text: /*
   * 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.
   */
  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.
   */
  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 *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 */
  