   * @timeout: timeout in jiffies
   *
   * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
   * write congestion.  If no backing_devs are congested then just wait for the
   * next write to be completed.
   */

  long congestion_wait(int sync, long timeout)

  {
  	long ret;

  	unsigned long start = jiffies;

  	DEFINE_WAIT(wait);

  	wait_queue_head_t *wqh = &congestion_wqh[sync];

  
  	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
  	ret = io_schedule_timeout(timeout);
  	finish_wait(wqh, &wait);

  
  	trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
  					jiffies_to_usecs(jiffies - start));

  	return ret;
  }
  EXPORT_SYMBOL(congestion_wait);

  /**

   * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a pgdat to complete writes

   * @sync: SYNC or ASYNC IO
   * @timeout: timeout in jiffies
   *

   * In the event of a congested backing_dev (any backing_dev) this waits
   * for up to @timeout jiffies for either a BDI to exit congestion of the
   * given @sync queue or a write to complete.

   *
   * The return value is 0 if the sleep is for the full timeout. Otherwise,
   * it is the number of jiffies that were still remaining when the function
   * returned. return_value == timeout implies the function did not sleep.
   */

  long wait_iff_congested(int sync, long timeout)

  {
  	long ret;
  	unsigned long start = jiffies;
  	DEFINE_WAIT(wait);
  	wait_queue_head_t *wqh = &congestion_wqh[sync];
  
  	/*

  	 * If there is no congestion, yield if necessary instead

  	 * of sleeping on the congestion queue
  	 */

  	if (atomic_read(&nr_wb_congested[sync]) == 0) {

  		cond_resched();

  		/* In case we scheduled, work out time remaining */
  		ret = timeout - (jiffies - start);
  		if (ret < 0)
  			ret = 0;
  
  		goto out;
  	}
  
  	/* Sleep until uncongested or a write happens */
  	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
  	ret = io_schedule_timeout(timeout);
  	finish_wait(wqh, &wait);
  
  out:
  	trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
  					jiffies_to_usecs(jiffies - start));
  
  	return ret;
  }
  EXPORT_SYMBOL(wait_iff_congested);