wl.c

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/*
 * @ubi: UBI device description object
 * Copyright (c) International Business Machines Corp., 2006
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
 * the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 * Authors: Artem Bityutskiy (Битюцкий Артём), Thomas Gleixner
 */

/*
 * UBI wear-leveling sub-system.
 *
 * This sub-system is responsible for wear-leveling. It works in terms of
 * physical eraseblocks and erase counters and knows nothing about logical
 * eraseblocks, volumes, etc. From this sub-system's perspective all physical
 * eraseblocks are of two types - used and free. Used physical eraseblocks are
 * those that were "get" by the 'ubi_wl_get_peb()' function, and free physical
 * eraseblocks are those that were put by the 'ubi_wl_put_peb()' function.
 *
 * Physical eraseblocks returned by 'ubi_wl_get_peb()' have only erase counter
 * header. The rest of the physical eraseblock contains only %0xFF bytes.
 *
 * When physical eraseblocks are returned to the WL sub-system by means of the
 * 'ubi_wl_put_peb()' function, they are scheduled for erasure. The erasure is
 * done asynchronously in context of the per-UBI device background thread,
 * which is also managed by the WL sub-system.
 *
 * The wear-leveling is ensured by means of moving the contents of used
 * physical eraseblocks with low erase counter to free physical eraseblocks
 * with high erase counter.
 *
 * If the WL sub-system fails to erase a physical eraseblock, it marks it as
 * bad.
 *
 * This sub-system is also responsible for scrubbing. If a bit-flip is detected
 * in a physical eraseblock, it has to be moved. Technically this is the same
 * as moving it for wear-leveling reasons.
 *
 * As it was said, for the UBI sub-system all physical eraseblocks are either
 * "free" or "used". Free eraseblock are kept in the @wl->free RB-tree, while
 * used eraseblocks are kept in @wl->used, @wl->erroneous, or @wl->scrub
 * RB-trees, as well as (temporarily) in the @wl->pq queue.
 *
 * When the WL sub-system returns a physical eraseblock, the physical
 * eraseblock is protected from being moved for some "time". For this reason,
 * the physical eraseblock is not directly moved from the @wl->free tree to the
 * @wl->used tree. There is a protection queue in between where this
 * physical eraseblock is temporarily stored (@wl->pq).
 *
 * All this protection stuff is needed because:
 *  o we don't want to move physical eraseblocks just after we have given them
 *    to the user; instead, we first want to let users fill them up with data;
 *
 *  o there is a chance that the user will put the physical eraseblock very
 *    soon, so it makes sense not to move it for some time, but wait.
 *
 * Physical eraseblocks stay protected only for limited time. But the "time" is
 * measured in erase cycles in this case. This is implemented with help of the
 * protection queue. Eraseblocks are put to the tail of this queue when they
 * are returned by the 'ubi_wl_get_peb()', and eraseblocks are removed from the
 * head of the queue on each erase operation (for any eraseblock). So the
 * length of the queue defines how may (global) erase cycles PEBs are protected.
 *
 * To put it differently, each physical eraseblock has 2 main states: free and
 * used. The former state corresponds to the @wl->free tree. The latter state
 * is split up on several sub-states:
 * o the WL movement is allowed (@wl->used tree);
 * o the WL movement is disallowed (@wl->erroneous) because the PEB is
 *   erroneous - e.g., there was a read error;
 * o the WL movement is temporarily prohibited (@wl->pq queue);
 * o scrubbing is needed (@wl->scrub tree).
 *
 * Depending on the sub-state, wear-leveling entries of the used physical
 * eraseblocks may be kept in one of those structures.
 *
 * Note, in this implementation, we keep a small in-RAM object for each physical
 * eraseblock. This is surely not a scalable solution. But it appears to be good
 * enough for moderately large flashes and it is simple. In future, one may
 * re-work this sub-system and make it more scalable.
 *
 * At the moment this sub-system does not utilize the sequence number, which
 * was introduced relatively recently. But it would be wise to do this because
 * the sequence number of a logical eraseblock characterizes how old is it. For
 * example, when we move a PEB with low erase counter, and we need to pick the
 * target PEB, we pick a PEB with the highest EC if our PEB is "old" and we
 * pick target PEB with an average EC if our PEB is not very "old". This is a
 * room for future re-works of the WL sub-system.
 */

#include <linux/slab.h>
#include <linux/crc32.h>
#include <linux/freezer.h>
#include <linux/kthread.h>
#include "ubi.h"

/* Number of physical eraseblocks reserved for wear-leveling purposes */
#define WL_RESERVED_PEBS 1

/*
 * Maximum difference between two erase counters. If this threshold is
 * exceeded, the WL sub-system starts moving data from used physical
 * eraseblocks with low erase counter to free physical eraseblocks with high
 * erase counter.
 */
#define UBI_WL_THRESHOLD CONFIG_MTD_UBI_WL_THRESHOLD

/*
 * When a physical eraseblock is moved, the WL sub-system has to pick the target
 * physical eraseblock to move to. The simplest way would be just to pick the
 * one with the highest erase counter. But in certain workloads this could lead
 * to an unlimited wear of one or few physical eraseblock. Indeed, imagine a
 * situation when the picked physical eraseblock is constantly erased after the
 * data is written to it. So, we have a constant which limits the highest erase
 * counter of the free physical eraseblock to pick. Namely, the WL sub-system
 * does not pick eraseblocks with erase counter greater than the lowest erase
 * counter plus %WL_FREE_MAX_DIFF.
 */
#define WL_FREE_MAX_DIFF (2*UBI_WL_THRESHOLD)

/*
 * Maximum number of consecutive background thread failures which is enough to
 * switch to read-only mode.
 */
#define WL_MAX_FAILURES 32

static int self_check_ec(struct ubi_device *ubi, int pnum, int ec);
static int self_check_in_wl_tree(const struct ubi_device *ubi,
                 struct ubi_wl_entry *e, struct rb_root *root);
static int self_check_in_pq(const struct ubi_device *ubi,
                struct ubi_wl_entry *e);

#ifdef CONFIG_MTD_UBI_FASTMAP

static void update_fastmap_work_fn(struct work_struct *wrk)
{
    struct ubi_device *ubi = container_of(wrk, struct ubi_device, fm_work);
    ubi_update_fastmap(ubi);
}

static int ubi_is_fm_block(struct ubi_device *ubi, int pnum)
{
    int i;

    if (!ubi->fm)
        return 0;

    for (i = 0; i < ubi->fm->used_blocks; i++)
        if (ubi->fm->e[i]->pnum == pnum)
            return 1;

    return 0;
}
#else
static int ubi_is_fm_block(struct ubi_device *ubi, int pnum)
{
    return 0;
}
#endif

static void wl_tree_add(struct ubi_wl_entry *e, struct rb_root *root)
{
    struct rb_node **p, *parent = NULL;

    p = &root->rb_node;
    while (*p) {
        struct ubi_wl_entry *e1;

        parent = *p;
        e1 = rb_entry(parent, struct ubi_wl_entry, u.rb);

        if (e->ec < e1->ec)
            p = &(*p)->rb_left;
        else if (e->ec > e1->ec)
            p = &(*p)->rb_right;
        else {
            ubi_assert(e->pnum != e1->pnum);
            if (e->pnum < e1->pnum)
                p = &(*p)->rb_left;
            else
                p = &(*p)->rb_right;
        }
    }

    rb_link_node(&e->u.rb, parent, p);
    rb_insert_color(&e->u.rb, root);
}

static int do_work(struct ubi_device *ubi)
{
    int err;
    struct ubi_work *wrk;

    cond_resched();

    /*
     * @ubi->work_sem is used to synchronize with the workers. Workers take
     * it in read mode, so many of them may be doing works at a time. But
     * the queue flush code has to be sure the whole queue of works is
     * done, and it takes the mutex in write mode.
     */
    down_read(&ubi->work_sem);
    spin_lock(&ubi->wl_lock);
    if (list_empty(&ubi->works)) {
        spin_unlock(&ubi->wl_lock);
        up_read(&ubi->work_sem);
        return 0;
    }

    wrk = list_entry(ubi->works.next, struct ubi_work, list);
    list_del(&wrk->list);
    ubi->works_count -= 1;
    ubi_assert(ubi->works_count >= 0);
    spin_unlock(&ubi->wl_lock);

    /*
     * Call the worker function. Do not touch the work structure
     * after this call as it will have been freed or reused by that
     * time by the worker function.
     */
    err = wrk->func(ubi, wrk, 0);
    if (err)
        ubi_err("work failed with error code %d", err);
    up_read(&ubi->work_sem);

    return err;
}

static int produce_free_peb(struct ubi_device *ubi)
{
    int err;

    while (!ubi->free.rb_node) {
        spin_unlock(&ubi->wl_lock);

        dbg_wl("do one work synchronously");
        err = do_work(ubi);

        spin_lock(&ubi->wl_lock);
        if (err)
            return err;
    }

    return 0;
}

static int in_wl_tree(struct ubi_wl_entry *e, struct rb_root *root)
{
    struct rb_node *p;

    p = root->rb_node;
    while (p) {
        struct ubi_wl_entry *e1;

        e1 = rb_entry(p, struct ubi_wl_entry, u.rb);

        if (e->pnum == e1->pnum) {
            ubi_assert(e == e1);
            return 1;
        }

        if (e->ec < e1->ec)
            p = p->rb_left;
        else if (e->ec > e1->ec)
            p = p->rb_right;
        else {
            ubi_assert(e->pnum != e1->pnum);
            if (e->pnum < e1->pnum)
                p = p->rb_left;
            else
                p = p->rb_right;
        }
    }

    return 0;
}

static void prot_queue_add(struct ubi_device *ubi, struct ubi_wl_entry *e)
{
    int pq_tail = ubi->pq_head - 1;

    if (pq_tail < 0)
        pq_tail = UBI_PROT_QUEUE_LEN - 1;
    ubi_assert(pq_tail >= 0 && pq_tail < UBI_PROT_QUEUE_LEN);
    list_add_tail(&e->u.list, &ubi->pq[pq_tail]);
    dbg_wl("added PEB %d EC %d to the protection queue", e->pnum, e->ec);
}

static struct ubi_wl_entry *find_wl_entry(struct ubi_device *ubi,
                      struct rb_root *root, int diff)
{
    struct rb_node *p;
    struct ubi_wl_entry *e, *prev_e = NULL;
    int max;

    e = rb_entry(rb_first(root), struct ubi_wl_entry, u.rb);
    max = e->ec + diff;

    p = root->rb_node;
    while (p) {
        struct ubi_wl_entry *e1;

        e1 = rb_entry(p, struct ubi_wl_entry, u.rb);
        if (e1->ec >= max)
            p = p->rb_left;
        else {
            p = p->rb_right;
            prev_e = e;
            e = e1;
        }
    }

    /* If no fastmap has been written and this WL entry can be used
     * as anchor PEB, hold it back and return the second best WL entry
     * such that fastmap can use the anchor PEB later. */
    if (prev_e && !ubi->fm_disabled &&
        !ubi->fm && e->pnum < UBI_FM_MAX_START)
        return prev_e;

    return e;
}

static struct ubi_wl_entry *find_mean_wl_entry(struct ubi_device *ubi,
                           struct rb_root *root)
{
    struct ubi_wl_entry *e, *first, *last;

    first = rb_entry(rb_first(root), struct ubi_wl_entry, u.rb);
    last = rb_entry(rb_last(root), struct ubi_wl_entry, u.rb);

    if (last->ec - first->ec < WL_FREE_MAX_DIFF) {
        e = rb_entry(root->rb_node, struct ubi_wl_entry, u.rb);

#ifdef CONFIG_MTD_UBI_FASTMAP
        /* If no fastmap has been written and this WL entry can be used
         * as anchor PEB, hold it back and return the second best
         * WL entry such that fastmap can use the anchor PEB later. */
        if (e && !ubi->fm_disabled && !ubi->fm &&
            e->pnum < UBI_FM_MAX_START)
            e = rb_entry(rb_next(root->rb_node),
                     struct ubi_wl_entry, u.rb);
#endif
    } else
        e = find_wl_entry(ubi, root, WL_FREE_MAX_DIFF/2);

    return e;
}

#ifdef CONFIG_MTD_UBI_FASTMAP

static struct ubi_wl_entry *find_anchor_wl_entry(struct rb_root *root)
{
    struct rb_node *p;
    struct ubi_wl_entry *e, *victim = NULL;
    int max_ec = UBI_MAX_ERASECOUNTER;

    ubi_rb_for_each_entry(p, e, root, u.rb) {
        if (e->pnum < UBI_FM_MAX_START && e->ec < max_ec) {
            victim = e;
            max_ec = e->ec;
        }
    }

    return victim;
}

static int anchor_pebs_avalible(struct rb_root *root)
{
    struct rb_node *p;
    struct ubi_wl_entry *e;

    ubi_rb_for_each_entry(p, e, root, u.rb)
        if (e->pnum < UBI_FM_MAX_START)
            return 1;

    return 0;
}

struct ubi_wl_entry *ubi_wl_get_fm_peb(struct ubi_device *ubi, int anchor)
{
    struct ubi_wl_entry *e = NULL;

    if (!ubi->free.rb_node || (ubi->free_count - ubi->beb_rsvd_pebs < 1))
        goto out;

    if (anchor)
        e = find_anchor_wl_entry(&ubi->free);
    else
        e = find_mean_wl_entry(ubi, &ubi->free);

    if (!e)
        goto out;

    self_check_in_wl_tree(ubi, e, &ubi->free);

    /* remove it from the free list,
     * the wl subsystem does no longer know this erase block */
    rb_erase(&e->u.rb, &ubi->free);
    ubi->free_count--;
out:
    return e;
}
#endif

static int __wl_get_peb(struct ubi_device *ubi)
{
    int err;
    struct ubi_wl_entry *e;

retry:
    if (!ubi->free.rb_node) {
        if (ubi->works_count == 0) {
            ubi_err("no free eraseblocks");
            ubi_assert(list_empty(&ubi->works));
            return -ENOSPC;
        }

        err = produce_free_peb(ubi);
        if (err < 0)
            return err;
        goto retry;
    }

    e = find_mean_wl_entry(ubi, &ubi->free);
    if (!e) {
        ubi_err("no free eraseblocks");
        return -ENOSPC;
    }

    self_check_in_wl_tree(ubi, e, &ubi->free);

    /*
     * Move the physical eraseblock to the protection queue where it will
     * be protected from being moved for some time.
     */
    rb_erase(&e->u.rb, &ubi->free);
    ubi->free_count--;
    dbg_wl("PEB %d EC %d", e->pnum, e->ec);
#ifndef CONFIG_MTD_UBI_FASTMAP
    /* We have to enqueue e only if fastmap is disabled,
     * is fastmap enabled prot_queue_add() will be called by
     * ubi_wl_get_peb() after removing e from the pool. */
    prot_queue_add(ubi, e);
#endif
    return e->pnum;
}

#ifdef CONFIG_MTD_UBI_FASTMAP

static void return_unused_pool_pebs(struct ubi_device *ubi,
                    struct ubi_fm_pool *pool)
{
    int i;
    struct ubi_wl_entry *e;

    for (i = pool->used; i < pool->size; i++) {
        e = ubi->lookuptbl[pool->pebs[i]];
        wl_tree_add(e, &ubi->free);
        ubi->free_count++;
    }
}

static void refill_wl_pool(struct ubi_device *ubi)
{
    struct ubi_wl_entry *e;
    struct ubi_fm_pool *pool = &ubi->fm_wl_pool;

    return_unused_pool_pebs(ubi, pool);

    for (pool->size = 0; pool->size < pool->max_size; pool->size++) {
        if (!ubi->free.rb_node ||
           (ubi->free_count - ubi->beb_rsvd_pebs < 5))
            break;

        e = find_wl_entry(ubi, &ubi->free, WL_FREE_MAX_DIFF);
        self_check_in_wl_tree(ubi, e, &ubi->free);
        rb_erase(&e->u.rb, &ubi->free);
        ubi->free_count--;

        pool->pebs[pool->size] = e->pnum;
    }
    pool->used = 0;
}

static void refill_wl_user_pool(struct ubi_device *ubi)
{
    struct ubi_fm_pool *pool = &ubi->fm_pool;

    return_unused_pool_pebs(ubi, pool);

    for (pool->size = 0; pool->size < pool->max_size; pool->size++) {
        if (!ubi->free.rb_node ||
           (ubi->free_count - ubi->beb_rsvd_pebs < 1))
            break;

        pool->pebs[pool->size] = __wl_get_peb(ubi);
        if (pool->pebs[pool->size] < 0)
            break;
    }
    pool->used = 0;
}

void ubi_refill_pools(struct ubi_device *ubi)
{
    spin_lock(&ubi->wl_lock);
    refill_wl_pool(ubi);
    refill_wl_user_pool(ubi);
    spin_unlock(&ubi->wl_lock);
}

/* ubi_wl_get_peb - works exaclty like __wl_get_peb but keeps track of
 * the fastmap pool.
 */
int ubi_wl_get_peb(struct ubi_device *ubi)
{
    int ret;
    struct ubi_fm_pool *pool = &ubi->fm_pool;
    struct ubi_fm_pool *wl_pool = &ubi->fm_wl_pool;

    if (!pool->size || !wl_pool->size || pool->used == pool->size ||
        wl_pool->used == wl_pool->size)
        ubi_update_fastmap(ubi);

    /* we got not a single free PEB */
    if (!pool->size)
        ret = -ENOSPC;
    else {
        spin_lock(&ubi->wl_lock);
        ret = pool->pebs[pool->used++];
        prot_queue_add(ubi, ubi->lookuptbl[ret]);
        spin_unlock(&ubi->wl_lock);
    }

    return ret;
}

/* get_peb_for_wl - returns a PEB to be used internally by the WL sub-system.
 *
 * @ubi: UBI device description object
 */
static struct ubi_wl_entry *get_peb_for_wl(struct ubi_device *ubi)
{
    struct ubi_fm_pool *pool = &ubi->fm_wl_pool;
    int pnum;

    if (pool->used == pool->size || !pool->size) {
        /* We cannot update the fastmap here because this
         * function is called in atomic context.
         * Let's fail here and refill/update it as soon as possible. */
        schedule_work(&ubi->fm_work);
        return NULL;
    } else {
        pnum = pool->pebs[pool->used++];
        return ubi->lookuptbl[pnum];
    }
}
#else
static struct ubi_wl_entry *get_peb_for_wl(struct ubi_device *ubi)
{
    struct ubi_wl_entry *e;

    e = find_wl_entry(ubi, &ubi->free, WL_FREE_MAX_DIFF);
    self_check_in_wl_tree(ubi, e, &ubi->free);
    rb_erase(&e->u.rb, &ubi->free);

    return e;
}

int ubi_wl_get_peb(struct ubi_device *ubi)
{
    int peb, err;

    spin_lock(&ubi->wl_lock);
    peb = __wl_get_peb(ubi);
    spin_unlock(&ubi->wl_lock);

    err = ubi_self_check_all_ff(ubi, peb, ubi->vid_hdr_aloffset,
                    ubi->peb_size - ubi->vid_hdr_aloffset);
    if (err) {
        ubi_err("new PEB %d does not contain all 0xFF bytes", peb);
        return err;
    }

    return peb;
}
#endif

static int prot_queue_del(struct ubi_device *ubi, int pnum)
{
    struct ubi_wl_entry *e;

    e = ubi->lookuptbl[pnum];
    if (!e)
        return -ENODEV;

    if (self_check_in_pq(ubi, e))
        return -ENODEV;

    list_del(&e->u.list);
    dbg_wl("deleted PEB %d from the protection queue", e->pnum);
    return 0;
}

static int sync_erase(struct ubi_device *ubi, struct ubi_wl_entry *e,
              int torture)
{
    int err;
    struct ubi_ec_hdr *ec_hdr;
    unsigned long long ec = e->ec;

    dbg_wl("erase PEB %d, old EC %llu", e->pnum, ec);

    err = self_check_ec(ubi, e->pnum, e->ec);
    if (err)
        return -EINVAL;

    ec_hdr = kzalloc(ubi->ec_hdr_alsize, GFP_NOFS);
    if (!ec_hdr)
        return -ENOMEM;

    err = ubi_io_sync_erase(ubi, e->pnum, torture);
    if (err < 0)
        goto out_free;

    ec += err;
    if (ec > UBI_MAX_ERASECOUNTER) {
        /*
         * Erase counter overflow. Upgrade UBI and use 64-bit
         * erase counters internally.
         */
        ubi_err("erase counter overflow at PEB %d, EC %llu",
            e->pnum, ec);
        err = -EINVAL;
        goto out_free;
    }

    dbg_wl("erased PEB %d, new EC %llu", e->pnum, ec);

    ec_hdr->ec = cpu_to_be64(ec);

    err = ubi_io_write_ec_hdr(ubi, e->pnum, ec_hdr);
    if (err)
        goto out_free;

    e->ec = ec;
    spin_lock(&ubi->wl_lock);
    if (e->ec > ubi->max_ec)
        ubi->max_ec = e->ec;
    spin_unlock(&ubi->wl_lock);

out_free:
    kfree(ec_hdr);
    return err;
}

static void serve_prot_queue(struct ubi_device *ubi)
{
    struct ubi_wl_entry *e, *tmp;
    int count;

    /*
     * There may be several protected physical eraseblock to remove,
     * process them all.
     */
repeat:
    count = 0;
    spin_lock(&ubi->wl_lock);
    list_for_each_entry_safe(e, tmp, &ubi->pq[ubi->pq_head], u.list) {
        dbg_wl("PEB %d EC %d protection over, move to used tree",
            e->pnum, e->ec);

        list_del(&e->u.list);
        wl_tree_add(e, &ubi->used);
        if (count++ > 32) {
            /*
             * Let's be nice and avoid holding the spinlock for
             * too long.
             */
            spin_unlock(&ubi->wl_lock);
            cond_resched();
            goto repeat;
        }
    }

    ubi->pq_head += 1;
    if (ubi->pq_head == UBI_PROT_QUEUE_LEN)
        ubi->pq_head = 0;
    ubi_assert(ubi->pq_head >= 0 && ubi->pq_head < UBI_PROT_QUEUE_LEN);
    spin_unlock(&ubi->wl_lock);
}

static void __schedule_ubi_work(struct ubi_device *ubi, struct ubi_work *wrk)
{
    spin_lock(&ubi->wl_lock);
    list_add_tail(&wrk->list, &ubi->works);
    ubi_assert(ubi->works_count >= 0);
    ubi->works_count += 1;
    if (ubi->thread_enabled && !ubi_dbg_is_bgt_disabled(ubi))
        wake_up_process(ubi->bgt_thread);
    spin_unlock(&ubi->wl_lock);
}

static void schedule_ubi_work(struct ubi_device *ubi, struct ubi_work *wrk)
{
    down_read(&ubi->work_sem);
    __schedule_ubi_work(ubi, wrk);
    up_read(&ubi->work_sem);
}

static int erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
            int cancel);

#ifdef CONFIG_MTD_UBI_FASTMAP

int ubi_is_erase_work(struct ubi_work *wrk)
{
    return wrk->func == erase_worker;
}
#endif

static int schedule_erase(struct ubi_device *ubi, struct ubi_wl_entry *e,
              int vol_id, int lnum, int torture)
{
    struct ubi_work *wl_wrk;

    ubi_assert(e);
    ubi_assert(!ubi_is_fm_block(ubi, e->pnum));

    dbg_wl("schedule erasure of PEB %d, EC %d, torture %d",
           e->pnum, e->ec, torture);

    wl_wrk = kmalloc(sizeof(struct ubi_work), GFP_NOFS);
    if (!wl_wrk)
        return -ENOMEM;

    wl_wrk->func = &erase_worker;
    wl_wrk->e = e;
    wl_wrk->vol_id = vol_id;
    wl_wrk->lnum = lnum;
    wl_wrk->torture = torture;

    schedule_ubi_work(ubi, wl_wrk);
    return 0;
}

static int do_sync_erase(struct ubi_device *ubi, struct ubi_wl_entry *e,
             int vol_id, int lnum, int torture)
{
    struct ubi_work *wl_wrk;

    dbg_wl("sync erase of PEB %i", e->pnum);

    wl_wrk = kmalloc(sizeof(struct ubi_work), GFP_NOFS);
    if (!wl_wrk)
        return -ENOMEM;

    wl_wrk->e = e;
    wl_wrk->vol_id = vol_id;
    wl_wrk->lnum = lnum;
    wl_wrk->torture = torture;

    return erase_worker(ubi, wl_wrk, 0);
}

#ifdef CONFIG_MTD_UBI_FASTMAP

int ubi_wl_put_fm_peb(struct ubi_device *ubi, struct ubi_wl_entry *fm_e,
              int lnum, int torture)
{
    struct ubi_wl_entry *e;
    int vol_id, pnum = fm_e->pnum;

    dbg_wl("PEB %d", pnum);

    ubi_assert(pnum >= 0);
    ubi_assert(pnum < ubi->peb_count);

    spin_lock(&ubi->wl_lock);
    e = ubi->lookuptbl[pnum];

    /* This can happen if we recovered from a fastmap the very
     * first time and writing now a new one. In this case the wl system
     * has never seen any PEB used by the original fastmap.
     */
    if (!e) {
        e = fm_e;
        ubi_assert(e->ec >= 0);
        ubi->lookuptbl[pnum] = e;
    } else {
        e->ec = fm_e->ec;
        kfree(fm_e);
    }

    spin_unlock(&ubi->wl_lock);

    vol_id = lnum ? UBI_FM_DATA_VOLUME_ID : UBI_FM_SB_VOLUME_ID;
    return schedule_erase(ubi, e, vol_id, lnum, torture);
}
#endif

static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
                int cancel)
{
    int err, scrubbing = 0, torture = 0, protect = 0, erroneous = 0;
    int vol_id = -1, uninitialized_var(lnum);
#ifdef CONFIG_MTD_UBI_FASTMAP
    int anchor = wrk->anchor;
#endif
    struct ubi_wl_entry *e1, *e2;
    struct ubi_vid_hdr *vid_hdr;

    kfree(wrk);
    if (cancel)
        return 0;

    vid_hdr = ubi_zalloc_vid_hdr(ubi, GFP_NOFS);
    if (!vid_hdr)
        return -ENOMEM;

    mutex_lock(&ubi->move_mutex);
    spin_lock(&ubi->wl_lock);
    ubi_assert(!ubi->move_from && !ubi->move_to);
    ubi_assert(!ubi->move_to_put);

    if (!ubi->free.rb_node ||
        (!ubi->used.rb_node && !ubi->scrub.rb_node)) {
        /*
         * No free physical eraseblocks? Well, they must be waiting in
         * the queue to be erased. Cancel movement - it will be
         * triggered again when a free physical eraseblock appears.
         *
         * No used physical eraseblocks? They must be temporarily
         * protected from being moved. They will be moved to the
         * @ubi->used tree later and the wear-leveling will be
         * triggered again.
         */
        dbg_wl("cancel WL, a list is empty: free %d, used %d",
               !ubi->free.rb_node, !ubi->used.rb_node);
        goto out_cancel;
    }

#ifdef CONFIG_MTD_UBI_FASTMAP
    /* Check whether we need to produce an anchor PEB */
    if (!anchor)
        anchor = !anchor_pebs_avalible(&ubi->free);

    if (anchor) {
        e1 = find_anchor_wl_entry(&ubi->used);
        if (!e1)
            goto out_cancel;
        e2 = get_peb_for_wl(ubi);
        if (!e2)
            goto out_cancel;

        self_check_in_wl_tree(ubi, e1, &ubi->used);
        rb_erase(&e1->u.rb, &ubi->used);
        dbg_wl("anchor-move PEB %d to PEB %d", e1->pnum, e2->pnum);
    } else if (!ubi->scrub.rb_node) {
#else
    if (!ubi->scrub.rb_node) {
#endif
        /*
         * Now pick the least worn-out used physical eraseblock and a
         * highly worn-out free physical eraseblock. If the erase
         * counters differ much enough, start wear-leveling.
         */
        e1 = rb_entry(rb_first(&ubi->used), struct ubi_wl_entry, u.rb);
        e2 = get_peb_for_wl(ubi);
        if (!e2)
            goto out_cancel;

        if (!(e2->ec - e1->ec >= UBI_WL_THRESHOLD)) {
            dbg_wl("no WL needed: min used EC %d, max free EC %d",
                   e1->ec, e2->ec);
            goto out_cancel;
        }
        self_check_in_wl_tree(ubi, e1, &ubi->used);
        rb_erase(&e1->u.rb, &ubi->used);
        dbg_wl("move PEB %d EC %d to PEB %d EC %d",
               e1->pnum, e1->ec, e2->pnum, e2->ec);
    } else {
        /* Perform scrubbing */
        scrubbing = 1;
        e1 = rb_entry(rb_first(&ubi->scrub), struct ubi_wl_entry, u.rb);
        e2 = get_peb_for_wl(ubi);
        if (!e2)
            goto out_cancel;

        self_check_in_wl_tree(ubi, e1, &ubi->scrub);
        rb_erase(&e1->u.rb, &ubi->scrub);
        dbg_wl("scrub PEB %d to PEB %d", e1->pnum, e2->pnum);
    }

    ubi->move_from = e1;
    ubi->move_to = e2;
    spin_unlock(&ubi->wl_lock);

    /*
     * Now we are going to copy physical eraseblock @e1->pnum to @e2->pnum.
     * We so far do not know which logical eraseblock our physical
     * eraseblock (@e1) belongs to. We have to read the volume identifier
     * header first.
     *
     * Note, we are protected from this PEB being unmapped and erased. The
     * 'ubi_wl_put_peb()' would wait for moving to be finished if the PEB
     * which is being moved was unmapped.
     */

    err = ubi_io_read_vid_hdr(ubi, e1->pnum, vid_hdr, 0);
    if (err && err != UBI_IO_BITFLIPS) {
        if (err == UBI_IO_FF) {
            /*
             * We are trying to move PEB without a VID header. UBI
             * always write VID headers shortly after the PEB was
             * given, so we have a situation when it has not yet
             * had a chance to write it, because it was preempted.
             * So add this PEB to the protection queue so far,
             * because presumably more data will be written there
             * (including the missing VID header), and then we'll
             * move it.
             */
            dbg_wl("PEB %d has no VID header", e1->pnum);
            protect = 1;
            goto out_not_moved;
        } else if (err == UBI_IO_FF_BITFLIPS) {
            /*
             * The same situation as %UBI_IO_FF, but bit-flips were
             * detected. It is better to schedule this PEB for
             * scrubbing.
             */
            dbg_wl("PEB %d has no VID header but has bit-flips",
                   e1->pnum);
            scrubbing = 1;
            goto out_not_moved;
        }

        ubi_err("error %d while reading VID header from PEB %d",
            err, e1->pnum);
        goto out_error;
    }

    vol_id = be32_to_cpu(vid_hdr->vol_id);
    lnum = be32_to_cpu(vid_hdr->lnum);

    err = ubi_eba_copy_leb(ubi, e1->pnum, e2->pnum, vid_hdr);
    if (err) {
        if (err == MOVE_CANCEL_RACE) {
            /*
             * The LEB has not been moved because the volume is
             * being deleted or the PEB has been put meanwhile. We
             * should prevent this PEB from being selected for
             * wear-leveling movement again, so put it to the
             * protection queue.
             */
            protect = 1;
            goto out_not_moved;
        }
        if (err == MOVE_RETRY) {
            scrubbing = 1;
            goto out_not_moved;
        }
        if (err == MOVE_TARGET_BITFLIPS || err == MOVE_TARGET_WR_ERR ||
            err == MOVE_TARGET_RD_ERR) {
            /*
             * Target PEB had bit-flips or write error - torture it.
             */
            torture = 1;
            goto out_not_moved;
        }

        if (err == MOVE_SOURCE_RD_ERR) {
            /*
             * An error happened while reading the source PEB. Do
             * not switch to R/O mode in this case, and give the
             * upper layers a possibility to recover from this,
             * e.g. by unmapping corresponding LEB. Instead, just
             * put this PEB to the @ubi->erroneous list to prevent
             * UBI from trying to move it over and over again.
             */
            if (ubi->erroneous_peb_count > ubi->max_erroneous) {
                ubi_err("too many erroneous eraseblocks (%d)",
                    ubi->erroneous_peb_count);
                goto out_error;
            }
            erroneous = 1;
            goto out_not_moved;
        }

        if (err < 0)
            goto out_error;

        ubi_assert(0);
    }

    /* The PEB has been successfully moved */
    if (scrubbing)
        ubi_msg("scrubbed PEB %d (LEB %d:%d), data moved to PEB %d",
            e1->pnum, vol_id, lnum, e2->pnum);
    ubi_free_vid_hdr(ubi, vid_hdr);

    spin_lock(&ubi->wl_lock);
    if (!ubi->move_to_put) {
        wl_tree_add(e2, &ubi->used);
        e2 = NULL;
    }
    ubi->move_from = ubi->move_to = NULL;
    ubi->move_to_put = ubi->wl_scheduled = 0;
    spin_unlock(&ubi->wl_lock);

    err = do_sync_erase(ubi, e1, vol_id, lnum, 0);
    if (err) {
        kmem_cache_free(ubi_wl_entry_slab, e1);
        if (e2)
            kmem_cache_free(ubi_wl_entry_slab, e2);
        goto out_ro;
    }

    if (e2) {
        /*
         * Well, the target PEB was put meanwhile, schedule it for
         * erasure.
         */
        dbg_wl("PEB %d (LEB %d:%d) was put meanwhile, erase",
               e2->pnum, vol_id, lnum);
        err = do_sync_erase(ubi, e2, vol_id, lnum, 0);
        if (err) {
            kmem_cache_free(ubi_wl_entry_slab, e2);
            goto out_ro;
        }
    }

    dbg_wl("done");
    mutex_unlock(&ubi->move_mutex);
    return 0;

    /*
     * For some reasons the LEB was not moved, might be an error, might be
     * something else. @e1 was not changed, so return it back. @e2 might
     * have been changed, schedule it for erasure.
     */
out_not_moved:
    if (vol_id != -1)
        dbg_wl("cancel moving PEB %d (LEB %d:%d) to PEB %d (%d)",
               e1->pnum, vol_id, lnum, e2->pnum, err);
    else
        dbg_wl("cancel moving PEB %d to PEB %d (%d)",
               e1->pnum, e2->pnum, err);
    spin_lock(&ubi->wl_lock);
    if (protect)
        prot_queue_add(ubi, e1);
    else if (erroneous) {
        wl_tree_add(e1, &ubi->erroneous);
        ubi->erroneous_peb_count += 1;
    } else if (scrubbing)
        wl_tree_add(e1, &ubi->scrub);
    else
        wl_tree_add(e1, &ubi->used);
    ubi_assert(!ubi->move_to_put);
    ubi->move_from = ubi->move_to = NULL;
    ubi->wl_scheduled = 0;
    spin_unlock(&ubi->wl_lock);

    ubi_free_vid_hdr(ubi, vid_hdr);
    err = do_sync_erase(ubi, e2, vol_id, lnum, torture);
    if (err) {
        kmem_cache_free(ubi_wl_entry_slab, e2);
        goto out_ro;
    }
    mutex_unlock(&ubi->move_mutex);
    return 0;

out_error:
    if (vol_id != -1)
        ubi_err("error %d while moving PEB %d to PEB %d",
            err, e1->pnum, e2->pnum);
    else
        ubi_err("error %d while moving PEB %d (LEB %d:%d) to PEB %d",
            err, e1->pnum, vol_id, lnum, e2->pnum);
    spin_lock(&ubi->wl_lock);
    ubi->move_from = ubi->move_to = NULL;
    ubi->move_to_put = ubi->wl_scheduled = 0;
    spin_unlock(&ubi->wl_lock);

    ubi_free_vid_hdr(ubi, vid_hdr);
    kmem_cache_free(ubi_wl_entry_slab, e1);
    kmem_cache_free(ubi_wl_entry_slab, e2);

out_ro:
    ubi_ro_mode(ubi);
    mutex_unlock(&ubi->move_mutex);
    ubi_assert(err != 0);
    return err < 0 ? err : -EIO;

out_cancel:
    ubi->wl_scheduled = 0;
    spin_unlock(&ubi->wl_lock);
    mutex_unlock(&ubi->move_mutex);
    ubi_free_vid_hdr(ubi, vid_hdr);
    return 0;
}

static int ensure_wear_leveling(struct ubi_device *ubi, int nested)
{
    int err = 0;
    struct ubi_wl_entry *e1;
    struct ubi_wl_entry *e2;
    struct ubi_work *wrk;

    spin_lock(&ubi->wl_lock);
    if (ubi->wl_scheduled)
        /* Wear-leveling is already in the work queue */
        goto out_unlock;

    /*
     * If the ubi->scrub tree is not empty, scrubbing is needed, and the
     * the WL worker has to be scheduled anyway.
     */
    if (!ubi->scrub.rb_node) {
        if (!ubi->used.rb_node || !ubi->free.rb_node)
            /* No physical eraseblocks - no deal */
            goto out_unlock;

        /*
         * We schedule wear-leveling only if the difference between the
         * lowest erase counter of used physical eraseblocks and a high
         * erase counter of free physical eraseblocks is greater than
         * %UBI_WL_THRESHOLD.
         */
        e1 = rb_entry(rb_first(&ubi->used), struct ubi_wl_entry, u.rb);
        e2 = find_wl_entry(ubi, &ubi->free, WL_FREE_MAX_DIFF);

        if (!(e2->ec - e1->ec >= UBI_WL_THRESHOLD))
            goto out_unlock;
        dbg_wl("schedule wear-leveling");
    } else
        dbg_wl("schedule scrubbing");

    ubi->wl_scheduled = 1;
    spin_unlock(&ubi->wl_lock);

    wrk = kmalloc(sizeof(struct ubi_work), GFP_NOFS);
    if (!wrk) {
        err = -ENOMEM;
        goto out_cancel;
    }

    wrk->anchor = 0;
    wrk->func = &wear_leveling_worker;
    if (nested)
        __schedule_ubi_work(ubi, wrk);
    else
        schedule_ubi_work(ubi, wrk);
    return err;

out_cancel:
    spin_lock(&ubi->wl_lock);
    ubi->wl_scheduled = 0;
out_unlock:
    spin_unlock(&ubi->wl_lock);
    return err;
}

#ifdef CONFIG_MTD_UBI_FASTMAP

int ubi_ensure_anchor_pebs(struct ubi_device *ubi)
{
    struct ubi_work *wrk;

    spin_lock(&ubi->wl_lock);
    if (ubi->wl_scheduled) {
        spin_unlock(&ubi->wl_lock);
        return 0;
    }
    ubi->wl_scheduled = 1;
    spin_unlock(&ubi->wl_lock);

    wrk = kmalloc(sizeof(struct ubi_work), GFP_NOFS);
    if (!wrk) {
        spin_lock(&ubi->wl_lock);
        ubi->wl_scheduled = 0;
        spin_unlock(&ubi->wl_lock);
        return -ENOMEM;
    }

    wrk->anchor = 1;
    wrk->func = &wear_leveling_worker;
    schedule_ubi_work(ubi, wrk);
    return 0;
}
#endif

static int erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
            int cancel)
{
    struct ubi_wl_entry *e = wl_wrk->e;
    int pnum = e->pnum;
    int vol_id = wl_wrk->vol_id;
    int lnum = wl_wrk->lnum;
    int err, available_consumed = 0;

    if (cancel) {
        dbg_wl("cancel erasure of PEB %d EC %d", pnum, e->ec);
        kfree(wl_wrk);
        kmem_cache_free(ubi_wl_entry_slab, e);
        return 0;
    }

    dbg_wl("erase PEB %d EC %d LEB %d:%d",
           pnum, e->ec, wl_wrk->vol_id, wl_wrk->lnum);

    ubi_assert(!ubi_is_fm_block(ubi, e->pnum));

    err = sync_erase(ubi, e, wl_wrk->torture);
    if (!err) {
        /* Fine, we've erased it successfully */
        kfree(wl_wrk);

        spin_lock(&ubi->wl_lock);
        wl_tree_add(e, &ubi->free);
        ubi->free_count++;
        spin_unlock(&ubi->wl_lock);

        /*
         * One more erase operation has happened, take care about
         * protected physical eraseblocks.
         */
        serve_prot_queue(ubi);

        /* And take care about wear-leveling */
        err = ensure_wear_leveling(ubi, 1);
        return err;
    }

    ubi_err("failed to erase PEB %d, error %d", pnum, err);
    kfree(wl_wrk);

    if (err == -EINTR || err == -ENOMEM || err == -EAGAIN ||
        err == -EBUSY) {
        int err1;

        /* Re-schedule the LEB for erasure */
        err1 = schedule_erase(ubi, e, vol_id, lnum, 0);
        if (err1) {
            err = err1;
            goto out_ro;
        }
        return err;
    }

    kmem_cache_free(ubi_wl_entry_slab, e);
    if (err != -EIO)
        /*
         * If this is not %-EIO, we have no idea what to do. Scheduling
         * this physical eraseblock for erasure again would cause
         * errors again and again. Well, lets switch to R/O mode.
         */
        goto out_ro;

    /* It is %-EIO, the PEB went bad */

    if (!ubi->bad_allowed) {
        ubi_err("bad physical eraseblock %d detected", pnum);
        goto out_ro;
    }

    spin_lock(&ubi->volumes_lock);
    if (ubi->beb_rsvd_pebs == 0) {
        if (ubi->avail_pebs == 0) {
            spin_unlock(&ubi->volumes_lock);
            ubi_err("no reserved/available physical eraseblocks");
            goto out_ro;
        }
        ubi->avail_pebs -= 1;
        available_consumed = 1;
    }
    spin_unlock(&ubi->volumes_lock);

    ubi_msg("mark PEB %d as bad", pnum);
    err = ubi_io_mark_bad(ubi, pnum);
    if (err)
        goto out_ro;

    spin_lock(&ubi->volumes_lock);
    if (ubi->beb_rsvd_pebs > 0) {
        if (available_consumed) {
            /*
             * The amount of reserved PEBs increased since we last
             * checked.
             */
            ubi->avail_pebs += 1;
            available_consumed = 0;
        }
        ubi->beb_rsvd_pebs -= 1;
    }
    ubi->bad_peb_count += 1;
    ubi->good_peb_count -= 1;
    ubi_calculate_reserved(ubi);
    if (available_consumed)
        ubi_warn("no PEBs in the reserved pool, used an available PEB");
    else if (ubi->beb_rsvd_pebs)
        ubi_msg("%d PEBs left in the reserve", ubi->beb_rsvd_pebs);
    else
        ubi_warn("last PEB from the reserve was used");
    spin_unlock(&ubi->volumes_lock);

    return err;

out_ro:
    if (available_consumed) {
        spin_lock(&ubi->volumes_lock);
        ubi->avail_pebs += 1;
        spin_unlock(&ubi->volumes_lock);
    }
    ubi_ro_mode(ubi);
    return err;
}

int ubi_wl_put_peb(struct ubi_device *ubi, int vol_id, int lnum,
           int pnum, int torture)
{
    int err;
    struct ubi_wl_entry *e;

    dbg_wl("PEB %d", pnum);
    ubi_assert(pnum >= 0);
    ubi_assert(pnum < ubi->peb_count);

retry:
    spin_lock(&ubi->wl_lock);
    e = ubi->lookuptbl[pnum];
    if (e == ubi->move_from) {
        /*
         * User is putting the physical eraseblock which was selected to
         * be moved. It will be scheduled for erasure in the
         * wear-leveling worker.
         */
        dbg_wl("PEB %d is being moved, wait", pnum);
        spin_unlock(&ubi->wl_lock);

        /* Wait for the WL worker by taking the @ubi->move_mutex */
        mutex_lock(&ubi->move_mutex);
        mutex_unlock(&ubi->move_mutex);
        goto retry;
    } else if (e == ubi->move_to) {
        /*
         * User is putting the physical eraseblock which was selected
         * as the target the data is moved to. It may happen if the EBA
         * sub-system already re-mapped the LEB in 'ubi_eba_copy_leb()'
         * but the WL sub-system has not put the PEB to the "used" tree
         * yet, but it is about to do this. So we just set a flag which
         * will tell the WL worker that the PEB is not needed anymore
         * and should be scheduled for erasure.
         */
        dbg_wl("PEB %d is the target of data moving", pnum);
        ubi_assert(!ubi->move_to_put);
        ubi->move_to_put = 1;
        spin_unlock(&ubi->wl_lock);
        return 0;
    } else {
        if (in_wl_tree(e, &ubi->used)) {
            self_check_in_wl_tree(ubi, e, &ubi->used);
            rb_erase(&e->u.rb, &ubi->used);
        } else if (in_wl_tree(e, &ubi->scrub)) {
            self_check_in_wl_tree(ubi, e, &ubi->scrub);
            rb_erase(&e->u.rb, &ubi->scrub);
        } else if (in_wl_tree(e, &ubi->erroneous)) {
            self_check_in_wl_tree(ubi, e, &ubi->erroneous);
            rb_erase(&e->u.rb, &ubi->erroneous);
            ubi->erroneous_peb_count -= 1;
            ubi_assert(ubi->erroneous_peb_count >= 0);
            /* Erroneous PEBs should be tortured */
            torture = 1;
        } else {
            err = prot_queue_del(ubi, e->pnum);
            if (err) {
                ubi_err("PEB %d not found", pnum);
                ubi_ro_mode(ubi);
                spin_unlock(&ubi->wl_lock);
                return err;
            }
        }
    }
    spin_unlock(&ubi->wl_lock);

    err = schedule_erase(ubi, e, vol_id, lnum, torture);
    if (err) {
        spin_lock(&ubi->wl_lock);
        wl_tree_add(e, &ubi->used);
        spin_unlock(&ubi->wl_lock);
    }

    return err;
}

int ubi_wl_scrub_peb(struct ubi_device *ubi, int pnum)
{
    struct ubi_wl_entry *e;

    ubi_msg("schedule PEB %d for scrubbing", pnum);

retry:
    spin_lock(&ubi->wl_lock);
    e = ubi->lookuptbl[pnum];
    if (e == ubi->move_from || in_wl_tree(e, &ubi->scrub) ||
                   in_wl_tree(e, &ubi->erroneous)) {
        spin_unlock(&ubi->wl_lock);
        return 0;
    }

    if (e == ubi->move_to) {
        /*
         * This physical eraseblock was used to move data to. The data
         * was moved but the PEB was not yet inserted to the proper
         * tree. We should just wait a little and let the WL worker
         * proceed.
         */
        spin_unlock(&ubi->wl_lock);
        dbg_wl("the PEB %d is not in proper tree, retry", pnum);
        yield();
        goto retry;
    }

    if (in_wl_tree(e, &ubi->used)) {
        self_check_in_wl_tree(ubi, e, &ubi->used);
        rb_erase(&e->u.rb, &ubi->used);
    } else {
        int err;

        err = prot_queue_del(ubi, e->pnum);
        if (err) {
            ubi_err("PEB %d not found", pnum);
            ubi_ro_mode(ubi);
            spin_unlock(&ubi->wl_lock);
            return err;
        }
    }

    wl_tree_add(e, &ubi->scrub);
    spin_unlock(&ubi->wl_lock);

    /*
     * Technically scrubbing is the same as wear-leveling, so it is done
     * by the WL worker.
     */
    return ensure_wear_leveling(ubi, 0);
}

int ubi_wl_flush(struct ubi_device *ubi, int vol_id, int lnum)
{
    int err = 0;
    int found = 1;

    /*
     * Erase while the pending works queue is not empty, but not more than
     * the number of currently pending works.
     */
    dbg_wl("flush pending work for LEB %d:%d (%d pending works)",
           vol_id, lnum, ubi->works_count);

    while (found) {
        struct ubi_work *wrk;
        found = 0;

        down_read(&ubi->work_sem);
        spin_lock(&ubi->wl_lock);
        list_for_each_entry(wrk, &ubi->works, list) {
            if ((vol_id == UBI_ALL || wrk->vol_id == vol_id) &&
                (lnum == UBI_ALL || wrk->lnum == lnum)) {
                list_del(&wrk->list);
                ubi->works_count -= 1;
                ubi_assert(ubi->works_count >= 0);
                spin_unlock(&ubi->wl_lock);

                err = wrk->func(ubi, wrk, 0);
                if (err) {
                    up_read(&ubi->work_sem);
                    return err;
                }

                spin_lock(&ubi->wl_lock);
                found = 1;
                break;
            }
        }
        spin_unlock(&ubi->wl_lock);
        up_read(&ubi->work_sem);
    }

    /*
     * Make sure all the works which have been done in parallel are
     * finished.
     */
    down_write(&ubi->work_sem);
    up_write(&ubi->work_sem);

    return err;
}

static void tree_destroy(struct rb_root *root)
{
    struct rb_node *rb;
    struct ubi_wl_entry *e;

    rb = root->rb_node;
    while (rb) {
        if (rb->rb_left)
            rb = rb->rb_left;
        else if (rb->rb_right)
            rb = rb->rb_right;
        else {
            e = rb_entry(rb, struct ubi_wl_entry, u.rb);

            rb = rb_parent(rb);
            if (rb) {
                if (rb->rb_left == &e->u.rb)
                    rb->rb_left = NULL;
                else
                    rb->rb_right = NULL;
            }

            kmem_cache_free(ubi_wl_entry_slab, e);
        }
    }
}

int ubi_thread(void *u)
{
    int failures = 0;
    struct ubi_device *ubi = u;

    ubi_msg("background thread \"%s\" started, PID %d",
        ubi->bgt_name, task_pid_nr(current));

    set_freezable();
    for (;;) {
        int err;

        if (kthread_should_stop())
            break;

        if (try_to_freeze())
            continue;

        spin_lock(&ubi->wl_lock);
        if (list_empty(&ubi->works) || ubi->ro_mode ||
            !ubi->thread_enabled || ubi_dbg_is_bgt_disabled(ubi)) {
            set_current_state(TASK_INTERRUPTIBLE);
            spin_unlock(&ubi->wl_lock);
            schedule();
            continue;
        }
        spin_unlock(&ubi->wl_lock);

        err = do_work(ubi);
        if (err) {
            ubi_err("%s: work failed with error code %d",
                ubi->bgt_name, err);
            if (failures++ > WL_MAX_FAILURES) {
                /*
                 * Too many failures, disable the thread and
                 * switch to read-only mode.
                 */
                ubi_msg("%s: %d consecutive failures",
                    ubi->bgt_name, WL_MAX_FAILURES);
                ubi_ro_mode(ubi);
                ubi->thread_enabled = 0;
                continue;
            }
        } else
            failures = 0;

        cond_resched();
    }

    dbg_wl("background thread \"%s\" is killed", ubi->bgt_name);
    return 0;
}

static void cancel_pending(struct ubi_device *ubi)
{
    while (!list_empty(&ubi->works)) {
        struct ubi_work *wrk;

        wrk = list_entry(ubi->works.next, struct ubi_work, list);
        list_del(&wrk->list);
        wrk->func(ubi, wrk, 1);
        ubi->works_count -= 1;
        ubi_assert(ubi->works_count >= 0);
    }
}

int ubi_wl_init(struct ubi_device *ubi, struct ubi_attach_info *ai)
{
    int err, i, reserved_pebs, found_pebs = 0;
    struct rb_node *rb1, *rb2;
    struct ubi_ainf_volume *av;
    struct ubi_ainf_peb *aeb, *tmp;
    struct ubi_wl_entry *e;

    ubi->used = ubi->erroneous = ubi->free = ubi->scrub = RB_ROOT;
    spin_lock_init(&ubi->wl_lock);
    mutex_init(&ubi->move_mutex);
    init_rwsem(&ubi->work_sem);
    ubi->max_ec = ai->max_ec;
    INIT_LIST_HEAD(&ubi->works);
#ifdef CONFIG_MTD_UBI_FASTMAP
    INIT_WORK(&ubi->fm_work, update_fastmap_work_fn);
#endif

    sprintf(ubi->bgt_name, UBI_BGT_NAME_PATTERN, ubi->ubi_num);

    err = -ENOMEM;
    ubi->lookuptbl = kzalloc(ubi->peb_count * sizeof(void *), GFP_KERNEL);
    if (!ubi->lookuptbl)
        return err;

    for (i = 0; i < UBI_PROT_QUEUE_LEN; i++)
        INIT_LIST_HEAD(&ubi->pq[i]);
    ubi->pq_head = 0;

    list_for_each_entry_safe(aeb, tmp, &ai->erase, u.list) {
        cond_resched();

        e = kmem_cache_alloc(ubi_wl_entry_slab, GFP_KERNEL);
        if (!e)
            goto out_free;

        e->pnum = aeb->pnum;
        e->ec = aeb->ec;
        ubi_assert(!ubi_is_fm_block(ubi, e->pnum));
        ubi->lookuptbl[e->pnum] = e;
        if (schedule_erase(ubi, e, aeb->vol_id, aeb->lnum, 0)) {
            kmem_cache_free(ubi_wl_entry_slab, e);
            goto out_free;
        }

        found_pebs++;
    }

    ubi->free_count = 0;
    list_for_each_entry(aeb, &ai->free, u.list) {
        cond_resched();

        e = kmem_cache_alloc(ubi_wl_entry_slab, GFP_KERNEL);
        if (!e)
            goto out_free;

        e->pnum = aeb->pnum;
        e->ec = aeb->ec;
        ubi_assert(e->ec >= 0);
        ubi_assert(!ubi_is_fm_block(ubi, e->pnum));

        wl_tree_add(e, &ubi->free);
        ubi->free_count++;

        ubi->lookuptbl[e->pnum] = e;

        found_pebs++;
    }

    ubi_rb_for_each_entry(rb1, av, &ai->volumes, rb) {
        ubi_rb_for_each_entry(rb2, aeb, &av->root, u.rb) {
            cond_resched();

            e = kmem_cache_alloc(ubi_wl_entry_slab, GFP_KERNEL);
            if (!e)
                goto out_free;

            e->pnum = aeb->pnum;
            e->ec = aeb->ec;
            ubi->lookuptbl[e->pnum] = e;

            if (!aeb->scrub) {
                dbg_wl("add PEB %d EC %d to the used tree",
                       e->pnum, e->ec);
                wl_tree_add(e, &ubi->used);
            } else {
                dbg_wl("add PEB %d EC %d to the scrub tree",
                       e->pnum, e->ec);
                wl_tree_add(e, &ubi->scrub);
            }

            found_pebs++;
        }
    }

    dbg_wl("found %i PEBs", found_pebs);

    if (ubi->fm)
        ubi_assert(ubi->good_peb_count == \
               found_pebs + ubi->fm->used_blocks);
    else
        ubi_assert(ubi->good_peb_count == found_pebs);

    reserved_pebs = WL_RESERVED_PEBS;
#ifdef CONFIG_MTD_UBI_FASTMAP
    /* Reserve enough LEBs to store two fastmaps. */
    reserved_pebs += (ubi->fm_size / ubi->leb_size) * 2;
#endif

    if (ubi->avail_pebs < reserved_pebs) {
        ubi_err("no enough physical eraseblocks (%d, need %d)",
            ubi->avail_pebs, reserved_pebs);
        if (ubi->corr_peb_count)
            ubi_err("%d PEBs are corrupted and not used",
                ubi->corr_peb_count);
        goto out_free;
    }
    ubi->avail_pebs -= reserved_pebs;
    ubi->rsvd_pebs += reserved_pebs;

    /* Schedule wear-leveling if needed */
    err = ensure_wear_leveling(ubi, 0);
    if (err)
        goto out_free;

    return 0;

out_free:
    cancel_pending(ubi);
    tree_destroy(&ubi->used);
    tree_destroy(&ubi->free);
    tree_destroy(&ubi->scrub);
    kfree(ubi->lookuptbl);
    return err;
}

static void protection_queue_destroy(struct ubi_device *ubi)
{
    int i;
    struct ubi_wl_entry *e, *tmp;

    for (i = 0; i < UBI_PROT_QUEUE_LEN; ++i) {
        list_for_each_entry_safe(e, tmp, &ubi->pq[i], u.list) {
            list_del(&e->u.list);
            kmem_cache_free(ubi_wl_entry_slab, e);
        }
    }
}

void ubi_wl_close(struct ubi_device *ubi)
{
    dbg_wl("close the WL sub-system");
    cancel_pending(ubi);
    protection_queue_destroy(ubi);
    tree_destroy(&ubi->used);
    tree_destroy(&ubi->erroneous);
    tree_destroy(&ubi->free);
    tree_destroy(&ubi->scrub);
    kfree(ubi->lookuptbl);
}

static int self_check_ec(struct ubi_device *ubi, int pnum, int ec)
{
    int err;
    long long read_ec;
    struct ubi_ec_hdr *ec_hdr;

    if (!ubi->dbg->chk_gen)
        return 0;

    ec_hdr = kzalloc(ubi->ec_hdr_alsize, GFP_NOFS);
    if (!ec_hdr)
        return -ENOMEM;

    err = ubi_io_read_ec_hdr(ubi, pnum, ec_hdr, 0);
    if (err && err != UBI_IO_BITFLIPS) {
        /* The header does not have to exist */
        err = 0;
        goto out_free;
    }

    read_ec = be64_to_cpu(ec_hdr->ec);
    if (ec != read_ec && read_ec - ec > 1) {
        ubi_err("self-check failed for PEB %d", pnum);
        ubi_err("read EC is %lld, should be %d", read_ec, ec);
        dump_stack();
        err = 1;
    } else
        err = 0;

out_free:
    kfree(ec_hdr);
    return err;
}

static int self_check_in_wl_tree(const struct ubi_device *ubi,
                 struct ubi_wl_entry *e, struct rb_root *root)
{
    if (!ubi->dbg->chk_gen)
        return 0;

    if (in_wl_tree(e, root))
        return 0;

    ubi_err("self-check failed for PEB %d, EC %d, RB-tree %p ",
        e->pnum, e->ec, root);
    dump_stack();
    return -EINVAL;
}

static int self_check_in_pq(const struct ubi_device *ubi,
                struct ubi_wl_entry *e)
{
    struct ubi_wl_entry *p;
    int i;

    if (!ubi->dbg->chk_gen)
        return 0;

    for (i = 0; i < UBI_PROT_QUEUE_LEN; ++i)
        list_for_each_entry(p, &ubi->pq[i], u.list)
            if (p == e)
                return 0;

    ubi_err("self-check failed for PEB %d, EC %d, Protect queue",
        e->pnum, e->ec);
    dump_stack();
    return -EINVAL;
}