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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 unit.
 *
 * This unit 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 unit'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 unit 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 unit.
 *
 * 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.
 *
 * The 'ubi_wl_get_peb()' function accepts data type hints which help to pick
 * an "optimal" physical eraseblock. For example, when it is known that the
 * physical eraseblock will be "put" soon because it contains short-term data,
 * the WL unit may pick a free physical eraseblock with low erase counter, and
 * so forth.
 *
 * If the WL unit fails to erase a physical eraseblock, it marks it as bad.
 *
 * This unit 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 unit all physical eraseblocks are either "free"
 * or "used". Free eraseblock are kept in the @wl->free RB-tree, while used
 * eraseblocks are kept in a set of different RB-trees: @wl->used,
 * @wl->prot.pnum, @wl->prot.aec, and @wl->scrub.
 *
 * 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 unit and make it more scalable.
 *
 * At the moment this unit 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 unit.
 *
 * FIXME: looks too complex, should be simplified (later).
 */

#ifdef UBI_LINUX
#include <linux/slab.h>
#include <linux/crc32.h>
#include <linux/freezer.h>
#include <linux/kthread.h>
#endif

#include <ubi_uboot.h>
#include "ubi.h"

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

/*
 * How many erase cycles are short term, unknown, and long term physical
 * eraseblocks protected.
 */
#define ST_PROTECTION 16
#define U_PROTECTION  10
#define LT_PROTECTION 4

/*
 * Maximum difference between two erase counters. If this threshold is
 * exceeded, the WL unit 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 unit 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 unit does
 * not pick eraseblocks with erase counter greater then 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

/**
 * struct ubi_wl_prot_entry - PEB protection entry.
 * @rb_pnum: link in the @wl->prot.pnum RB-tree
 * @rb_aec: link in the @wl->prot.aec RB-tree
 * @abs_ec: the absolute erase counter value when the protection ends
 * @e: the wear-leveling entry of the physical eraseblock under protection
 *
 * When the WL unit 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 one more tree in between where this physical eraseblock is
 * temporarily stored (@wl->prot).
 *
 * 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; this is
 *    especially important in case of "short term" physical eraseblocks.
 *
 * 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
 * absolute erase counter (@wl->abs_ec). When it reaches certain value, the
 * physical eraseblocks are moved from the protection trees (@wl->prot.*) to
 * the @wl->used tree.
 *
 * Protected physical eraseblocks are searched by physical eraseblock number
 * (when they are put) and by the absolute erase counter (to check if it is
 * time to move them to the @wl->used tree). So there are actually 2 RB-trees
 * storing the protected physical eraseblocks: @wl->prot.pnum and
 * @wl->prot.aec. They are referred to as the "protection" trees. The
 * first one is indexed by the physical eraseblock number. The second one is
 * indexed by the absolute erase counter. Both trees store
 * &struct ubi_wl_prot_entry objects.
 *
 * 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 temporarily prohibited (@wl->prot.pnum and
 * @wl->prot.aec trees);
 * 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 trees.
 */
00170 struct ubi_wl_prot_entry {
      struct rb_node rb_pnum;
      struct rb_node rb_aec;
      unsigned long long abs_ec;
      struct ubi_wl_entry *e;
};

/**
 * struct ubi_work - UBI work description data structure.
 * @list: a link in the list of pending works
 * @func: worker function
 * @priv: private data of the worker function
 *
 * @e: physical eraseblock to erase
 * @torture: if the physical eraseblock has to be tortured
 *
 * The @func pointer points to the worker function. If the @cancel argument is
 * not zero, the worker has to free the resources and exit immediately. The
 * worker has to return zero in case of success and a negative error code in
 * case of failure.
 */
00191 struct ubi_work {
      struct list_head list;
      int (*func)(struct ubi_device *ubi, struct ubi_work *wrk, int cancel);
      /* The below fields are only relevant to erasure works */
      struct ubi_wl_entry *e;
      int torture;
};

#ifdef CONFIG_MTD_UBI_DEBUG_PARANOID
static int paranoid_check_ec(struct ubi_device *ubi, int pnum, int ec);
static int paranoid_check_in_wl_tree(struct ubi_wl_entry *e,
                             struct rb_root *root);
#else
#define paranoid_check_ec(ubi, pnum, ec) 0
#define paranoid_check_in_wl_tree(e, root)
#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, 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->rb, parent, p);
      rb_insert_color(&e->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("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;

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

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

            spin_lock(&ubi->wl_lock);
      }
      spin_unlock(&ubi->wl_lock);

      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, 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_tree_add - add physical eraseblock to protection trees.
 * @ubi: UBI device description object
 * @e: the physical eraseblock to add
 * @pe: protection entry object to use
 * @abs_ec: absolute erase counter value when this physical eraseblock has
 * to be removed from the protection trees.
 *
 * @wl->lock has to be locked.
 */
static void prot_tree_add(struct ubi_device *ubi, struct ubi_wl_entry *e,
                    struct ubi_wl_prot_entry *pe, int abs_ec)
{
      struct rb_node **p, *parent = NULL;
      struct ubi_wl_prot_entry *pe1;

      pe->e = e;
      pe->abs_ec = ubi->abs_ec + abs_ec;

      p = &ubi->prot.pnum.rb_node;
      while (*p) {
            parent = *p;
            pe1 = rb_entry(parent, struct ubi_wl_prot_entry, rb_pnum);

            if (e->pnum < pe1->e->pnum)
                  p = &(*p)->rb_left;
            else
                  p = &(*p)->rb_right;
      }
      rb_link_node(&pe->rb_pnum, parent, p);
      rb_insert_color(&pe->rb_pnum, &ubi->prot.pnum);

      p = &ubi->prot.aec.rb_node;
      parent = NULL;
      while (*p) {
            parent = *p;
            pe1 = rb_entry(parent, struct ubi_wl_prot_entry, rb_aec);

            if (pe->abs_ec < pe1->abs_ec)
                  p = &(*p)->rb_left;
            else
                  p = &(*p)->rb_right;
      }
      rb_link_node(&pe->rb_aec, parent, p);
      rb_insert_color(&pe->rb_aec, &ubi->prot.aec);
}

/**
 * find_wl_entry - find wear-leveling entry closest to certain erase counter.
 * @root: the RB-tree where to look for
 * @max: highest possible erase counter
 *
 * This function looks for a wear leveling entry with erase counter closest to
 * @max and less then @max.
 */
static struct ubi_wl_entry *find_wl_entry(struct rb_root *root, int max)
{
      struct rb_node *p;
      struct ubi_wl_entry *e;

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

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

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

      return e;
}

/**
 * ubi_wl_get_peb - get a physical eraseblock.
 * @ubi: UBI device description object
 * @dtype: type of data which will be stored in this physical eraseblock
 *
 * This function returns a physical eraseblock in case of success and a
 * negative error code in case of failure. Might sleep.
 */
int ubi_wl_get_peb(struct ubi_device *ubi, int dtype)
{
      int err, protect, medium_ec;
      struct ubi_wl_entry *e, *first, *last;
      struct ubi_wl_prot_entry *pe;

      ubi_assert(dtype == UBI_LONGTERM || dtype == UBI_SHORTTERM ||
               dtype == UBI_UNKNOWN);

      pe = kmalloc(sizeof(struct ubi_wl_prot_entry), GFP_NOFS);
      if (!pe)
            return -ENOMEM;

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

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

      switch (dtype) {
            case UBI_LONGTERM:
                  /*
                   * For long term data we pick a physical eraseblock
                   * with high erase counter. But the highest erase
                   * counter we can pick is bounded by the the lowest
                   * erase counter plus %WL_FREE_MAX_DIFF.
                   */
                  e = find_wl_entry(&ubi->free, WL_FREE_MAX_DIFF);
                  protect = LT_PROTECTION;
                  break;
            case UBI_UNKNOWN:
                  /*
                   * For unknown data we pick a physical eraseblock with
                   * medium erase counter. But we by no means can pick a
                   * physical eraseblock with erase counter greater or
                   * equivalent than the lowest erase counter plus
                   * %WL_FREE_MAX_DIFF.
                   */
                  first = rb_entry(rb_first(&ubi->free),
                               struct ubi_wl_entry, rb);
                  last = rb_entry(rb_last(&ubi->free),
                              struct ubi_wl_entry, rb);

                  if (last->ec - first->ec < WL_FREE_MAX_DIFF)
                        e = rb_entry(ubi->free.rb_node,
                                    struct ubi_wl_entry, rb);
                  else {
                        medium_ec = (first->ec + WL_FREE_MAX_DIFF)/2;
                        e = find_wl_entry(&ubi->free, medium_ec);
                  }
                  protect = U_PROTECTION;
                  break;
            case UBI_SHORTTERM:
                  /*
                   * For short term data we pick a physical eraseblock
                   * with the lowest erase counter as we expect it will
                   * be erased soon.
                   */
                  e = rb_entry(rb_first(&ubi->free),
                             struct ubi_wl_entry, rb);
                  protect = ST_PROTECTION;
                  break;
            default:
                  protect = 0;
                  e = NULL;
                  BUG();
      }

      /*
       * Move the physical eraseblock to the protection trees where it will
       * be protected from being moved for some time.
       */
      paranoid_check_in_wl_tree(e, &ubi->free);
      rb_erase(&e->rb, &ubi->free);
      prot_tree_add(ubi, e, pe, protect);

      dbg_wl("PEB %d EC %d, protection %d", e->pnum, e->ec, protect);
      spin_unlock(&ubi->wl_lock);

      return e->pnum;
}

/**
 * prot_tree_del - remove a physical eraseblock from the protection trees
 * @ubi: UBI device description object
 * @pnum: the physical eraseblock to remove
 *
 * This function returns PEB @pnum from the protection trees and returns zero
 * in case of success and %-ENODEV if the PEB was not found in the protection
 * trees.
 */
static int prot_tree_del(struct ubi_device *ubi, int pnum)
{
      struct rb_node *p;
      struct ubi_wl_prot_entry *pe = NULL;

      p = ubi->prot.pnum.rb_node;
      while (p) {

            pe = rb_entry(p, struct ubi_wl_prot_entry, rb_pnum);

            if (pnum == pe->e->pnum)
                  goto found;

            if (pnum < pe->e->pnum)
                  p = p->rb_left;
            else
                  p = p->rb_right;
      }

      return -ENODEV;

found:
      ubi_assert(pe->e->pnum == pnum);
      rb_erase(&pe->rb_aec, &ubi->prot.aec);
      rb_erase(&pe->rb_pnum, &ubi->prot.pnum);
      kfree(pe);
      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 = paranoid_check_ec(ubi, e->pnum, e->ec);
      if (err > 0)
            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;
}

/**
 * check_protection_over - check if it is time to stop protecting some
 * physical eraseblocks.
 * @ubi: UBI device description object
 *
 * This function is called after each erase operation, when the absolute erase
 * counter is incremented, to check if some physical eraseblock  have not to be
 * protected any longer. These physical eraseblocks are moved from the
 * protection trees to the used tree.
 */
static void check_protection_over(struct ubi_device *ubi)
{
      struct ubi_wl_prot_entry *pe;

      /*
       * There may be several protected physical eraseblock to remove,
       * process them all.
       */
      while (1) {
            spin_lock(&ubi->wl_lock);
            if (!ubi->prot.aec.rb_node) {
                  spin_unlock(&ubi->wl_lock);
                  break;
            }

            pe = rb_entry(rb_first(&ubi->prot.aec),
                        struct ubi_wl_prot_entry, rb_aec);

            if (pe->abs_ec > ubi->abs_ec) {
                  spin_unlock(&ubi->wl_lock);
                  break;
            }

            dbg_wl("PEB %d protection over, abs_ec %llu, PEB abs_ec %llu",
                   pe->e->pnum, ubi->abs_ec, pe->abs_ec);
            rb_erase(&pe->rb_aec, &ubi->prot.aec);
            rb_erase(&pe->rb_pnum, &ubi->prot.pnum);
            wl_tree_add(pe->e, &ubi->used);
            spin_unlock(&ubi->wl_lock);

            kfree(pe);
            cond_resched();
      }
}

/**
 * schedule_ubi_work - schedule a work.
 * @ubi: UBI device description object
 * @wrk: the work to schedule
 *
 * This function enqueues 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)
{
      spin_lock(&ubi->wl_lock);
      list_add_tail(&wrk->list, &ubi->works);
      ubi_assert(ubi->works_count >= 0);
      ubi->works_count += 1;

      /*
       * U-Boot special: We have no bgt_thread in U-Boot!
       * So just call do_work() here directly.
       */
      do_work(ubi);

      spin_unlock(&ubi->wl_lock);
}

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

/**
 * schedule_erase - schedule an erase work.
 * @ubi: UBI device description object
 * @e: the WL entry of the physical eraseblock to erase
 * @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 torture)
{
      struct ubi_work *wl_wrk;

      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->torture = torture;

      schedule_ubi_work(ubi, wl_wrk);
      return 0;
}

/**
 * wear_leveling_worker - wear-leveling worker function.
 * @ubi: UBI device description object
 * @wrk: the work object
 * @cancel: non-zero if the worker has to free memory and exit
 *
 * 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 cancel)
{
      int err, put = 0, scrubbing = 0, protect = 0;
      struct ubi_wl_prot_entry *uninitialized_var(pe);
      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;
      }

      if (!ubi->scrub.rb_node) {
            /*
             * 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, rb);
            e2 = find_wl_entry(&ubi->free, WL_FREE_MAX_DIFF);

            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;
            }
            paranoid_check_in_wl_tree(e1, &ubi->used);
            rb_erase(&e1->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, rb);
            e2 = find_wl_entry(&ubi->free, WL_FREE_MAX_DIFF);
            paranoid_check_in_wl_tree(e1, &ubi->scrub);
            rb_erase(&e1->rb, &ubi->scrub);
            dbg_wl("scrub PEB %d to PEB %d", e1->pnum, e2->pnum);
      }

      paranoid_check_in_wl_tree(e2, &ubi->free);
      rb_erase(&e2->rb, &ubi->free);
      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_PEB_FREE) {
                  /*
                   * 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 did not have
                   * chance to write it down because it was preempted.
                   * Just re-schedule the work, so that next time it will
                   * likely have the VID header in place.
                   */
                  dbg_wl("PEB %d has no VID header", e1->pnum);
                  goto out_not_moved;
            }

            ubi_err("error %d while reading VID header from PEB %d",
                  err, e1->pnum);
            if (err > 0)
                  err = -EIO;
            goto out_error;
      }

      err = ubi_eba_copy_leb(ubi, e1->pnum, e2->pnum, vid_hdr);
      if (err) {

            if (err < 0)
                  goto out_error;
            if (err == 1)
                  goto out_not_moved;

            /*
             * For some reason the LEB was not moved - it might be because
             * the volume is being deleted. We should prevent this PEB from
             * being selected for wear-levelling movement for some "time",
             * so put it to the protection tree.
             */

            dbg_wl("cancelled moving PEB %d", e1->pnum);
            pe = kmalloc(sizeof(struct ubi_wl_prot_entry), GFP_NOFS);
            if (!pe) {
                  err = -ENOMEM;
                  goto out_error;
            }

            protect = 1;
      }

      ubi_free_vid_hdr(ubi, vid_hdr);
      spin_lock(&ubi->wl_lock);
      if (protect)
            prot_tree_add(ubi, e1, pe, protect);
      if (!ubi->move_to_put)
            wl_tree_add(e2, &ubi->used);
      else
            put = 1;
      ubi->move_from = ubi->move_to = NULL;
      ubi->move_to_put = ubi->wl_scheduled = 0;
      spin_unlock(&ubi->wl_lock);

      if (put) {
            /*
             * Well, the target PEB was put meanwhile, schedule it for
             * erasure.
             */
            dbg_wl("PEB %d was put meanwhile, erase", e2->pnum);
            err = schedule_erase(ubi, e2, 0);
            if (err)
                  goto out_error;
      }

      if (!protect) {
            err = schedule_erase(ubi, e1, 0);
            if (err)
                  goto out_error;
      }


      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
       * be changed, schedule it for erasure.
       */
out_not_moved:
      ubi_free_vid_hdr(ubi, vid_hdr);
      spin_lock(&ubi->wl_lock);
      if (scrubbing)
            wl_tree_add(e1, &ubi->scrub);
      else
            wl_tree_add(e1, &ubi->used);
      ubi->move_from = ubi->move_to = NULL;
      ubi->move_to_put = ubi->wl_scheduled = 0;
      spin_unlock(&ubi->wl_lock);

      err = schedule_erase(ubi, e2, 0);
      if (err)
            goto out_error;

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

out_error:
      ubi_err("error %d while moving PEB %d to PEB %d",
            err, e1->pnum, e2->pnum);

      ubi_free_vid_hdr(ubi, vid_hdr);
      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);

      kmem_cache_free(ubi_wl_entry_slab, e1);
      kmem_cache_free(ubi_wl_entry_slab, e2);
      ubi_ro_mode(ubi);

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

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
 *
 * 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 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 then
             * %UBI_WL_THRESHOLD.
             */
            e1 = rb_entry(rb_first(&ubi->used), struct ubi_wl_entry, rb);
            e2 = find_wl_entry(&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->func = &wear_leveling_worker;
      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;
}

/**
 * erase_worker - physical eraseblock erase worker function.
 * @ubi: UBI device description object
 * @wl_wrk: the work object
 * @cancel: non-zero if the worker has to free memory and exit
 *
 * 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 cancel)
{
      struct ubi_wl_entry *e = wl_wrk->e;
      int pnum = e->pnum, err, need;

      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", pnum, e->ec);

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

            spin_lock(&ubi->wl_lock);
            ubi->abs_ec += 1;
            wl_tree_add(e, &ubi->free);
            spin_unlock(&ubi->wl_lock);

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

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

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

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

            /* Re-schedule the LEB for erasure */
            err1 = schedule_erase(ubi, e, 0);
            if (err1) {
                  err = err1;
                  goto out_ro;
            }
            return err;
      } else 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 RO 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);
      need = ubi->beb_rsvd_level - ubi->beb_rsvd_pebs + 1;
      if (need > 0) {
            need = ubi->avail_pebs >= need ? need : ubi->avail_pebs;
            ubi->avail_pebs -= need;
            ubi->rsvd_pebs += need;
            ubi->beb_rsvd_pebs += need;
            if (need > 0)
                  ubi_msg("reserve more %d PEBs", need);
      }

      if (ubi->beb_rsvd_pebs == 0) {
            spin_unlock(&ubi->volumes_lock);
            ubi_err("no reserved physical eraseblocks");
            goto out_ro;
      }

      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);
      ubi->beb_rsvd_pebs -= 1;
      ubi->bad_peb_count += 1;
      ubi->good_peb_count -= 1;
      ubi_calculate_reserved(ubi);
      if (ubi->beb_rsvd_pebs == 0)
            ubi_warn("last PEB from the reserved pool was used");
      spin_unlock(&ubi->volumes_lock);

      return err;

out_ro:
      ubi_ro_mode(ubi);
      return err;
}

/**
 * ubi_wl_put_peb - return a physical eraseblock to the wear-leveling unit.
 * @ubi: UBI device description object
 * @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 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
             * unit already re-mapped the LEB in 'ubi_eba_copy_leb()' but
             * the WL unit 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)) {
                  paranoid_check_in_wl_tree(e, &ubi->used);
                  rb_erase(&e->rb, &ubi->used);
            } else if (in_wl_tree(e, &ubi->scrub)) {
                  paranoid_check_in_wl_tree(e, &ubi->scrub);
                  rb_erase(&e->rb, &ubi->scrub);
            } else {
                  err = prot_tree_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, 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("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)) {
            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)) {
            paranoid_check_in_wl_tree(e, &ubi->used);
            rb_erase(&e->rb, &ubi->used);
      } else {
            int err;

            err = prot_tree_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);
}

/**
 * ubi_wl_flush - flush all pending works.
 * @ubi: UBI device description object
 *
 * This function returns zero in case of success and a negative error code in
 * case of failure.
 */
int ubi_wl_flush(struct ubi_device *ubi)
{
      int err;

      /*
       * Erase while the pending works queue is not empty, but not more then
       * the number of currently pending works.
       */
      dbg_wl("flush (%d pending works)", ubi->works_count);
      while (ubi->works_count) {
            err = do_work(ubi);
            if (err)
                  return err;
      }

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

      /*
       * And in case last was the WL worker and it cancelled the LEB
       * movement, flush again.
       */
      while (ubi->works_count) {
            dbg_wl("flush more (%d pending works)", ubi->works_count);
            err = do_work(ubi);
            if (err)
                  return err;
      }

      return 0;
}

/**
 * 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, rb);

                  rb = rb_parent(rb);
                  if (rb) {
                        if (rb->rb_left == &e->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("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) {
                  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);
                        break;
                  }
            } else
                  failures = 0;

            cond_resched();
      }

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

/**
 * cancel_pending - cancel all pending works.
 * @ubi: UBI device description object
 */
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);
      }
}

/**
 * ubi_wl_init_scan - initialize the wear-leveling unit using scanning
 * information.
 * @ubi: UBI device description object
 * @si: scanning information
 *
 * This function returns zero in case of success, and a negative error code in
 * case of failure.
 */
int ubi_wl_init_scan(struct ubi_device *ubi, struct ubi_scan_info *si)
{
      int err;
      struct rb_node *rb1, *rb2;
      struct ubi_scan_volume *sv;
      struct ubi_scan_leb *seb, *tmp;
      struct ubi_wl_entry *e;


      ubi->used = ubi->free = ubi->scrub = RB_ROOT;
      ubi->prot.pnum = ubi->prot.aec = RB_ROOT;
      spin_lock_init(&ubi->wl_lock);
      mutex_init(&ubi->move_mutex);
      init_rwsem(&ubi->work_sem);
      ubi->max_ec = si->max_ec;
      INIT_LIST_HEAD(&ubi->works);

      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;

      list_for_each_entry_safe(seb, tmp, &si->erase, u.list) {
            cond_resched();

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

            e->pnum = seb->pnum;
            e->ec = seb->ec;
            ubi->lookuptbl[e->pnum] = e;
            if (schedule_erase(ubi, e, 0)) {
                  kmem_cache_free(ubi_wl_entry_slab, e);
                  goto out_free;
            }
      }

      list_for_each_entry(seb, &si->free, u.list) {
            cond_resched();

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

            e->pnum = seb->pnum;
            e->ec = seb->ec;
            ubi_assert(e->ec >= 0);
            wl_tree_add(e, &ubi->free);
            ubi->lookuptbl[e->pnum] = e;
      }

      list_for_each_entry(seb, &si->corr, u.list) {
            cond_resched();

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

            e->pnum = seb->pnum;
            e->ec = seb->ec;
            ubi->lookuptbl[e->pnum] = e;
            if (schedule_erase(ubi, e, 0)) {
                  kmem_cache_free(ubi_wl_entry_slab, e);
                  goto out_free;
            }
      }

      ubi_rb_for_each_entry(rb1, sv, &si->volumes, rb) {
            ubi_rb_for_each_entry(rb2, seb, &sv->root, u.rb) {
                  cond_resched();

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

                  e->pnum = seb->pnum;
                  e->ec = seb->ec;
                  ubi->lookuptbl[e->pnum] = e;
                  if (!seb->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);
                  }
            }
      }

      if (ubi->avail_pebs < WL_RESERVED_PEBS) {
            ubi_err("no enough physical eraseblocks (%d, need %d)",
                  ubi->avail_pebs, WL_RESERVED_PEBS);
            goto out_free;
      }
      ubi->avail_pebs -= WL_RESERVED_PEBS;
      ubi->rsvd_pebs += WL_RESERVED_PEBS;

      /* Schedule wear-leveling if needed */
      err = ensure_wear_leveling(ubi);
      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;
}

/**
 * protection_trees_destroy - destroy the protection RB-trees.
 * @ubi: UBI device description object
 */
static void protection_trees_destroy(struct ubi_device *ubi)
{
      struct rb_node *rb;
      struct ubi_wl_prot_entry *pe;

      rb = ubi->prot.aec.rb_node;
      while (rb) {
            if (rb->rb_left)
                  rb = rb->rb_left;
            else if (rb->rb_right)
                  rb = rb->rb_right;
            else {
                  pe = rb_entry(rb, struct ubi_wl_prot_entry, rb_aec);

                  rb = rb_parent(rb);
                  if (rb) {
                        if (rb->rb_left == &pe->rb_aec)
                              rb->rb_left = NULL;
                        else
                              rb->rb_right = NULL;
                  }

                  kmem_cache_free(ubi_wl_entry_slab, pe->e);
                  kfree(pe);
            }
      }
}

/**
 * ubi_wl_close - close the wear-leveling unit.
 * @ubi: UBI device description object
 */
void ubi_wl_close(struct ubi_device *ubi)
{
      dbg_wl("close the UBI wear-leveling unit");

      cancel_pending(ubi);
      protection_trees_destroy(ubi);
      tree_destroy(&ubi->used);
      tree_destroy(&ubi->free);
      tree_destroy(&ubi->scrub);
      kfree(ubi->lookuptbl);
}

#ifdef CONFIG_MTD_UBI_DEBUG_PARANOID

/**
 * paranoid_check_ec - make sure that the erase counter of a physical eraseblock
 * 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, %1 if not, and a negative error code if an error
 * occurred.
 */
static int paranoid_check_ec(struct ubi_device *ubi, int pnum, int ec)
{
      int err;
      long long read_ec;
      struct ubi_ec_hdr *ec_hdr;

      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) {
            ubi_err("paranoid check failed for PEB %d", pnum);
            ubi_err("read EC is %lld, should be %d", read_ec, ec);
            ubi_dbg_dump_stack();
            err = 1;
      } else
            err = 0;

out_free:
      kfree(ec_hdr);
      return err;
}

/**
 * paranoid_check_in_wl_tree - make sure that a 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 zero if @e is in the @root RB-tree and %1 if it
 * is not.
 */
static int paranoid_check_in_wl_tree(struct ubi_wl_entry *e,
                             struct rb_root *root)
{
      if (in_wl_tree(e, root))
            return 0;

      ubi_err("paranoid check failed for PEB %d, EC %d, RB-tree %p ",
            e->pnum, e->ec, root);
      ubi_dbg_dump_stack();
      return 1;
}

#endif /* CONFIG_MTD_UBI_DEBUG_PARANOID */

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