Merge tag 'trace-v5.15-3' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt...

[mirror_ubuntu-jammy-kernel.git] / mm / backing-dev.c

// 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/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 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);
}

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));

        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);

        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)
                goto out_put_bdi;

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

#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 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 no online users left */
        blkcg_unpin_online(blkcg);

        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);
        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 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, 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);

        /*
         * 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_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_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
 * @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_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 */

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(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 (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);
        kfree(bdi);
}

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

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);

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_bdi_congested(struct backing_dev_info *bdi, 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, &bdi->wb.congested))
                atomic_dec(&nr_wb_congested[sync]);
        smp_mb__after_atomic();
        if (waitqueue_active(wqh))
                wake_up(wqh);
}
EXPORT_SYMBOL(clear_bdi_congested);

void set_bdi_congested(struct backing_dev_info *bdi, int sync)
{
        enum wb_congested_state bit;

        bit = sync ? WB_sync_congested : WB_async_congested;
        if (!test_and_set_bit(bit, &bdi->wb.congested))
                atomic_inc(&nr_wb_congested[sync]);
}
EXPORT_SYMBOL(set_bdi_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);