UBI: Fastmap: Fix races in ubi_wl_get_peb()

[firefly-linux-kernel-4.4.55.git] / drivers / mtd / ubi / wl.c

/*
 * 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
/**
 * update_fastmap_work_fn - calls ubi_update_fastmap from a work queue
 * @wrk: the work description object
 */
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);
        spin_lock(&ubi->wl_lock);
        ubi->fm_work_scheduled = 0;
        spin_unlock(&ubi->wl_lock);
}

/**
 *  ubi_ubi_is_fm_block - returns 1 if a PEB is currently used in a fastmap.
 *  @ubi: UBI device description object
 *  @pnum: the to be checked PEB
 */
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

/**
 * wl_tree_add - add a wear-leveling entry to a WL RB-tree.
 * @e: the wear-leveling entry to add
 * @root: the root of the tree
 *
 * Note, we use (erase counter, physical eraseblock number) pairs as keys in
 * the @ubi->used and @ubi->free RB-trees.
 */
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);
}

/**
 * do_work - do one pending work.
 * @ubi: UBI device description object
 *
 * This function returns zero in case of success and a negative error code in
 * case of failure.
 */
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(ubi, "work failed with error code %d", err);
        up_read(&ubi->work_sem);

        return err;
}

/**
 * produce_free_peb - produce a free physical eraseblock.
 * @ubi: UBI device description object
 *
 * This function tries to make a free PEB by means of synchronous execution of
 * pending works. This may be needed if, for example the background thread is
 * disabled. Returns zero in case of success and a negative error code in case
 * of failure.
 */
static int produce_free_peb(struct ubi_device *ubi)
{
        int err;

        while (!ubi->free.rb_node && ubi->works_count) {
                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;
}

/**
 * in_wl_tree - check if wear-leveling entry is present in a WL RB-tree.
 * @e: the wear-leveling entry to check
 * @root: the root of the tree
 *
 * This function returns non-zero if @e is in the @root RB-tree and zero if it
 * is not.
 */
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;
}

/**
 * prot_queue_add - add physical eraseblock to the protection queue.
 * @ubi: UBI device description object
 * @e: the physical eraseblock to add
 *
 * This function adds @e to the tail of the protection queue @ubi->pq, where
 * @e will stay for %UBI_PROT_QUEUE_LEN erase operations and will be
 * temporarily protected from the wear-leveling worker. Note, @wl->lock has to
 * be locked.
 */
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);
}

/**
 * find_wl_entry - find wear-leveling entry closest to certain erase counter.
 * @ubi: UBI device description object
 * @root: the RB-tree where to look for
 * @diff: maximum possible difference from the smallest erase counter
 *
 * This function looks for a wear leveling entry with erase counter closest to
 * min + @diff, where min is the smallest erase counter.
 */
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;
}

/**
 * find_mean_wl_entry - find wear-leveling entry with medium erase counter.
 * @ubi: UBI device description object
 * @root: the RB-tree where to look for
 *
 * This function looks for a wear leveling entry with medium erase counter,
 * but not greater or equivalent than the lowest erase counter plus
 * %WL_FREE_MAX_DIFF/2.
 */
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
/**
 * find_anchor_wl_entry - find wear-leveling entry to used as anchor PEB.
 * @root: the RB-tree where to look for
 */
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;
}

/**
 * ubi_wl_get_fm_peb - find a physical erase block with a given maximal number.
 * @ubi: UBI device description object
 * @anchor: This PEB will be used as anchor PEB by fastmap
 *
 * The function returns a physical erase block with a given maximal number
 * and removes it from the wl subsystem.
 * Must be called with wl_lock held!
 */
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

/**
 * __wl_get_peb - get a physical eraseblock.
 * @ubi: UBI device description object
 *
 * This function returns a physical eraseblock in case of success and a
 * negative error code in case of failure.
 */
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(ubi, "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(ubi, "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
/**
 * return_unused_pool_pebs - returns unused PEB to the free tree.
 * @ubi: UBI device description object
 * @pool: fastmap pool description object
 */
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++;
        }
}

/**
 * refill_wl_pool - refills all the fastmap pool used by the
 * WL sub-system.
 * @ubi: UBI device description object
 */
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;
}

/**
 * refill_wl_user_pool - refills all the fastmap pool used by ubi_wl_get_peb.
 * @ubi: UBI device description object
 */
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++) {
                pool->pebs[pool->size] = __wl_get_peb(ubi);
                if (pool->pebs[pool->size] < 0)
                        break;
        }
        pool->used = 0;
}

/**
 * ubi_refill_pools - refills all fastmap PEB pools.
 * @ubi: UBI device description object
 */
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, retried = 0;
        struct ubi_fm_pool *pool = &ubi->fm_pool;
        struct ubi_fm_pool *wl_pool = &ubi->fm_wl_pool;

again:
        spin_lock(&ubi->wl_lock);
        /* We check here also for the WL pool because at this point we can
         * refill the WL pool synchronous. */
        if (pool->used == pool->size || wl_pool->used == wl_pool->size) {
                spin_unlock(&ubi->wl_lock);
                ubi_update_fastmap(ubi);
                spin_lock(&ubi->wl_lock);
        }

        if (pool->used == pool->size) {
                spin_unlock(&ubi->wl_lock);
                if (retried) {
                        ubi_err(ubi, "Unable to get a free PEB from user WL pool");
                        ret = -ENOSPC;
                        goto out;
                }
                retried = 1;
                goto again;
        }

        ubi_assert(pool->used < pool->size);
        ret = pool->pebs[pool->used++];
        prot_queue_add(ubi, ubi->lookuptbl[ret]);
        spin_unlock(&ubi->wl_lock);
out:
        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) {
                /* 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. */
                if (!ubi->fm_work_scheduled) {
                        ubi->fm_work_scheduled = 1;
                        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);
        ubi->free_count--;
        ubi_assert(ubi->free_count >= 0);
        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);

        if (peb < 0)
                return peb;

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

        return peb;
}
#endif

/**
 * prot_queue_del - remove a physical eraseblock from the protection queue.
 * @ubi: UBI device description object
 * @pnum: the physical eraseblock to remove
 *
 * This function deletes PEB @pnum from the protection queue and returns zero
 * in case of success and %-ENODEV if the PEB was not found.
 */
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;
}

/**
 * sync_erase - synchronously erase a physical eraseblock.
 * @ubi: UBI device description object
 * @e: the the physical eraseblock to erase
 * @torture: if the physical eraseblock has to be tortured
 *
 * This function returns zero in case of success and a negative error code in
 * case of failure.
 */
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(ubi, "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;
}

/**
 * serve_prot_queue - check if it is time to stop protecting PEBs.
 * @ubi: UBI device description object
 *
 * This function is called after each erase operation and removes PEBs from the
 * tail of the protection queue. These PEBs have been protected for long enough
 * and should be moved to the used tree.
 */
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);
}

/**
 * __schedule_ubi_work - schedule a work.
 * @ubi: UBI device description object
 * @wrk: the work to schedule
 *
 * This function adds a work defined by @wrk to the tail of the pending works
 * list. Can only be used if ubi->work_sem is already held in read mode!
 */
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);
}

/**
 * schedule_ubi_work - schedule a work.
 * @ubi: UBI device description object
 * @wrk: the work to schedule
 *
 * This function adds a work defined by @wrk to the tail of the pending works
 * list.
 */
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 shutdown);

#ifdef CONFIG_MTD_UBI_FASTMAP
/**
 * ubi_is_erase_work - checks whether a work is erase work.
 * @wrk: The work object to be checked
 */
int ubi_is_erase_work(struct ubi_work *wrk)
{
        return wrk->func == erase_worker;
}
#endif

/**
 * schedule_erase - schedule an erase work.
 * @ubi: UBI device description object
 * @e: the WL entry of the physical eraseblock to erase
 * @vol_id: the volume ID that last used this PEB
 * @lnum: the last used logical eraseblock number for the PEB
 * @torture: if the physical eraseblock has to be tortured
 *
 * This function returns zero in case of success and a %-ENOMEM in case of
 * failure.
 */
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;
}

/**
 * do_sync_erase - run the erase worker synchronously.
 * @ubi: UBI device description object
 * @e: the WL entry of the physical eraseblock to erase
 * @vol_id: the volume ID that last used this PEB
 * @lnum: the last used logical eraseblock number for the PEB
 * @torture: if the physical eraseblock has to be tortured
 *
 */
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
/**
 * ubi_wl_put_fm_peb - returns a PEB used in a fastmap to the wear-leveling
 * sub-system.
 * see: ubi_wl_put_peb()
 *
 * @ubi: UBI device description object
 * @fm_e: physical eraseblock to return
 * @lnum: the last used logical eraseblock number for the PEB
 * @torture: if this physical eraseblock has to be tortured
 */
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

/**
 * wear_leveling_worker - wear-leveling worker function.
 * @ubi: UBI device description object
 * @wrk: the work object
 * @shutdown: non-zero if the worker has to free memory and exit
 * because the WL-subsystem is shutting down
 *
 * This function copies a more worn out physical eraseblock to a less worn out
 * one. Returns zero in case of success and a negative error code in case of
 * failure.
 */
static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
                                int shutdown)
{
        int err, scrubbing = 0, torture = 0, protect = 0, erroneous = 0;
        int vol_id = -1, lnum = -1;
#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 (shutdown)
                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);

                        /* Give the unused PEB back */
                        wl_tree_add(e2, &ubi->free);
                        ubi->free_count++;
                        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(ubi, "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(ubi, "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(ubi, "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) {
                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)
                        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)
                goto out_ro;

        mutex_unlock(&ubi->move_mutex);
        return 0;

out_error:
        if (vol_id != -1)
                ubi_err(ubi, "error %d while moving PEB %d to PEB %d",
                        err, e1->pnum, e2->pnum);
        else
                ubi_err(ubi, "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;
}

/**
 * ensure_wear_leveling - schedule wear-leveling if it is needed.
 * @ubi: UBI device description object
 * @nested: set to non-zero if this function is called from UBI worker
 *
 * This function checks if it is time to start wear-leveling and schedules it
 * if yes. This function returns zero in case of success and a negative error
 * code in case of failure.
 */
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
/**
 * ubi_ensure_anchor_pebs - schedule wear-leveling to produce an anchor PEB.
 * @ubi: UBI device description object
 */
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

/**
 * erase_worker - physical eraseblock erase worker function.
 * @ubi: UBI device description object
 * @wl_wrk: the work object
 * @shutdown: non-zero if the worker has to free memory and exit
 * because the WL sub-system is shutting down
 *
 * This function erases a physical eraseblock and perform torture testing if
 * needed. It also takes care about marking the physical eraseblock bad if
 * needed. Returns zero in case of success and a negative error code in case of
 * failure.
 */
static int erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
                        int shutdown)
{
        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 (shutdown) {
                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(ubi, "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(ubi, "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(ubi, "no reserved/available physical eraseblocks");
                        goto out_ro;
                }
                ubi->avail_pebs -= 1;
                available_consumed = 1;
        }
        spin_unlock(&ubi->volumes_lock);

        ubi_msg(ubi, "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(ubi, "no PEBs in the reserved pool, used an available PEB");
        else if (ubi->beb_rsvd_pebs)
                ubi_msg(ubi, "%d PEBs left in the reserve",
                        ubi->beb_rsvd_pebs);
        else
                ubi_warn(ubi, "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;
}

/**
 * ubi_wl_put_peb - return a PEB to the wear-leveling sub-system.
 * @ubi: UBI device description object
 * @vol_id: the volume ID that last used this PEB
 * @lnum: the last used logical eraseblock number for the PEB
 * @pnum: physical eraseblock to return
 * @torture: if this physical eraseblock has to be tortured
 *
 * This function is called to return physical eraseblock @pnum to the pool of
 * free physical eraseblocks. The @torture flag has to be set if an I/O error
 * occurred to this @pnum and it has to be tested. This function returns zero
 * in case of success, and a negative error code in case of failure.
 */
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(ubi, "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;
}

/**
 * ubi_wl_scrub_peb - schedule a physical eraseblock for scrubbing.
 * @ubi: UBI device description object
 * @pnum: the physical eraseblock to schedule
 *
 * If a bit-flip in a physical eraseblock is detected, this physical eraseblock
 * needs scrubbing. This function schedules a physical eraseblock for
 * scrubbing which is done in background. This function returns zero in case of
 * success and a negative error code in case of failure.
 */
int ubi_wl_scrub_peb(struct ubi_device *ubi, int pnum)
{
        struct ubi_wl_entry *e;

        ubi_msg(ubi, "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(ubi, "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);
}

/**
 * ubi_wl_flush - flush all pending works.
 * @ubi: UBI device description object
 * @vol_id: the volume id to flush for
 * @lnum: the logical eraseblock number to flush for
 *
 * This function executes all pending works for a particular volume id /
 * logical eraseblock number pair. If either value is set to %UBI_ALL, then it
 * acts as a wildcard for all of the corresponding volume numbers or logical
 * eraseblock numbers. It returns zero in case of success and a negative error
 * code in case of failure.
 */
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, *tmp;
                found = 0;

                down_read(&ubi->work_sem);
                spin_lock(&ubi->wl_lock);
                list_for_each_entry_safe(wrk, tmp, &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;
}

/**
 * tree_destroy - destroy an RB-tree.
 * @root: the root of the tree to destroy
 */
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);
                }
        }
}

/**
 * ubi_thread - UBI background thread.
 * @u: the UBI device description object pointer
 */
int ubi_thread(void *u)
{
        int failures = 0;
        struct ubi_device *ubi = u;

        ubi_msg(ubi, "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(ubi, "%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(ubi, "%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;
}

/**
 * shutdown_work - shutdown all pending works.
 * @ubi: UBI device description object
 */
static void shutdown_work(struct ubi_device *ubi)
{
#ifdef CONFIG_MTD_UBI_FASTMAP
        flush_work(&ubi->fm_work);
#endif
        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);
        }
}

/**
 * ubi_wl_init - initialize the WL sub-system using attaching information.
 * @ubi: UBI device description object
 * @ai: attaching information
 *
 * This function returns zero in case of success, and a negative error code in
 * case of failure.
 */
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(ubi, "no enough physical eraseblocks (%d, need %d)",
                        ubi->avail_pebs, reserved_pebs);
                if (ubi->corr_peb_count)
                        ubi_err(ubi, "%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:
        shutdown_work(ubi);
        tree_destroy(&ubi->used);
        tree_destroy(&ubi->free);
        tree_destroy(&ubi->scrub);
        kfree(ubi->lookuptbl);
        return err;
}

/**
 * protection_queue_destroy - destroy the protection queue.
 * @ubi: UBI device description object
 */
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);
                }
        }
}

/**
 * ubi_wl_close - close the wear-leveling sub-system.
 * @ubi: UBI device description object
 */
void ubi_wl_close(struct ubi_device *ubi)
{
        dbg_wl("close the WL sub-system");
        shutdown_work(ubi);
        protection_queue_destroy(ubi);
        tree_destroy(&ubi->used);
        tree_destroy(&ubi->erroneous);
        tree_destroy(&ubi->free);
        tree_destroy(&ubi->scrub);
        kfree(ubi->lookuptbl);
}

/**
 * self_check_ec - make sure that the erase counter of a PEB is correct.
 * @ubi: UBI device description object
 * @pnum: the physical eraseblock number to check
 * @ec: the erase counter to check
 *
 * This function returns zero if the erase counter of physical eraseblock @pnum
 * is equivalent to @ec, and a negative error code if not or if an error
 * occurred.
 */
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(ubi))
                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(ubi, "self-check failed for PEB %d", pnum);
                ubi_err(ubi, "read EC is %lld, should be %d", read_ec, ec);
                dump_stack();
                err = 1;
        } else
                err = 0;

out_free:
        kfree(ec_hdr);
        return err;
}

/**
 * self_check_in_wl_tree - check that wear-leveling entry is in WL RB-tree.
 * @ubi: UBI device description object
 * @e: the wear-leveling entry to check
 * @root: the root of the tree
 *
 * This function returns zero if @e is in the @root RB-tree and %-EINVAL if it
 * is not.
 */
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(ubi))
                return 0;

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

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

/**
 * self_check_in_pq - check if wear-leveling entry is in the protection
 *                        queue.
 * @ubi: UBI device description object
 * @e: the wear-leveling entry to check
 *
 * This function returns zero if @e is in @ubi->pq and %-EINVAL if it is not.
 */
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(ubi))
                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(ubi, "self-check failed for PEB %d, EC %d, Protect queue",
                e->pnum, e->ec);
        dump_stack();
        return -EINVAL;
}