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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-only
 
 #include <linux/blkdev.h>
 #include <linux/wait.h>
 #include <linux/rbtree.h>
 #include <linux/kthread.h>
 #include <linux/backing-dev.h>
 #include <linux/blk-cgroup.h>
 #include <linux/freezer.h>
 #include <linux/fs.h>
 #include <linux/pagemap.h>
 #include <linux/mm.h>
 #include <linux/sched/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;
 EXPORT_SYMBOL_GPL(noop_backing_dev_info);
 
 static struct class *bdi_class;
 static 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;
 
 #define K(x) ((x) << (PAGE_SHIFT - 10))
 
 #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);
 
     seq_printf(m,
            "BdiWriteback:       %10lu kB\n"
            "BdiReclaimable:     %10lu kB\n"
            "BdiDirtyThresh:     %10lu kB\n"
            "DirtyThresh:        %10lu kB\n"
            "BackgroundThresh:   %10lu kB\n"
            "BdiDirtied:         %10lu kB\n"
            "BdiWritten:         %10lu kB\n"
            "BdiWriteBandwidth:  %10lu kBps\n"
            "b_dirty:            %10lu\n"
            "b_io:               %10lu\n"
            "b_more_io:          %10lu\n"
            "b_dirty_time:       %10lu\n"
            "bdi_list:           %10u\n"
            "state:              %10lx\n",
            (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);
 
     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 BDI_SHOW(name, expr)                        \
 static ssize_t name##_show(struct device *dev,              \
                struct device_attribute *attr, char *buf)    \
 {                                   \
     struct backing_dev_info *bdi = dev_get_drvdata(dev);        \
                                     \
     return sysfs_emit(buf, "%lld\n", (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 *buf)
 {
     dev_warn_once(dev,
         "the stable_pages_required attribute has been removed. Use the stable_writes queue attribute instead.\n");
     return sysfs_emit(buf, "%d\n", 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 __init default_bdi_init(void)
 {
     bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_UNBOUND |
                  WQ_SYSFS, 0);
     if (!bdi_wq)
         return -ENOMEM;
     return 0;
 }
 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_irq(&wb->work_lock);
     if (test_bit(WB_registered, &wb->state))
         queue_delayed_work(bdi_wq, &wb->dwork, timeout);
     spin_unlock_irq(&wb->work_lock);
 }
 
 static void wb_update_bandwidth_workfn(struct work_struct *work)
 {
     struct bdi_writeback *wb = container_of(to_delayed_work(work),
                         struct bdi_writeback, bw_dwork);
 
     wb_update_bandwidth(wb);
 }
 
 /*
  * 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,
            gfp_t gfp)
 {
     int i, err;
 
     memset(wb, 0, sizeof(*wb));
 
     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);
 
     atomic_set(&wb->writeback_inodes, 0);
     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);
     INIT_DELAYED_WORK(&wb->bw_dwork, wb_update_bandwidth_workfn);
     wb->dirty_sleep = jiffies;
 
     err = fprop_local_init_percpu(&wb->completions, gfp);
     if (err)
         return err;
 
     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);
     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_irq(&wb->work_lock);
     if (!test_and_clear_bit(WB_registered, &wb->state)) {
         spin_unlock_irq(&wb->work_lock);
         return;
     }
     spin_unlock_irq(&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));
     flush_delayed_work(&wb->bw_dwork);
 }
 
 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);
 }
 
 #ifdef CONFIG_CGROUP_WRITEBACK
 
 #include <linux/memcontrol.h>
 
 /*
  * cgwb_lock protects bdi->cgwb_tree, blkcg->cgwb_list, offline_cgwbs and
  * memcg->cgwb_list.  bdi->cgwb_tree is also RCU protected.
  */
 static DEFINE_SPINLOCK(cgwb_lock);
 static struct workqueue_struct *cgwb_release_wq;
 
 static LIST_HEAD(offline_cgwbs);
 static void cleanup_offline_cgwbs_workfn(struct work_struct *work);
 static DECLARE_WORK(cleanup_offline_cgwbs_work, cleanup_offline_cgwbs_workfn);
 
 static void cgwb_release_workfn(struct work_struct *work)
 {
     struct bdi_writeback *wb = container_of(work, struct bdi_writeback,
                         release_work);
     struct backing_dev_info *bdi = wb->bdi;
 
     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 no online users left */
     blkcg_unpin_online(wb->blkcg_css);
 
     fprop_local_destroy_percpu(&wb->memcg_completions);
 
     spin_lock_irq(&cgwb_lock);
     list_del(&wb->offline_node);
     spin_unlock_irq(&cgwb_lock);
 
     percpu_ref_exit(&wb->refcnt);
     wb_exit(wb);
     bdi_put(bdi);
     WARN_ON_ONCE(!list_empty(&wb->b_attached));
     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);
     list_add(&wb->offline_node, &offline_cgwbs);
     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 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);
     memcg_cgwb_list = &memcg->cgwb_list;
     blkcg_cgwb_list = blkcg_get_cgwb_list(blkcg_css);
 
     /* 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, 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_LIST_HEAD(&wb->b_attached);
     INIT_WORK(&wb->release_work, cgwb_release_workfn);
     set_bit(WB_registered, &wb->state);
     bdi_get(bdi);
 
     /*
      * 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_pin_online(blkcg_css);
             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:
     bdi_put(bdi);
     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_alloc(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);
     mutex_init(&bdi->cgwb_release_mutex);
     init_rwsem(&bdi->wb_switch_rwsem);
 
     ret = wb_init(&bdi->wb, bdi, 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);
 }
 
 /*
  * cleanup_offline_cgwbs_workfn - try to release dying cgwbs
  *
  * Try to release dying cgwbs by switching attached inodes to the nearest
  * living ancestor's writeback. Processed wbs are placed at the end
  * of the list to guarantee the forward progress.
  */
 static void cleanup_offline_cgwbs_workfn(struct work_struct *work)
 {
     struct bdi_writeback *wb;
     LIST_HEAD(processed);
 
     spin_lock_irq(&cgwb_lock);
 
     while (!list_empty(&offline_cgwbs)) {
         wb = list_first_entry(&offline_cgwbs, struct bdi_writeback,
                       offline_node);
         list_move(&wb->offline_node, &processed);
 
         /*
          * If wb is dirty, cleaning up the writeback by switching
          * attached inodes will result in an effective removal of any
          * bandwidth restrictions, which isn't the goal.  Instead,
          * it can be postponed until the next time, when all io
          * will be likely completed.  If in the meantime some inodes
          * will get re-dirtied, they should be eventually switched to
          * a new cgwb.
          */
         if (wb_has_dirty_io(wb))
             continue;
 
         if (!wb_tryget(wb))
             continue;
 
         spin_unlock_irq(&cgwb_lock);
         while (cleanup_offline_cgwb(wb))
             cond_resched();
         spin_lock_irq(&cgwb_lock);
 
         wb_put(wb);
     }
 
     if (!list_empty(&processed))
         list_splice_tail(&processed, &offline_cgwbs);
 
     spin_unlock_irq(&cgwb_lock);
 }
 
 /**
  * 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);
 
     queue_work(system_unbound_wq, &cleanup_offline_cgwbs_work);
 }
 
 /**
  * wb_blkcg_offline - kill all wb's associated with a blkcg being offlined
  * @css: blkcg being offlined
  *
  * Also prevents creation of any new wb's associated with @blkcg.
  */
 void wb_blkcg_offline(struct cgroup_subsys_state *css)
 {
     struct bdi_writeback *wb, *next;
     struct list_head *list = blkcg_get_cgwb_list(css);
 
     spin_lock_irq(&cgwb_lock);
     list_for_each_entry_safe(wb, next, list, blkcg_node)
         cgwb_kill(wb);
     list->next = NULL;  /* prevent new wb's */
     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)
 {
     return wb_init(&bdi->wb, bdi, GFP_KERNEL);
 }
 
 static void cgwb_bdi_unregister(struct backing_dev_info *bdi) { }
 
 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 */
 
 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(int node_id)
 {
     struct backing_dev_info *bdi;
 
     bdi = kzalloc_node(sizeof(*bdi), GFP_KERNEL, node_id);
     if (!bdi)
         return NULL;
 
     if (bdi_init(bdi)) {
         kfree(bdi);
         return NULL;
     }
     bdi->capabilities = BDI_CAP_WRITEBACK | BDI_CAP_WRITEBACK_ACCT;
     bdi->ra_pages = VM_READAHEAD_PAGES;
     bdi->io_pages = VM_READAHEAD_PAGES;
     timer_setup(&bdi->laptop_mode_wb_timer, laptop_mode_timer_fn, 0);
     return bdi;
 }
 EXPORT_SYMBOL(bdi_alloc);
 
 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;
 
     vsnprintf(bdi->dev_name, sizeof(bdi->dev_name), fmt, args);
     dev = device_create(bdi_class, NULL, MKDEV(0, 0), bdi, bdi->dev_name);
     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;
 }
 
 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);
 
 void bdi_set_owner(struct backing_dev_info *bdi, struct device *owner)
 {
     WARN_ON_ONCE(bdi->owner);
     bdi->owner = owner;
     get_device(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)
 {
     del_timer_sync(&bdi->laptop_mode_wb_timer);
 
     /* make sure nobody finds us on the bdi_list anymore */
     bdi_remove_from_list(bdi);
     wb_shutdown(&bdi->wb);
     cgwb_bdi_unregister(bdi);
 
     /*
      * If this BDI's min ratio has been set, use bdi_set_min_ratio() to
      * update the global bdi_min_ratio.
      */
     if (bdi->min_ratio)
         bdi_set_min_ratio(bdi, 0);
 
     if (bdi->dev) {
         bdi_debug_unregister(bdi);
         device_unregister(bdi->dev);
         bdi->dev = NULL;
     }
 
     if (bdi->owner) {
         put_device(bdi->owner);
         bdi->owner = NULL;
     }
 }
 EXPORT_SYMBOL(bdi_unregister);
 
 static void release_bdi(struct kref *ref)
 {
     struct backing_dev_info *bdi =
             container_of(ref, struct backing_dev_info, refcnt);
 
     WARN_ON_ONCE(test_bit(WB_registered, &bdi->wb.state));
     WARN_ON_ONCE(bdi->dev);
     wb_exit(&bdi->wb);
     kfree(bdi);
 }
 
 void bdi_put(struct backing_dev_info *bdi)
 {
     kref_put(&bdi->refcnt, release_bdi);
 }
 EXPORT_SYMBOL(bdi_put);
 
 struct backing_dev_info *inode_to_bdi(struct inode *inode)
 {
     struct super_block *sb;
 
     if (!inode)
         return &noop_backing_dev_info;
 
     sb = inode->i_sb;
 #ifdef CONFIG_BLOCK
     if (sb_is_blkdev_sb(sb))
         return I_BDEV(inode)->bd_disk->bdi;
 #endif
     return sb->s_bdi;
 }
 EXPORT_SYMBOL(inode_to_bdi);
 
 const char *bdi_dev_name(struct backing_dev_info *bdi)
 {
     if (!bdi || !bdi->dev)
         return bdi_unknown_name;
     return bdi->dev_name;
 }
 EXPORT_SYMBOL_GPL(bdi_dev_name);

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