scrub.c

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/*
 * Copyright (C) 2011 STRATO.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * 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 021110-1307, USA.
 */

#include <linux/blkdev.h>
#include <linux/ratelimit.h>
#include "ctree.h"
#include "volumes.h"
#include "disk-io.h"
#include "ordered-data.h"
#include "transaction.h"
#include "backref.h"
#include "extent_io.h"
#include "check-integrity.h"
#include "rcu-string.h"

/*
 * This is only the first step towards a full-features scrub. It reads all
 * extent and super block and verifies the checksums. In case a bad checksum
 * is found or the extent cannot be read, good data will be written back if
 * any can be found.
 *
 * Future enhancements:
 *  - In case an unrepairable extent is encountered, track which files are
 *    affected and report them
 *  - track and record media errors, throw out bad devices
 *  - add a mode to also read unallocated space
 */

struct scrub_block;
struct scrub_dev;

#define SCRUB_PAGES_PER_BIO 16  /* 64k per bio */
#define SCRUB_BIOS_PER_DEV  16  /* 1 MB per device in flight */
#define SCRUB_MAX_PAGES_PER_BLOCK   16  /* 64k per node/leaf/sector */

struct scrub_page {
    struct scrub_block  *sblock;
    struct page     *page;
    struct btrfs_device *dev;
    u64         flags;  /* extent flags */
    u64         generation;
    u64         logical;
    u64         physical;
    struct {
        unsigned int    mirror_num:8;
        unsigned int    have_csum:1;
        unsigned int    io_error:1;
    };
    u8          csum[BTRFS_CSUM_SIZE];
};

struct scrub_bio {
    int         index;
    struct scrub_dev    *sdev;
    struct bio      *bio;
    int         err;
    u64         logical;
    u64         physical;
    struct scrub_page   *pagev[SCRUB_PAGES_PER_BIO];
    int         page_count;
    int         next_free;
    struct btrfs_work   work;
};

struct scrub_block {
    struct scrub_page   pagev[SCRUB_MAX_PAGES_PER_BLOCK];
    int         page_count;
    atomic_t        outstanding_pages;
    atomic_t        ref_count; /* free mem on transition to zero */
    struct scrub_dev    *sdev;
    struct {
        unsigned int    header_error:1;
        unsigned int    checksum_error:1;
        unsigned int    no_io_error_seen:1;
        unsigned int    generation_error:1; /* also sets header_error */
    };
};

struct scrub_dev {
    struct scrub_bio    *bios[SCRUB_BIOS_PER_DEV];
    struct btrfs_device *dev;
    int         first_free;
    int         curr;
    atomic_t        in_flight;
    atomic_t        fixup_cnt;
    spinlock_t      list_lock;
    wait_queue_head_t   list_wait;
    u16         csum_size;
    struct list_head    csum_list;
    atomic_t        cancel_req;
    int         readonly;
    int         pages_per_bio; /* <= SCRUB_PAGES_PER_BIO */
    u32         sectorsize;
    u32         nodesize;
    u32         leafsize;
    /*
     * statistics
     */
    struct btrfs_scrub_progress stat;
    spinlock_t      stat_lock;
};

struct scrub_fixup_nodatasum {
    struct scrub_dev    *sdev;
    u64         logical;
    struct btrfs_root   *root;
    struct btrfs_work   work;
    int         mirror_num;
};

struct scrub_warning {
    struct btrfs_path   *path;
    u64         extent_item_size;
    char            *scratch_buf;
    char            *msg_buf;
    const char      *errstr;
    sector_t        sector;
    u64         logical;
    struct btrfs_device *dev;
    int         msg_bufsize;
    int         scratch_bufsize;
};


static int scrub_handle_errored_block(struct scrub_block *sblock_to_check);
static int scrub_setup_recheck_block(struct scrub_dev *sdev,
                     struct btrfs_mapping_tree *map_tree,
                     u64 length, u64 logical,
                     struct scrub_block *sblock);
static int scrub_recheck_block(struct btrfs_fs_info *fs_info,
                   struct scrub_block *sblock, int is_metadata,
                   int have_csum, u8 *csum, u64 generation,
                   u16 csum_size);
static void scrub_recheck_block_checksum(struct btrfs_fs_info *fs_info,
                     struct scrub_block *sblock,
                     int is_metadata, int have_csum,
                     const u8 *csum, u64 generation,
                     u16 csum_size);
static void scrub_complete_bio_end_io(struct bio *bio, int err);
static int scrub_repair_block_from_good_copy(struct scrub_block *sblock_bad,
                         struct scrub_block *sblock_good,
                         int force_write);
static int scrub_repair_page_from_good_copy(struct scrub_block *sblock_bad,
                        struct scrub_block *sblock_good,
                        int page_num, int force_write);
static int scrub_checksum_data(struct scrub_block *sblock);
static int scrub_checksum_tree_block(struct scrub_block *sblock);
static int scrub_checksum_super(struct scrub_block *sblock);
static void scrub_block_get(struct scrub_block *sblock);
static void scrub_block_put(struct scrub_block *sblock);
static int scrub_add_page_to_bio(struct scrub_dev *sdev,
                 struct scrub_page *spage);
static int scrub_pages(struct scrub_dev *sdev, u64 logical, u64 len,
               u64 physical, u64 flags, u64 gen, int mirror_num,
               u8 *csum, int force);
static void scrub_bio_end_io(struct bio *bio, int err);
static void scrub_bio_end_io_worker(struct btrfs_work *work);
static void scrub_block_complete(struct scrub_block *sblock);


static void scrub_free_csums(struct scrub_dev *sdev)
{
    while (!list_empty(&sdev->csum_list)) {
        struct btrfs_ordered_sum *sum;
        sum = list_first_entry(&sdev->csum_list,
                       struct btrfs_ordered_sum, list);
        list_del(&sum->list);
        kfree(sum);
    }
}

static noinline_for_stack void scrub_free_dev(struct scrub_dev *sdev)
{
    int i;

    if (!sdev)
        return;

    /* this can happen when scrub is cancelled */
    if (sdev->curr != -1) {
        struct scrub_bio *sbio = sdev->bios[sdev->curr];

        for (i = 0; i < sbio->page_count; i++) {
            BUG_ON(!sbio->pagev[i]);
            BUG_ON(!sbio->pagev[i]->page);
            scrub_block_put(sbio->pagev[i]->sblock);
        }
        bio_put(sbio->bio);
    }

    for (i = 0; i < SCRUB_BIOS_PER_DEV; ++i) {
        struct scrub_bio *sbio = sdev->bios[i];

        if (!sbio)
            break;
        kfree(sbio);
    }

    scrub_free_csums(sdev);
    kfree(sdev);
}

static noinline_for_stack
struct scrub_dev *scrub_setup_dev(struct btrfs_device *dev)
{
    struct scrub_dev *sdev;
    int     i;
    struct btrfs_fs_info *fs_info = dev->dev_root->fs_info;
    int pages_per_bio;

    pages_per_bio = min_t(int, SCRUB_PAGES_PER_BIO,
                  bio_get_nr_vecs(dev->bdev));
    sdev = kzalloc(sizeof(*sdev), GFP_NOFS);
    if (!sdev)
        goto nomem;
    sdev->dev = dev;
    sdev->pages_per_bio = pages_per_bio;
    sdev->curr = -1;
    for (i = 0; i < SCRUB_BIOS_PER_DEV; ++i) {
        struct scrub_bio *sbio;

        sbio = kzalloc(sizeof(*sbio), GFP_NOFS);
        if (!sbio)
            goto nomem;
        sdev->bios[i] = sbio;

        sbio->index = i;
        sbio->sdev = sdev;
        sbio->page_count = 0;
        sbio->work.func = scrub_bio_end_io_worker;

        if (i != SCRUB_BIOS_PER_DEV-1)
            sdev->bios[i]->next_free = i + 1;
        else
            sdev->bios[i]->next_free = -1;
    }
    sdev->first_free = 0;
    sdev->nodesize = dev->dev_root->nodesize;
    sdev->leafsize = dev->dev_root->leafsize;
    sdev->sectorsize = dev->dev_root->sectorsize;
    atomic_set(&sdev->in_flight, 0);
    atomic_set(&sdev->fixup_cnt, 0);
    atomic_set(&sdev->cancel_req, 0);
    sdev->csum_size = btrfs_super_csum_size(fs_info->super_copy);
    INIT_LIST_HEAD(&sdev->csum_list);

    spin_lock_init(&sdev->list_lock);
    spin_lock_init(&sdev->stat_lock);
    init_waitqueue_head(&sdev->list_wait);
    return sdev;

nomem:
    scrub_free_dev(sdev);
    return ERR_PTR(-ENOMEM);
}

static int scrub_print_warning_inode(u64 inum, u64 offset, u64 root, void *ctx)
{
    u64 isize;
    u32 nlink;
    int ret;
    int i;
    struct extent_buffer *eb;
    struct btrfs_inode_item *inode_item;
    struct scrub_warning *swarn = ctx;
    struct btrfs_fs_info *fs_info = swarn->dev->dev_root->fs_info;
    struct inode_fs_paths *ipath = NULL;
    struct btrfs_root *local_root;
    struct btrfs_key root_key;

    root_key.objectid = root;
    root_key.type = BTRFS_ROOT_ITEM_KEY;
    root_key.offset = (u64)-1;
    local_root = btrfs_read_fs_root_no_name(fs_info, &root_key);
    if (IS_ERR(local_root)) {
        ret = PTR_ERR(local_root);
        goto err;
    }

    ret = inode_item_info(inum, 0, local_root, swarn->path);
    if (ret) {
        btrfs_release_path(swarn->path);
        goto err;
    }

    eb = swarn->path->nodes[0];
    inode_item = btrfs_item_ptr(eb, swarn->path->slots[0],
                    struct btrfs_inode_item);
    isize = btrfs_inode_size(eb, inode_item);
    nlink = btrfs_inode_nlink(eb, inode_item);
    btrfs_release_path(swarn->path);

    ipath = init_ipath(4096, local_root, swarn->path);
    if (IS_ERR(ipath)) {
        ret = PTR_ERR(ipath);
        ipath = NULL;
        goto err;
    }
    ret = paths_from_inode(inum, ipath);

    if (ret < 0)
        goto err;

    /*
     * we deliberately ignore the bit ipath might have been too small to
     * hold all of the paths here
     */
    for (i = 0; i < ipath->fspath->elem_cnt; ++i)
        printk_in_rcu(KERN_WARNING "btrfs: %s at logical %llu on dev "
            "%s, sector %llu, root %llu, inode %llu, offset %llu, "
            "length %llu, links %u (path: %s)\n", swarn->errstr,
            swarn->logical, rcu_str_deref(swarn->dev->name),
            (unsigned long long)swarn->sector, root, inum, offset,
            min(isize - offset, (u64)PAGE_SIZE), nlink,
            (char *)(unsigned long)ipath->fspath->val[i]);

    free_ipath(ipath);
    return 0;

err:
    printk_in_rcu(KERN_WARNING "btrfs: %s at logical %llu on dev "
        "%s, sector %llu, root %llu, inode %llu, offset %llu: path "
        "resolving failed with ret=%d\n", swarn->errstr,
        swarn->logical, rcu_str_deref(swarn->dev->name),
        (unsigned long long)swarn->sector, root, inum, offset, ret);

    free_ipath(ipath);
    return 0;
}

static void scrub_print_warning(const char *errstr, struct scrub_block *sblock)
{
    struct btrfs_device *dev = sblock->sdev->dev;
    struct btrfs_fs_info *fs_info = dev->dev_root->fs_info;
    struct btrfs_path *path;
    struct btrfs_key found_key;
    struct extent_buffer *eb;
    struct btrfs_extent_item *ei;
    struct scrub_warning swarn;
    unsigned long ptr = 0;
    u64 extent_item_pos;
    u64 flags = 0;
    u64 ref_root;
    u32 item_size;
    u8 ref_level;
    const int bufsize = 4096;
    int ret;

    path = btrfs_alloc_path();

    swarn.scratch_buf = kmalloc(bufsize, GFP_NOFS);
    swarn.msg_buf = kmalloc(bufsize, GFP_NOFS);
    BUG_ON(sblock->page_count < 1);
    swarn.sector = (sblock->pagev[0].physical) >> 9;
    swarn.logical = sblock->pagev[0].logical;
    swarn.errstr = errstr;
    swarn.dev = dev;
    swarn.msg_bufsize = bufsize;
    swarn.scratch_bufsize = bufsize;

    if (!path || !swarn.scratch_buf || !swarn.msg_buf)
        goto out;

    ret = extent_from_logical(fs_info, swarn.logical, path, &found_key,
                  &flags);
    if (ret < 0)
        goto out;

    extent_item_pos = swarn.logical - found_key.objectid;
    swarn.extent_item_size = found_key.offset;

    eb = path->nodes[0];
    ei = btrfs_item_ptr(eb, path->slots[0], struct btrfs_extent_item);
    item_size = btrfs_item_size_nr(eb, path->slots[0]);
    btrfs_release_path(path);

    if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
        do {
            ret = tree_backref_for_extent(&ptr, eb, ei, item_size,
                            &ref_root, &ref_level);
            printk_in_rcu(KERN_WARNING
                "btrfs: %s at logical %llu on dev %s, "
                "sector %llu: metadata %s (level %d) in tree "
                "%llu\n", errstr, swarn.logical,
                rcu_str_deref(dev->name),
                (unsigned long long)swarn.sector,
                ref_level ? "node" : "leaf",
                ret < 0 ? -1 : ref_level,
                ret < 0 ? -1 : ref_root);
        } while (ret != 1);
    } else {
        swarn.path = path;
        iterate_extent_inodes(fs_info, found_key.objectid,
                    extent_item_pos, 1,
                    scrub_print_warning_inode, &swarn);
    }

out:
    btrfs_free_path(path);
    kfree(swarn.scratch_buf);
    kfree(swarn.msg_buf);
}

static int scrub_fixup_readpage(u64 inum, u64 offset, u64 root, void *ctx)
{
    struct page *page = NULL;
    unsigned long index;
    struct scrub_fixup_nodatasum *fixup = ctx;
    int ret;
    int corrected = 0;
    struct btrfs_key key;
    struct inode *inode = NULL;
    u64 end = offset + PAGE_SIZE - 1;
    struct btrfs_root *local_root;

    key.objectid = root;
    key.type = BTRFS_ROOT_ITEM_KEY;
    key.offset = (u64)-1;
    local_root = btrfs_read_fs_root_no_name(fixup->root->fs_info, &key);
    if (IS_ERR(local_root))
        return PTR_ERR(local_root);

    key.type = BTRFS_INODE_ITEM_KEY;
    key.objectid = inum;
    key.offset = 0;
    inode = btrfs_iget(fixup->root->fs_info->sb, &key, local_root, NULL);
    if (IS_ERR(inode))
        return PTR_ERR(inode);

    index = offset >> PAGE_CACHE_SHIFT;

    page = find_or_create_page(inode->i_mapping, index, GFP_NOFS);
    if (!page) {
        ret = -ENOMEM;
        goto out;
    }

    if (PageUptodate(page)) {
        struct btrfs_mapping_tree *map_tree;
        if (PageDirty(page)) {
            /*
             * we need to write the data to the defect sector. the
             * data that was in that sector is not in memory,
             * because the page was modified. we must not write the
             * modified page to that sector.
             *
             * TODO: what could be done here: wait for the delalloc
             *       runner to write out that page (might involve
             *       COW) and see whether the sector is still
             *       referenced afterwards.
             *
             * For the meantime, we'll treat this error
             * incorrectable, although there is a chance that a
             * later scrub will find the bad sector again and that
             * there's no dirty page in memory, then.
             */
            ret = -EIO;
            goto out;
        }
        map_tree = &BTRFS_I(inode)->root->fs_info->mapping_tree;
        ret = repair_io_failure(map_tree, offset, PAGE_SIZE,
                    fixup->logical, page,
                    fixup->mirror_num);
        unlock_page(page);
        corrected = !ret;
    } else {
        /*
         * we need to get good data first. the general readpage path
         * will call repair_io_failure for us, we just have to make
         * sure we read the bad mirror.
         */
        ret = set_extent_bits(&BTRFS_I(inode)->io_tree, offset, end,
                    EXTENT_DAMAGED, GFP_NOFS);
        if (ret) {
            /* set_extent_bits should give proper error */
            WARN_ON(ret > 0);
            if (ret > 0)
                ret = -EFAULT;
            goto out;
        }

        ret = extent_read_full_page(&BTRFS_I(inode)->io_tree, page,
                        btrfs_get_extent,
                        fixup->mirror_num);
        wait_on_page_locked(page);

        corrected = !test_range_bit(&BTRFS_I(inode)->io_tree, offset,
                        end, EXTENT_DAMAGED, 0, NULL);
        if (!corrected)
            clear_extent_bits(&BTRFS_I(inode)->io_tree, offset, end,
                        EXTENT_DAMAGED, GFP_NOFS);
    }

out:
    if (page)
        put_page(page);
    if (inode)
        iput(inode);

    if (ret < 0)
        return ret;

    if (ret == 0 && corrected) {
        /*
         * we only need to call readpage for one of the inodes belonging
         * to this extent. so make iterate_extent_inodes stop
         */
        return 1;
    }

    return -EIO;
}

static void scrub_fixup_nodatasum(struct btrfs_work *work)
{
    int ret;
    struct scrub_fixup_nodatasum *fixup;
    struct scrub_dev *sdev;
    struct btrfs_trans_handle *trans = NULL;
    struct btrfs_fs_info *fs_info;
    struct btrfs_path *path;
    int uncorrectable = 0;

    fixup = container_of(work, struct scrub_fixup_nodatasum, work);
    sdev = fixup->sdev;
    fs_info = fixup->root->fs_info;

    path = btrfs_alloc_path();
    if (!path) {
        spin_lock(&sdev->stat_lock);
        ++sdev->stat.malloc_errors;
        spin_unlock(&sdev->stat_lock);
        uncorrectable = 1;
        goto out;
    }

    trans = btrfs_join_transaction(fixup->root);
    if (IS_ERR(trans)) {
        uncorrectable = 1;
        goto out;
    }

    /*
     * the idea is to trigger a regular read through the standard path. we
     * read a page from the (failed) logical address by specifying the
     * corresponding copynum of the failed sector. thus, that readpage is
     * expected to fail.
     * that is the point where on-the-fly error correction will kick in
     * (once it's finished) and rewrite the failed sector if a good copy
     * can be found.
     */
    ret = iterate_inodes_from_logical(fixup->logical, fixup->root->fs_info,
                        path, scrub_fixup_readpage,
                        fixup);
    if (ret < 0) {
        uncorrectable = 1;
        goto out;
    }
    WARN_ON(ret != 1);

    spin_lock(&sdev->stat_lock);
    ++sdev->stat.corrected_errors;
    spin_unlock(&sdev->stat_lock);

out:
    if (trans && !IS_ERR(trans))
        btrfs_end_transaction(trans, fixup->root);
    if (uncorrectable) {
        spin_lock(&sdev->stat_lock);
        ++sdev->stat.uncorrectable_errors;
        spin_unlock(&sdev->stat_lock);

        printk_ratelimited_in_rcu(KERN_ERR
            "btrfs: unable to fixup (nodatasum) error at logical %llu on dev %s\n",
            (unsigned long long)fixup->logical,
            rcu_str_deref(sdev->dev->name));
    }

    btrfs_free_path(path);
    kfree(fixup);

    /* see caller why we're pretending to be paused in the scrub counters */
    mutex_lock(&fs_info->scrub_lock);
    atomic_dec(&fs_info->scrubs_running);
    atomic_dec(&fs_info->scrubs_paused);
    mutex_unlock(&fs_info->scrub_lock);
    atomic_dec(&sdev->fixup_cnt);
    wake_up(&fs_info->scrub_pause_wait);
    wake_up(&sdev->list_wait);
}

/*
 * scrub_handle_errored_block gets called when either verification of the
 * pages failed or the bio failed to read, e.g. with EIO. In the latter
 * case, this function handles all pages in the bio, even though only one
 * may be bad.
 * The goal of this function is to repair the errored block by using the
 * contents of one of the mirrors.
 */
static int scrub_handle_errored_block(struct scrub_block *sblock_to_check)
{
    struct scrub_dev *sdev = sblock_to_check->sdev;
    struct btrfs_fs_info *fs_info;
    u64 length;
    u64 logical;
    u64 generation;
    unsigned int failed_mirror_index;
    unsigned int is_metadata;
    unsigned int have_csum;
    u8 *csum;
    struct scrub_block *sblocks_for_recheck; /* holds one for each mirror */
    struct scrub_block *sblock_bad;
    int ret;
    int mirror_index;
    int page_num;
    int success;
    static DEFINE_RATELIMIT_STATE(_rs, DEFAULT_RATELIMIT_INTERVAL,
                      DEFAULT_RATELIMIT_BURST);

    BUG_ON(sblock_to_check->page_count < 1);
    fs_info = sdev->dev->dev_root->fs_info;
    length = sblock_to_check->page_count * PAGE_SIZE;
    logical = sblock_to_check->pagev[0].logical;
    generation = sblock_to_check->pagev[0].generation;
    BUG_ON(sblock_to_check->pagev[0].mirror_num < 1);
    failed_mirror_index = sblock_to_check->pagev[0].mirror_num - 1;
    is_metadata = !(sblock_to_check->pagev[0].flags &
            BTRFS_EXTENT_FLAG_DATA);
    have_csum = sblock_to_check->pagev[0].have_csum;
    csum = sblock_to_check->pagev[0].csum;

    /*
     * read all mirrors one after the other. This includes to
     * re-read the extent or metadata block that failed (that was
     * the cause that this fixup code is called) another time,
     * page by page this time in order to know which pages
     * caused I/O errors and which ones are good (for all mirrors).
     * It is the goal to handle the situation when more than one
     * mirror contains I/O errors, but the errors do not
     * overlap, i.e. the data can be repaired by selecting the
     * pages from those mirrors without I/O error on the
     * particular pages. One example (with blocks >= 2 * PAGE_SIZE)
     * would be that mirror #1 has an I/O error on the first page,
     * the second page is good, and mirror #2 has an I/O error on
     * the second page, but the first page is good.
     * Then the first page of the first mirror can be repaired by
     * taking the first page of the second mirror, and the
     * second page of the second mirror can be repaired by
     * copying the contents of the 2nd page of the 1st mirror.
     * One more note: if the pages of one mirror contain I/O
     * errors, the checksum cannot be verified. In order to get
     * the best data for repairing, the first attempt is to find
     * a mirror without I/O errors and with a validated checksum.
     * Only if this is not possible, the pages are picked from
     * mirrors with I/O errors without considering the checksum.
     * If the latter is the case, at the end, the checksum of the
     * repaired area is verified in order to correctly maintain
     * the statistics.
     */

    sblocks_for_recheck = kzalloc(BTRFS_MAX_MIRRORS *
                     sizeof(*sblocks_for_recheck),
                     GFP_NOFS);
    if (!sblocks_for_recheck) {
        spin_lock(&sdev->stat_lock);
        sdev->stat.malloc_errors++;
        sdev->stat.read_errors++;
        sdev->stat.uncorrectable_errors++;
        spin_unlock(&sdev->stat_lock);
        btrfs_dev_stat_inc_and_print(sdev->dev,
                         BTRFS_DEV_STAT_READ_ERRS);
        goto out;
    }

    /* setup the context, map the logical blocks and alloc the pages */
    ret = scrub_setup_recheck_block(sdev, &fs_info->mapping_tree, length,
                    logical, sblocks_for_recheck);
    if (ret) {
        spin_lock(&sdev->stat_lock);
        sdev->stat.read_errors++;
        sdev->stat.uncorrectable_errors++;
        spin_unlock(&sdev->stat_lock);
        btrfs_dev_stat_inc_and_print(sdev->dev,
                         BTRFS_DEV_STAT_READ_ERRS);
        goto out;
    }
    BUG_ON(failed_mirror_index >= BTRFS_MAX_MIRRORS);
    sblock_bad = sblocks_for_recheck + failed_mirror_index;

    /* build and submit the bios for the failed mirror, check checksums */
    ret = scrub_recheck_block(fs_info, sblock_bad, is_metadata, have_csum,
                  csum, generation, sdev->csum_size);
    if (ret) {
        spin_lock(&sdev->stat_lock);
        sdev->stat.read_errors++;
        sdev->stat.uncorrectable_errors++;
        spin_unlock(&sdev->stat_lock);
        btrfs_dev_stat_inc_and_print(sdev->dev,
                         BTRFS_DEV_STAT_READ_ERRS);
        goto out;
    }

    if (!sblock_bad->header_error && !sblock_bad->checksum_error &&
        sblock_bad->no_io_error_seen) {
        /*
         * the error disappeared after reading page by page, or
         * the area was part of a huge bio and other parts of the
         * bio caused I/O errors, or the block layer merged several
         * read requests into one and the error is caused by a
         * different bio (usually one of the two latter cases is
         * the cause)
         */
        spin_lock(&sdev->stat_lock);
        sdev->stat.unverified_errors++;
        spin_unlock(&sdev->stat_lock);

        goto out;
    }

    if (!sblock_bad->no_io_error_seen) {
        spin_lock(&sdev->stat_lock);
        sdev->stat.read_errors++;
        spin_unlock(&sdev->stat_lock);
        if (__ratelimit(&_rs))
            scrub_print_warning("i/o error", sblock_to_check);
        btrfs_dev_stat_inc_and_print(sdev->dev,
                         BTRFS_DEV_STAT_READ_ERRS);
    } else if (sblock_bad->checksum_error) {
        spin_lock(&sdev->stat_lock);
        sdev->stat.csum_errors++;
        spin_unlock(&sdev->stat_lock);
        if (__ratelimit(&_rs))
            scrub_print_warning("checksum error", sblock_to_check);
        btrfs_dev_stat_inc_and_print(sdev->dev,
                         BTRFS_DEV_STAT_CORRUPTION_ERRS);
    } else if (sblock_bad->header_error) {
        spin_lock(&sdev->stat_lock);
        sdev->stat.verify_errors++;
        spin_unlock(&sdev->stat_lock);
        if (__ratelimit(&_rs))
            scrub_print_warning("checksum/header error",
                        sblock_to_check);
        if (sblock_bad->generation_error)
            btrfs_dev_stat_inc_and_print(sdev->dev,
                BTRFS_DEV_STAT_GENERATION_ERRS);
        else
            btrfs_dev_stat_inc_and_print(sdev->dev,
                BTRFS_DEV_STAT_CORRUPTION_ERRS);
    }

    if (sdev->readonly)
        goto did_not_correct_error;

    if (!is_metadata && !have_csum) {
        struct scrub_fixup_nodatasum *fixup_nodatasum;

        /*
         * !is_metadata and !have_csum, this means that the data
         * might not be COW'ed, that it might be modified
         * concurrently. The general strategy to work on the
         * commit root does not help in the case when COW is not
         * used.
         */
        fixup_nodatasum = kzalloc(sizeof(*fixup_nodatasum), GFP_NOFS);
        if (!fixup_nodatasum)
            goto did_not_correct_error;
        fixup_nodatasum->sdev = sdev;
        fixup_nodatasum->logical = logical;
        fixup_nodatasum->root = fs_info->extent_root;
        fixup_nodatasum->mirror_num = failed_mirror_index + 1;
        /*
         * increment scrubs_running to prevent cancel requests from
         * completing as long as a fixup worker is running. we must also
         * increment scrubs_paused to prevent deadlocking on pause
         * requests used for transactions commits (as the worker uses a
         * transaction context). it is safe to regard the fixup worker
         * as paused for all matters practical. effectively, we only
         * avoid cancellation requests from completing.
         */
        mutex_lock(&fs_info->scrub_lock);
        atomic_inc(&fs_info->scrubs_running);
        atomic_inc(&fs_info->scrubs_paused);
        mutex_unlock(&fs_info->scrub_lock);
        atomic_inc(&sdev->fixup_cnt);
        fixup_nodatasum->work.func = scrub_fixup_nodatasum;
        btrfs_queue_worker(&fs_info->scrub_workers,
                   &fixup_nodatasum->work);
        goto out;
    }

    /*
     * now build and submit the bios for the other mirrors, check
     * checksums
     */
    for (mirror_index = 0;
         mirror_index < BTRFS_MAX_MIRRORS &&
         sblocks_for_recheck[mirror_index].page_count > 0;
         mirror_index++) {
        if (mirror_index == failed_mirror_index)
            continue;

        /* build and submit the bios, check checksums */
        ret = scrub_recheck_block(fs_info,
                      sblocks_for_recheck + mirror_index,
                      is_metadata, have_csum, csum,
                      generation, sdev->csum_size);
        if (ret)
            goto did_not_correct_error;
    }

    /*
     * first try to pick the mirror which is completely without I/O
     * errors and also does not have a checksum error.
     * If one is found, and if a checksum is present, the full block
     * that is known to contain an error is rewritten. Afterwards
     * the block is known to be corrected.
     * If a mirror is found which is completely correct, and no
     * checksum is present, only those pages are rewritten that had
     * an I/O error in the block to be repaired, since it cannot be
     * determined, which copy of the other pages is better (and it
     * could happen otherwise that a correct page would be
     * overwritten by a bad one).
     */
    for (mirror_index = 0;
         mirror_index < BTRFS_MAX_MIRRORS &&
         sblocks_for_recheck[mirror_index].page_count > 0;
         mirror_index++) {
        struct scrub_block *sblock_other = sblocks_for_recheck +
                           mirror_index;

        if (!sblock_other->header_error &&
            !sblock_other->checksum_error &&
            sblock_other->no_io_error_seen) {
            int force_write = is_metadata || have_csum;

            ret = scrub_repair_block_from_good_copy(sblock_bad,
                                sblock_other,
                                force_write);
            if (0 == ret)
                goto corrected_error;
        }
    }

    /*
     * in case of I/O errors in the area that is supposed to be
     * repaired, continue by picking good copies of those pages.
     * Select the good pages from mirrors to rewrite bad pages from
     * the area to fix. Afterwards verify the checksum of the block
     * that is supposed to be repaired. This verification step is
     * only done for the purpose of statistic counting and for the
     * final scrub report, whether errors remain.
     * A perfect algorithm could make use of the checksum and try
     * all possible combinations of pages from the different mirrors
     * until the checksum verification succeeds. For example, when
     * the 2nd page of mirror #1 faces I/O errors, and the 2nd page
     * of mirror #2 is readable but the final checksum test fails,
     * then the 2nd page of mirror #3 could be tried, whether now
     * the final checksum succeedes. But this would be a rare
     * exception and is therefore not implemented. At least it is
     * avoided that the good copy is overwritten.
     * A more useful improvement would be to pick the sectors
     * without I/O error based on sector sizes (512 bytes on legacy
     * disks) instead of on PAGE_SIZE. Then maybe 512 byte of one
     * mirror could be repaired by taking 512 byte of a different
     * mirror, even if other 512 byte sectors in the same PAGE_SIZE
     * area are unreadable.
     */

    /* can only fix I/O errors from here on */
    if (sblock_bad->no_io_error_seen)
        goto did_not_correct_error;

    success = 1;
    for (page_num = 0; page_num < sblock_bad->page_count; page_num++) {
        struct scrub_page *page_bad = sblock_bad->pagev + page_num;

        if (!page_bad->io_error)
            continue;

        for (mirror_index = 0;
             mirror_index < BTRFS_MAX_MIRRORS &&
             sblocks_for_recheck[mirror_index].page_count > 0;
             mirror_index++) {
            struct scrub_block *sblock_other = sblocks_for_recheck +
                               mirror_index;
            struct scrub_page *page_other = sblock_other->pagev +
                            page_num;

            if (!page_other->io_error) {
                ret = scrub_repair_page_from_good_copy(
                    sblock_bad, sblock_other, page_num, 0);
                if (0 == ret) {
                    page_bad->io_error = 0;
                    break; /* succeeded for this page */
                }
            }
        }

        if (page_bad->io_error) {
            /* did not find a mirror to copy the page from */
            success = 0;
        }
    }

    if (success) {
        if (is_metadata || have_csum) {
            /*
             * need to verify the checksum now that all
             * sectors on disk are repaired (the write
             * request for data to be repaired is on its way).
             * Just be lazy and use scrub_recheck_block()
             * which re-reads the data before the checksum
             * is verified, but most likely the data comes out
             * of the page cache.
             */
            ret = scrub_recheck_block(fs_info, sblock_bad,
                          is_metadata, have_csum, csum,
                          generation, sdev->csum_size);
            if (!ret && !sblock_bad->header_error &&
                !sblock_bad->checksum_error &&
                sblock_bad->no_io_error_seen)
                goto corrected_error;
            else
                goto did_not_correct_error;
        } else {
corrected_error:
            spin_lock(&sdev->stat_lock);
            sdev->stat.corrected_errors++;
            spin_unlock(&sdev->stat_lock);
            printk_ratelimited_in_rcu(KERN_ERR
                "btrfs: fixed up error at logical %llu on dev %s\n",
                (unsigned long long)logical,
                rcu_str_deref(sdev->dev->name));
        }
    } else {
did_not_correct_error:
        spin_lock(&sdev->stat_lock);
        sdev->stat.uncorrectable_errors++;
        spin_unlock(&sdev->stat_lock);
        printk_ratelimited_in_rcu(KERN_ERR
            "btrfs: unable to fixup (regular) error at logical %llu on dev %s\n",
            (unsigned long long)logical,
            rcu_str_deref(sdev->dev->name));
    }

out:
    if (sblocks_for_recheck) {
        for (mirror_index = 0; mirror_index < BTRFS_MAX_MIRRORS;
             mirror_index++) {
            struct scrub_block *sblock = sblocks_for_recheck +
                             mirror_index;
            int page_index;

            for (page_index = 0; page_index < SCRUB_PAGES_PER_BIO;
                 page_index++)
                if (sblock->pagev[page_index].page)
                    __free_page(
                        sblock->pagev[page_index].page);
        }
        kfree(sblocks_for_recheck);
    }

    return 0;
}

static int scrub_setup_recheck_block(struct scrub_dev *sdev,
                     struct btrfs_mapping_tree *map_tree,
                     u64 length, u64 logical,
                     struct scrub_block *sblocks_for_recheck)
{
    int page_index;
    int mirror_index;
    int ret;

    /*
     * note: the three members sdev, ref_count and outstanding_pages
     * are not used (and not set) in the blocks that are used for
     * the recheck procedure
     */

    page_index = 0;
    while (length > 0) {
        u64 sublen = min_t(u64, length, PAGE_SIZE);
        u64 mapped_length = sublen;
        struct btrfs_bio *bbio = NULL;

        /*
         * with a length of PAGE_SIZE, each returned stripe
         * represents one mirror
         */
        ret = btrfs_map_block(map_tree, WRITE, logical, &mapped_length,
                      &bbio, 0);
        if (ret || !bbio || mapped_length < sublen) {
            kfree(bbio);
            return -EIO;
        }

        BUG_ON(page_index >= SCRUB_PAGES_PER_BIO);
        for (mirror_index = 0; mirror_index < (int)bbio->num_stripes;
             mirror_index++) {
            struct scrub_block *sblock;
            struct scrub_page *page;

            if (mirror_index >= BTRFS_MAX_MIRRORS)
                continue;

            sblock = sblocks_for_recheck + mirror_index;
            page = sblock->pagev + page_index;
            page->logical = logical;
            page->physical = bbio->stripes[mirror_index].physical;
            /* for missing devices, dev->bdev is NULL */
            page->dev = bbio->stripes[mirror_index].dev;
            page->mirror_num = mirror_index + 1;
            page->page = alloc_page(GFP_NOFS);
            if (!page->page) {
                spin_lock(&sdev->stat_lock);
                sdev->stat.malloc_errors++;
                spin_unlock(&sdev->stat_lock);
                kfree(bbio);
                return -ENOMEM;
            }
            sblock->page_count++;
        }
        kfree(bbio);
        length -= sublen;
        logical += sublen;
        page_index++;
    }

    return 0;
}

/*
 * this function will check the on disk data for checksum errors, header
 * errors and read I/O errors. If any I/O errors happen, the exact pages
 * which are errored are marked as being bad. The goal is to enable scrub
 * to take those pages that are not errored from all the mirrors so that
 * the pages that are errored in the just handled mirror can be repaired.
 */
static int scrub_recheck_block(struct btrfs_fs_info *fs_info,
                   struct scrub_block *sblock, int is_metadata,
                   int have_csum, u8 *csum, u64 generation,
                   u16 csum_size)
{
    int page_num;

    sblock->no_io_error_seen = 1;
    sblock->header_error = 0;
    sblock->checksum_error = 0;

    for (page_num = 0; page_num < sblock->page_count; page_num++) {
        struct bio *bio;
        int ret;
        struct scrub_page *page = sblock->pagev + page_num;
        DECLARE_COMPLETION_ONSTACK(complete);

        if (page->dev->bdev == NULL) {
            page->io_error = 1;
            sblock->no_io_error_seen = 0;
            continue;
        }

        BUG_ON(!page->page);
        bio = bio_alloc(GFP_NOFS, 1);
        if (!bio)
            return -EIO;
        bio->bi_bdev = page->dev->bdev;
        bio->bi_sector = page->physical >> 9;
        bio->bi_end_io = scrub_complete_bio_end_io;
        bio->bi_private = &complete;

        ret = bio_add_page(bio, page->page, PAGE_SIZE, 0);
        if (PAGE_SIZE != ret) {
            bio_put(bio);
            return -EIO;
        }
        btrfsic_submit_bio(READ, bio);

        /* this will also unplug the queue */
        wait_for_completion(&complete);

        page->io_error = !test_bit(BIO_UPTODATE, &bio->bi_flags);
        if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
            sblock->no_io_error_seen = 0;
        bio_put(bio);
    }

    if (sblock->no_io_error_seen)
        scrub_recheck_block_checksum(fs_info, sblock, is_metadata,
                         have_csum, csum, generation,
                         csum_size);

    return 0;
}

static void scrub_recheck_block_checksum(struct btrfs_fs_info *fs_info,
                     struct scrub_block *sblock,
                     int is_metadata, int have_csum,
                     const u8 *csum, u64 generation,
                     u16 csum_size)
{
    int page_num;
    u8 calculated_csum[BTRFS_CSUM_SIZE];
    u32 crc = ~(u32)0;
    struct btrfs_root *root = fs_info->extent_root;
    void *mapped_buffer;

    BUG_ON(!sblock->pagev[0].page);
    if (is_metadata) {
        struct btrfs_header *h;

        mapped_buffer = kmap_atomic(sblock->pagev[0].page);
        h = (struct btrfs_header *)mapped_buffer;

        if (sblock->pagev[0].logical != le64_to_cpu(h->bytenr) ||
            memcmp(h->fsid, fs_info->fsid, BTRFS_UUID_SIZE) ||
            memcmp(h->chunk_tree_uuid, fs_info->chunk_tree_uuid,
               BTRFS_UUID_SIZE)) {
            sblock->header_error = 1;
        } else if (generation != le64_to_cpu(h->generation)) {
            sblock->header_error = 1;
            sblock->generation_error = 1;
        }
        csum = h->csum;
    } else {
        if (!have_csum)
            return;

        mapped_buffer = kmap_atomic(sblock->pagev[0].page);
    }

    for (page_num = 0;;) {
        if (page_num == 0 && is_metadata)
            crc = btrfs_csum_data(root,
                ((u8 *)mapped_buffer) + BTRFS_CSUM_SIZE,
                crc, PAGE_SIZE - BTRFS_CSUM_SIZE);
        else
            crc = btrfs_csum_data(root, mapped_buffer, crc,
                          PAGE_SIZE);

        kunmap_atomic(mapped_buffer);
        page_num++;
        if (page_num >= sblock->page_count)
            break;
        BUG_ON(!sblock->pagev[page_num].page);

        mapped_buffer = kmap_atomic(sblock->pagev[page_num].page);
    }

    btrfs_csum_final(crc, calculated_csum);
    if (memcmp(calculated_csum, csum, csum_size))
        sblock->checksum_error = 1;
}

static void scrub_complete_bio_end_io(struct bio *bio, int err)
{
    complete((struct completion *)bio->bi_private);
}

static int scrub_repair_block_from_good_copy(struct scrub_block *sblock_bad,
                         struct scrub_block *sblock_good,
                         int force_write)
{
    int page_num;
    int ret = 0;

    for (page_num = 0; page_num < sblock_bad->page_count; page_num++) {
        int ret_sub;

        ret_sub = scrub_repair_page_from_good_copy(sblock_bad,
                               sblock_good,
                               page_num,
                               force_write);
        if (ret_sub)
            ret = ret_sub;
    }

    return ret;
}

static int scrub_repair_page_from_good_copy(struct scrub_block *sblock_bad,
                        struct scrub_block *sblock_good,
                        int page_num, int force_write)
{
    struct scrub_page *page_bad = sblock_bad->pagev + page_num;
    struct scrub_page *page_good = sblock_good->pagev + page_num;

    BUG_ON(sblock_bad->pagev[page_num].page == NULL);
    BUG_ON(sblock_good->pagev[page_num].page == NULL);
    if (force_write || sblock_bad->header_error ||
        sblock_bad->checksum_error || page_bad->io_error) {
        struct bio *bio;
        int ret;
        DECLARE_COMPLETION_ONSTACK(complete);

        bio = bio_alloc(GFP_NOFS, 1);
        if (!bio)
            return -EIO;
        bio->bi_bdev = page_bad->dev->bdev;
        bio->bi_sector = page_bad->physical >> 9;
        bio->bi_end_io = scrub_complete_bio_end_io;
        bio->bi_private = &complete;

        ret = bio_add_page(bio, page_good->page, PAGE_SIZE, 0);
        if (PAGE_SIZE != ret) {
            bio_put(bio);
            return -EIO;
        }
        btrfsic_submit_bio(WRITE, bio);

        /* this will also unplug the queue */
        wait_for_completion(&complete);
        if (!bio_flagged(bio, BIO_UPTODATE)) {
            btrfs_dev_stat_inc_and_print(page_bad->dev,
                BTRFS_DEV_STAT_WRITE_ERRS);
            bio_put(bio);
            return -EIO;
        }
        bio_put(bio);
    }

    return 0;
}

static void scrub_checksum(struct scrub_block *sblock)
{
    u64 flags;
    int ret;

    BUG_ON(sblock->page_count < 1);
    flags = sblock->pagev[0].flags;
    ret = 0;
    if (flags & BTRFS_EXTENT_FLAG_DATA)
        ret = scrub_checksum_data(sblock);
    else if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)
        ret = scrub_checksum_tree_block(sblock);
    else if (flags & BTRFS_EXTENT_FLAG_SUPER)
        (void)scrub_checksum_super(sblock);
    else
        WARN_ON(1);
    if (ret)
        scrub_handle_errored_block(sblock);
}

static int scrub_checksum_data(struct scrub_block *sblock)
{
    struct scrub_dev *sdev = sblock->sdev;
    u8 csum[BTRFS_CSUM_SIZE];
    u8 *on_disk_csum;
    struct page *page;
    void *buffer;
    u32 crc = ~(u32)0;
    int fail = 0;
    struct btrfs_root *root = sdev->dev->dev_root;
    u64 len;
    int index;

    BUG_ON(sblock->page_count < 1);
    if (!sblock->pagev[0].have_csum)
        return 0;

    on_disk_csum = sblock->pagev[0].csum;
    page = sblock->pagev[0].page;
    buffer = kmap_atomic(page);

    len = sdev->sectorsize;
    index = 0;
    for (;;) {
        u64 l = min_t(u64, len, PAGE_SIZE);

        crc = btrfs_csum_data(root, buffer, crc, l);
        kunmap_atomic(buffer);
        len -= l;
        if (len == 0)
            break;
        index++;
        BUG_ON(index >= sblock->page_count);
        BUG_ON(!sblock->pagev[index].page);
        page = sblock->pagev[index].page;
        buffer = kmap_atomic(page);
    }

    btrfs_csum_final(crc, csum);
    if (memcmp(csum, on_disk_csum, sdev->csum_size))
        fail = 1;

    return fail;
}

static int scrub_checksum_tree_block(struct scrub_block *sblock)
{
    struct scrub_dev *sdev = sblock->sdev;
    struct btrfs_header *h;
    struct btrfs_root *root = sdev->dev->dev_root;
    struct btrfs_fs_info *fs_info = root->fs_info;
    u8 calculated_csum[BTRFS_CSUM_SIZE];
    u8 on_disk_csum[BTRFS_CSUM_SIZE];
    struct page *page;
    void *mapped_buffer;
    u64 mapped_size;
    void *p;
    u32 crc = ~(u32)0;
    int fail = 0;
    int crc_fail = 0;
    u64 len;
    int index;

    BUG_ON(sblock->page_count < 1);
    page = sblock->pagev[0].page;
    mapped_buffer = kmap_atomic(page);
    h = (struct btrfs_header *)mapped_buffer;
    memcpy(on_disk_csum, h->csum, sdev->csum_size);

    /*
     * we don't use the getter functions here, as we
     * a) don't have an extent buffer and
     * b) the page is already kmapped
     */

    if (sblock->pagev[0].logical != le64_to_cpu(h->bytenr))
        ++fail;

    if (sblock->pagev[0].generation != le64_to_cpu(h->generation))
        ++fail;

    if (memcmp(h->fsid, fs_info->fsid, BTRFS_UUID_SIZE))
        ++fail;

    if (memcmp(h->chunk_tree_uuid, fs_info->chunk_tree_uuid,
           BTRFS_UUID_SIZE))
        ++fail;

    BUG_ON(sdev->nodesize != sdev->leafsize);
    len = sdev->nodesize - BTRFS_CSUM_SIZE;
    mapped_size = PAGE_SIZE - BTRFS_CSUM_SIZE;
    p = ((u8 *)mapped_buffer) + BTRFS_CSUM_SIZE;
    index = 0;
    for (;;) {
        u64 l = min_t(u64, len, mapped_size);

        crc = btrfs_csum_data(root, p, crc, l);
        kunmap_atomic(mapped_buffer);
        len -= l;
        if (len == 0)
            break;
        index++;
        BUG_ON(index >= sblock->page_count);
        BUG_ON(!sblock->pagev[index].page);
        page = sblock->pagev[index].page;
        mapped_buffer = kmap_atomic(page);
        mapped_size = PAGE_SIZE;
        p = mapped_buffer;
    }

    btrfs_csum_final(crc, calculated_csum);
    if (memcmp(calculated_csum, on_disk_csum, sdev->csum_size))
        ++crc_fail;

    return fail || crc_fail;
}

static int scrub_checksum_super(struct scrub_block *sblock)
{
    struct btrfs_super_block *s;
    struct scrub_dev *sdev = sblock->sdev;
    struct btrfs_root *root = sdev->dev->dev_root;
    struct btrfs_fs_info *fs_info = root->fs_info;
    u8 calculated_csum[BTRFS_CSUM_SIZE];
    u8 on_disk_csum[BTRFS_CSUM_SIZE];
    struct page *page;
    void *mapped_buffer;
    u64 mapped_size;
    void *p;
    u32 crc = ~(u32)0;
    int fail_gen = 0;
    int fail_cor = 0;
    u64 len;
    int index;

    BUG_ON(sblock->page_count < 1);
    page = sblock->pagev[0].page;
    mapped_buffer = kmap_atomic(page);
    s = (struct btrfs_super_block *)mapped_buffer;
    memcpy(on_disk_csum, s->csum, sdev->csum_size);

    if (sblock->pagev[0].logical != le64_to_cpu(s->bytenr))
        ++fail_cor;

    if (sblock->pagev[0].generation != le64_to_cpu(s->generation))
        ++fail_gen;

    if (memcmp(s->fsid, fs_info->fsid, BTRFS_UUID_SIZE))
        ++fail_cor;

    len = BTRFS_SUPER_INFO_SIZE - BTRFS_CSUM_SIZE;
    mapped_size = PAGE_SIZE - BTRFS_CSUM_SIZE;
    p = ((u8 *)mapped_buffer) + BTRFS_CSUM_SIZE;
    index = 0;
    for (;;) {
        u64 l = min_t(u64, len, mapped_size);

        crc = btrfs_csum_data(root, p, crc, l);
        kunmap_atomic(mapped_buffer);
        len -= l;
        if (len == 0)
            break;
        index++;
        BUG_ON(index >= sblock->page_count);
        BUG_ON(!sblock->pagev[index].page);
        page = sblock->pagev[index].page;
        mapped_buffer = kmap_atomic(page);
        mapped_size = PAGE_SIZE;
        p = mapped_buffer;
    }

    btrfs_csum_final(crc, calculated_csum);
    if (memcmp(calculated_csum, on_disk_csum, sdev->csum_size))
        ++fail_cor;

    if (fail_cor + fail_gen) {
        /*
         * if we find an error in a super block, we just report it.
         * They will get written with the next transaction commit
         * anyway
         */
        spin_lock(&sdev->stat_lock);
        ++sdev->stat.super_errors;
        spin_unlock(&sdev->stat_lock);
        if (fail_cor)
            btrfs_dev_stat_inc_and_print(sdev->dev,
                BTRFS_DEV_STAT_CORRUPTION_ERRS);
        else
            btrfs_dev_stat_inc_and_print(sdev->dev,
                BTRFS_DEV_STAT_GENERATION_ERRS);
    }

    return fail_cor + fail_gen;
}

static void scrub_block_get(struct scrub_block *sblock)
{
    atomic_inc(&sblock->ref_count);
}

static void scrub_block_put(struct scrub_block *sblock)
{
    if (atomic_dec_and_test(&sblock->ref_count)) {
        int i;

        for (i = 0; i < sblock->page_count; i++)
            if (sblock->pagev[i].page)
                __free_page(sblock->pagev[i].page);
        kfree(sblock);
    }
}

static void scrub_submit(struct scrub_dev *sdev)
{
    struct scrub_bio *sbio;

    if (sdev->curr == -1)
        return;

    sbio = sdev->bios[sdev->curr];
    sdev->curr = -1;
    atomic_inc(&sdev->in_flight);

    btrfsic_submit_bio(READ, sbio->bio);
}

static int scrub_add_page_to_bio(struct scrub_dev *sdev,
                 struct scrub_page *spage)
{
    struct scrub_block *sblock = spage->sblock;
    struct scrub_bio *sbio;
    int ret;

again:
    /*
     * grab a fresh bio or wait for one to become available
     */
    while (sdev->curr == -1) {
        spin_lock(&sdev->list_lock);
        sdev->curr = sdev->first_free;
        if (sdev->curr != -1) {
            sdev->first_free = sdev->bios[sdev->curr]->next_free;
            sdev->bios[sdev->curr]->next_free = -1;
            sdev->bios[sdev->curr]->page_count = 0;
            spin_unlock(&sdev->list_lock);
        } else {
            spin_unlock(&sdev->list_lock);
            wait_event(sdev->list_wait, sdev->first_free != -1);
        }
    }
    sbio = sdev->bios[sdev->curr];
    if (sbio->page_count == 0) {
        struct bio *bio;

        sbio->physical = spage->physical;
        sbio->logical = spage->logical;
        bio = sbio->bio;
        if (!bio) {
            bio = bio_alloc(GFP_NOFS, sdev->pages_per_bio);
            if (!bio)
                return -ENOMEM;
            sbio->bio = bio;
        }

        bio->bi_private = sbio;
        bio->bi_end_io = scrub_bio_end_io;
        bio->bi_bdev = sdev->dev->bdev;
        bio->bi_sector = spage->physical >> 9;
        sbio->err = 0;
    } else if (sbio->physical + sbio->page_count * PAGE_SIZE !=
           spage->physical ||
           sbio->logical + sbio->page_count * PAGE_SIZE !=
           spage->logical) {
        scrub_submit(sdev);
        goto again;
    }

    sbio->pagev[sbio->page_count] = spage;
    ret = bio_add_page(sbio->bio, spage->page, PAGE_SIZE, 0);
    if (ret != PAGE_SIZE) {
        if (sbio->page_count < 1) {
            bio_put(sbio->bio);
            sbio->bio = NULL;
            return -EIO;
        }
        scrub_submit(sdev);
        goto again;
    }

    scrub_block_get(sblock); /* one for the added page */
    atomic_inc(&sblock->outstanding_pages);
    sbio->page_count++;
    if (sbio->page_count == sdev->pages_per_bio)
        scrub_submit(sdev);

    return 0;
}

static int scrub_pages(struct scrub_dev *sdev, u64 logical, u64 len,
               u64 physical, u64 flags, u64 gen, int mirror_num,
               u8 *csum, int force)
{
    struct scrub_block *sblock;
    int index;

    sblock = kzalloc(sizeof(*sblock), GFP_NOFS);
    if (!sblock) {
        spin_lock(&sdev->stat_lock);
        sdev->stat.malloc_errors++;
        spin_unlock(&sdev->stat_lock);
        return -ENOMEM;
    }

    /* one ref inside this function, plus one for each page later on */
    atomic_set(&sblock->ref_count, 1);
    sblock->sdev = sdev;
    sblock->no_io_error_seen = 1;

    for (index = 0; len > 0; index++) {
        struct scrub_page *spage = sblock->pagev + index;
        u64 l = min_t(u64, len, PAGE_SIZE);

        BUG_ON(index >= SCRUB_MAX_PAGES_PER_BLOCK);
        spage->page = alloc_page(GFP_NOFS);
        if (!spage->page) {
            spin_lock(&sdev->stat_lock);
            sdev->stat.malloc_errors++;
            spin_unlock(&sdev->stat_lock);
            while (index > 0) {
                index--;
                __free_page(sblock->pagev[index].page);
            }
            kfree(sblock);
            return -ENOMEM;
        }
        spage->sblock = sblock;
        spage->dev = sdev->dev;
        spage->flags = flags;
        spage->generation = gen;
        spage->logical = logical;
        spage->physical = physical;
        spage->mirror_num = mirror_num;
        if (csum) {
            spage->have_csum = 1;
            memcpy(spage->csum, csum, sdev->csum_size);
        } else {
            spage->have_csum = 0;
        }
        sblock->page_count++;
        len -= l;
        logical += l;
        physical += l;
    }

    BUG_ON(sblock->page_count == 0);
    for (index = 0; index < sblock->page_count; index++) {
        struct scrub_page *spage = sblock->pagev + index;
        int ret;

        ret = scrub_add_page_to_bio(sdev, spage);
        if (ret) {
            scrub_block_put(sblock);
            return ret;
        }
    }

    if (force)
        scrub_submit(sdev);

    /* last one frees, either here or in bio completion for last page */
    scrub_block_put(sblock);
    return 0;
}

static void scrub_bio_end_io(struct bio *bio, int err)
{
    struct scrub_bio *sbio = bio->bi_private;
    struct scrub_dev *sdev = sbio->sdev;
    struct btrfs_fs_info *fs_info = sdev->dev->dev_root->fs_info;

    sbio->err = err;
    sbio->bio = bio;

    btrfs_queue_worker(&fs_info->scrub_workers, &sbio->work);
}

static void scrub_bio_end_io_worker(struct btrfs_work *work)
{
    struct scrub_bio *sbio = container_of(work, struct scrub_bio, work);
    struct scrub_dev *sdev = sbio->sdev;
    int i;

    BUG_ON(sbio->page_count > SCRUB_PAGES_PER_BIO);
    if (sbio->err) {
        for (i = 0; i < sbio->page_count; i++) {
            struct scrub_page *spage = sbio->pagev[i];

            spage->io_error = 1;
            spage->sblock->no_io_error_seen = 0;
        }
    }

    /* now complete the scrub_block items that have all pages completed */
    for (i = 0; i < sbio->page_count; i++) {
        struct scrub_page *spage = sbio->pagev[i];
        struct scrub_block *sblock = spage->sblock;

        if (atomic_dec_and_test(&sblock->outstanding_pages))
            scrub_block_complete(sblock);
        scrub_block_put(sblock);
    }

    bio_put(sbio->bio);
    sbio->bio = NULL;
    spin_lock(&sdev->list_lock);
    sbio->next_free = sdev->first_free;
    sdev->first_free = sbio->index;
    spin_unlock(&sdev->list_lock);
    atomic_dec(&sdev->in_flight);
    wake_up(&sdev->list_wait);
}

static void scrub_block_complete(struct scrub_block *sblock)
{
    if (!sblock->no_io_error_seen)
        scrub_handle_errored_block(sblock);
    else
        scrub_checksum(sblock);
}

static int scrub_find_csum(struct scrub_dev *sdev, u64 logical, u64 len,
               u8 *csum)
{
    struct btrfs_ordered_sum *sum = NULL;
    int ret = 0;
    unsigned long i;
    unsigned long num_sectors;

    while (!list_empty(&sdev->csum_list)) {
        sum = list_first_entry(&sdev->csum_list,
                       struct btrfs_ordered_sum, list);
        if (sum->bytenr > logical)
            return 0;
        if (sum->bytenr + sum->len > logical)
            break;

        ++sdev->stat.csum_discards;
        list_del(&sum->list);
        kfree(sum);
        sum = NULL;
    }
    if (!sum)
        return 0;

    num_sectors = sum->len / sdev->sectorsize;
    for (i = 0; i < num_sectors; ++i) {
        if (sum->sums[i].bytenr == logical) {
            memcpy(csum, &sum->sums[i].sum, sdev->csum_size);
            ret = 1;
            break;
        }
    }
    if (ret && i == num_sectors - 1) {
        list_del(&sum->list);
        kfree(sum);
    }
    return ret;
}

/* scrub extent tries to collect up to 64 kB for each bio */
static int scrub_extent(struct scrub_dev *sdev, u64 logical, u64 len,
            u64 physical, u64 flags, u64 gen, int mirror_num)
{
    int ret;
    u8 csum[BTRFS_CSUM_SIZE];
    u32 blocksize;

    if (flags & BTRFS_EXTENT_FLAG_DATA) {
        blocksize = sdev->sectorsize;
        spin_lock(&sdev->stat_lock);
        sdev->stat.data_extents_scrubbed++;
        sdev->stat.data_bytes_scrubbed += len;
        spin_unlock(&sdev->stat_lock);
    } else if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
        BUG_ON(sdev->nodesize != sdev->leafsize);
        blocksize = sdev->nodesize;
        spin_lock(&sdev->stat_lock);
        sdev->stat.tree_extents_scrubbed++;
        sdev->stat.tree_bytes_scrubbed += len;
        spin_unlock(&sdev->stat_lock);
    } else {
        blocksize = sdev->sectorsize;
        BUG_ON(1);
    }

    while (len) {
        u64 l = min_t(u64, len, blocksize);
        int have_csum = 0;

        if (flags & BTRFS_EXTENT_FLAG_DATA) {
            /* push csums to sbio */
            have_csum = scrub_find_csum(sdev, logical, l, csum);
            if (have_csum == 0)
                ++sdev->stat.no_csum;
        }
        ret = scrub_pages(sdev, logical, l, physical, flags, gen,
                  mirror_num, have_csum ? csum : NULL, 0);
        if (ret)
            return ret;
        len -= l;
        logical += l;
        physical += l;
    }
    return 0;
}

static noinline_for_stack int scrub_stripe(struct scrub_dev *sdev,
    struct map_lookup *map, int num, u64 base, u64 length)
{
    struct btrfs_path *path;
    struct btrfs_fs_info *fs_info = sdev->dev->dev_root->fs_info;
    struct btrfs_root *root = fs_info->extent_root;
    struct btrfs_root *csum_root = fs_info->csum_root;
    struct btrfs_extent_item *extent;
    struct blk_plug plug;
    u64 flags;
    int ret;
    int slot;
    int i;
    u64 nstripes;
    struct extent_buffer *l;
    struct btrfs_key key;
    u64 physical;
    u64 logical;
    u64 generation;
    int mirror_num;
    struct reada_control *reada1;
    struct reada_control *reada2;
    struct btrfs_key key_start;
    struct btrfs_key key_end;

    u64 increment = map->stripe_len;
    u64 offset;

    nstripes = length;
    offset = 0;
    do_div(nstripes, map->stripe_len);
    if (map->type & BTRFS_BLOCK_GROUP_RAID0) {
        offset = map->stripe_len * num;
        increment = map->stripe_len * map->num_stripes;
        mirror_num = 1;
    } else if (map->type & BTRFS_BLOCK_GROUP_RAID10) {
        int factor = map->num_stripes / map->sub_stripes;
        offset = map->stripe_len * (num / map->sub_stripes);
        increment = map->stripe_len * factor;
        mirror_num = num % map->sub_stripes + 1;
    } else if (map->type & BTRFS_BLOCK_GROUP_RAID1) {
        increment = map->stripe_len;
        mirror_num = num % map->num_stripes + 1;
    } else if (map->type & BTRFS_BLOCK_GROUP_DUP) {
        increment = map->stripe_len;
        mirror_num = num % map->num_stripes + 1;
    } else {
        increment = map->stripe_len;
        mirror_num = 1;
    }

    path = btrfs_alloc_path();
    if (!path)
        return -ENOMEM;

    /*
     * work on commit root. The related disk blocks are static as
     * long as COW is applied. This means, it is save to rewrite
     * them to repair disk errors without any race conditions
     */
    path->search_commit_root = 1;
    path->skip_locking = 1;

    /*
     * trigger the readahead for extent tree csum tree and wait for
     * completion. During readahead, the scrub is officially paused
     * to not hold off transaction commits
     */
    logical = base + offset;

    wait_event(sdev->list_wait,
           atomic_read(&sdev->in_flight) == 0);
    atomic_inc(&fs_info->scrubs_paused);
    wake_up(&fs_info->scrub_pause_wait);

    /* FIXME it might be better to start readahead at commit root */
    key_start.objectid = logical;
    key_start.type = BTRFS_EXTENT_ITEM_KEY;
    key_start.offset = (u64)0;
    key_end.objectid = base + offset + nstripes * increment;
    key_end.type = BTRFS_EXTENT_ITEM_KEY;
    key_end.offset = (u64)0;
    reada1 = btrfs_reada_add(root, &key_start, &key_end);

    key_start.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
    key_start.type = BTRFS_EXTENT_CSUM_KEY;
    key_start.offset = logical;
    key_end.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
    key_end.type = BTRFS_EXTENT_CSUM_KEY;
    key_end.offset = base + offset + nstripes * increment;
    reada2 = btrfs_reada_add(csum_root, &key_start, &key_end);

    if (!IS_ERR(reada1))
        btrfs_reada_wait(reada1);
    if (!IS_ERR(reada2))
        btrfs_reada_wait(reada2);

    mutex_lock(&fs_info->scrub_lock);
    while (atomic_read(&fs_info->scrub_pause_req)) {
        mutex_unlock(&fs_info->scrub_lock);
        wait_event(fs_info->scrub_pause_wait,
           atomic_read(&fs_info->scrub_pause_req) == 0);
        mutex_lock(&fs_info->scrub_lock);
    }
    atomic_dec(&fs_info->scrubs_paused);
    mutex_unlock(&fs_info->scrub_lock);
    wake_up(&fs_info->scrub_pause_wait);

    /*
     * collect all data csums for the stripe to avoid seeking during
     * the scrub. This might currently (crc32) end up to be about 1MB
     */
    blk_start_plug(&plug);

    /*
     * now find all extents for each stripe and scrub them
     */
    logical = base + offset;
    physical = map->stripes[num].physical;
    ret = 0;
    for (i = 0; i < nstripes; ++i) {
        /*
         * canceled?
         */
        if (atomic_read(&fs_info->scrub_cancel_req) ||
            atomic_read(&sdev->cancel_req)) {
            ret = -ECANCELED;
            goto out;
        }
        /*
         * check to see if we have to pause
         */
        if (atomic_read(&fs_info->scrub_pause_req)) {
            /* push queued extents */
            scrub_submit(sdev);
            wait_event(sdev->list_wait,
                   atomic_read(&sdev->in_flight) == 0);
            atomic_inc(&fs_info->scrubs_paused);
            wake_up(&fs_info->scrub_pause_wait);
            mutex_lock(&fs_info->scrub_lock);
            while (atomic_read(&fs_info->scrub_pause_req)) {
                mutex_unlock(&fs_info->scrub_lock);
                wait_event(fs_info->scrub_pause_wait,
                   atomic_read(&fs_info->scrub_pause_req) == 0);
                mutex_lock(&fs_info->scrub_lock);
            }
            atomic_dec(&fs_info->scrubs_paused);
            mutex_unlock(&fs_info->scrub_lock);
            wake_up(&fs_info->scrub_pause_wait);
        }

        ret = btrfs_lookup_csums_range(csum_root, logical,
                           logical + map->stripe_len - 1,
                           &sdev->csum_list, 1);
        if (ret)
            goto out;

        key.objectid = logical;
        key.type = BTRFS_EXTENT_ITEM_KEY;
        key.offset = (u64)0;

        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
            goto out;
        if (ret > 0) {
            ret = btrfs_previous_item(root, path, 0,
                          BTRFS_EXTENT_ITEM_KEY);
            if (ret < 0)
                goto out;
            if (ret > 0) {
                /* there's no smaller item, so stick with the
                 * larger one */
                btrfs_release_path(path);
                ret = btrfs_search_slot(NULL, root, &key,
                            path, 0, 0);
                if (ret < 0)
                    goto out;
            }
        }

        while (1) {
            l = path->nodes[0];
            slot = path->slots[0];
            if (slot >= btrfs_header_nritems(l)) {
                ret = btrfs_next_leaf(root, path);
                if (ret == 0)
                    continue;
                if (ret < 0)
                    goto out;

                break;
            }
            btrfs_item_key_to_cpu(l, &key, slot);

            if (key.objectid + key.offset <= logical)
                goto next;

            if (key.objectid >= logical + map->stripe_len)
                break;

            if (btrfs_key_type(&key) != BTRFS_EXTENT_ITEM_KEY)
                goto next;

            extent = btrfs_item_ptr(l, slot,
                        struct btrfs_extent_item);
            flags = btrfs_extent_flags(l, extent);
            generation = btrfs_extent_generation(l, extent);

            if (key.objectid < logical &&
                (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)) {
                printk(KERN_ERR
                       "btrfs scrub: tree block %llu spanning "
                       "stripes, ignored. logical=%llu\n",
                       (unsigned long long)key.objectid,
                       (unsigned long long)logical);
                goto next;
            }

            /*
             * trim extent to this stripe
             */
            if (key.objectid < logical) {
                key.offset -= logical - key.objectid;
                key.objectid = logical;
            }
            if (key.objectid + key.offset >
                logical + map->stripe_len) {
                key.offset = logical + map->stripe_len -
                         key.objectid;
            }

            ret = scrub_extent(sdev, key.objectid, key.offset,
                       key.objectid - logical + physical,
                       flags, generation, mirror_num);
            if (ret)
                goto out;

next:
            path->slots[0]++;
        }
        btrfs_release_path(path);
        logical += increment;
        physical += map->stripe_len;
        spin_lock(&sdev->stat_lock);
        sdev->stat.last_physical = physical;
        spin_unlock(&sdev->stat_lock);
    }
    /* push queued extents */
    scrub_submit(sdev);

out:
    blk_finish_plug(&plug);
    btrfs_free_path(path);
    return ret < 0 ? ret : 0;
}

static noinline_for_stack int scrub_chunk(struct scrub_dev *sdev,
    u64 chunk_tree, u64 chunk_objectid, u64 chunk_offset, u64 length,
    u64 dev_offset)
{
    struct btrfs_mapping_tree *map_tree =
        &sdev->dev->dev_root->fs_info->mapping_tree;
    struct map_lookup *map;
    struct extent_map *em;
    int i;
    int ret = -EINVAL;

    read_lock(&map_tree->map_tree.lock);
    em = lookup_extent_mapping(&map_tree->map_tree, chunk_offset, 1);
    read_unlock(&map_tree->map_tree.lock);

    if (!em)
        return -EINVAL;

    map = (struct map_lookup *)em->bdev;
    if (em->start != chunk_offset)
        goto out;

    if (em->len < length)
        goto out;

    for (i = 0; i < map->num_stripes; ++i) {
        if (map->stripes[i].dev == sdev->dev &&
            map->stripes[i].physical == dev_offset) {
            ret = scrub_stripe(sdev, map, i, chunk_offset, length);
            if (ret)
                goto out;
        }
    }
out:
    free_extent_map(em);

    return ret;
}

static noinline_for_stack
int scrub_enumerate_chunks(struct scrub_dev *sdev, u64 start, u64 end)
{
    struct btrfs_dev_extent *dev_extent = NULL;
    struct btrfs_path *path;
    struct btrfs_root *root = sdev->dev->dev_root;
    struct btrfs_fs_info *fs_info = root->fs_info;
    u64 length;
    u64 chunk_tree;
    u64 chunk_objectid;
    u64 chunk_offset;
    int ret;
    int slot;
    struct extent_buffer *l;
    struct btrfs_key key;
    struct btrfs_key found_key;
    struct btrfs_block_group_cache *cache;

    path = btrfs_alloc_path();
    if (!path)
        return -ENOMEM;

    path->reada = 2;
    path->search_commit_root = 1;
    path->skip_locking = 1;

    key.objectid = sdev->dev->devid;
    key.offset = 0ull;
    key.type = BTRFS_DEV_EXTENT_KEY;


    while (1) {
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
            break;
        if (ret > 0) {
            if (path->slots[0] >=
                btrfs_header_nritems(path->nodes[0])) {
                ret = btrfs_next_leaf(root, path);
                if (ret)
                    break;
            }
        }

        l = path->nodes[0];
        slot = path->slots[0];

        btrfs_item_key_to_cpu(l, &found_key, slot);

        if (found_key.objectid != sdev->dev->devid)
            break;

        if (btrfs_key_type(&found_key) != BTRFS_DEV_EXTENT_KEY)
            break;

        if (found_key.offset >= end)
            break;

        if (found_key.offset < key.offset)
            break;

        dev_extent = btrfs_item_ptr(l, slot, struct btrfs_dev_extent);
        length = btrfs_dev_extent_length(l, dev_extent);

        if (found_key.offset + length <= start) {
            key.offset = found_key.offset + length;
            btrfs_release_path(path);
            continue;
        }

        chunk_tree = btrfs_dev_extent_chunk_tree(l, dev_extent);
        chunk_objectid = btrfs_dev_extent_chunk_objectid(l, dev_extent);
        chunk_offset = btrfs_dev_extent_chunk_offset(l, dev_extent);

        /*
         * get a reference on the corresponding block group to prevent
         * the chunk from going away while we scrub it
         */
        cache = btrfs_lookup_block_group(fs_info, chunk_offset);
        if (!cache) {
            ret = -ENOENT;
            break;
        }
        ret = scrub_chunk(sdev, chunk_tree, chunk_objectid,
                  chunk_offset, length, found_key.offset);
        btrfs_put_block_group(cache);
        if (ret)
            break;

        key.offset = found_key.offset + length;
        btrfs_release_path(path);
    }

    btrfs_free_path(path);

    /*
     * ret can still be 1 from search_slot or next_leaf,
     * that's not an error
     */
    return ret < 0 ? ret : 0;
}

static noinline_for_stack int scrub_supers(struct scrub_dev *sdev)
{
    int i;
    u64 bytenr;
    u64 gen;
    int ret;
    struct btrfs_device *device = sdev->dev;
    struct btrfs_root *root = device->dev_root;

    if (root->fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR)
        return -EIO;

    gen = root->fs_info->last_trans_committed;

    for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
        bytenr = btrfs_sb_offset(i);
        if (bytenr + BTRFS_SUPER_INFO_SIZE > device->total_bytes)
            break;

        ret = scrub_pages(sdev, bytenr, BTRFS_SUPER_INFO_SIZE, bytenr,
                     BTRFS_EXTENT_FLAG_SUPER, gen, i, NULL, 1);
        if (ret)
            return ret;
    }
    wait_event(sdev->list_wait, atomic_read(&sdev->in_flight) == 0);

    return 0;
}

/*
 * get a reference count on fs_info->scrub_workers. start worker if necessary
 */
static noinline_for_stack int scrub_workers_get(struct btrfs_root *root)
{
    struct btrfs_fs_info *fs_info = root->fs_info;
    int ret = 0;

    mutex_lock(&fs_info->scrub_lock);
    if (fs_info->scrub_workers_refcnt == 0) {
        btrfs_init_workers(&fs_info->scrub_workers, "scrub",
               fs_info->thread_pool_size, &fs_info->generic_worker);
        fs_info->scrub_workers.idle_thresh = 4;
        ret = btrfs_start_workers(&fs_info->scrub_workers);
        if (ret)
            goto out;
    }
    ++fs_info->scrub_workers_refcnt;
out:
    mutex_unlock(&fs_info->scrub_lock);

    return ret;
}

static noinline_for_stack void scrub_workers_put(struct btrfs_root *root)
{
    struct btrfs_fs_info *fs_info = root->fs_info;

    mutex_lock(&fs_info->scrub_lock);
    if (--fs_info->scrub_workers_refcnt == 0)
        btrfs_stop_workers(&fs_info->scrub_workers);
    WARN_ON(fs_info->scrub_workers_refcnt < 0);
    mutex_unlock(&fs_info->scrub_lock);
}


int btrfs_scrub_dev(struct btrfs_root *root, u64 devid, u64 start, u64 end,
            struct btrfs_scrub_progress *progress, int readonly)
{
    struct scrub_dev *sdev;
    struct btrfs_fs_info *fs_info = root->fs_info;
    int ret;
    struct btrfs_device *dev;

    if (btrfs_fs_closing(root->fs_info))
        return -EINVAL;

    /*
     * check some assumptions
     */
    if (root->nodesize != root->leafsize) {
        printk(KERN_ERR
               "btrfs_scrub: size assumption nodesize == leafsize (%d == %d) fails\n",
               root->nodesize, root->leafsize);
        return -EINVAL;
    }

    if (root->nodesize > BTRFS_STRIPE_LEN) {
        /*
         * in this case scrub is unable to calculate the checksum
         * the way scrub is implemented. Do not handle this
         * situation at all because it won't ever happen.
         */
        printk(KERN_ERR
               "btrfs_scrub: size assumption nodesize <= BTRFS_STRIPE_LEN (%d <= %d) fails\n",
               root->nodesize, BTRFS_STRIPE_LEN);
        return -EINVAL;
    }

    if (root->sectorsize != PAGE_SIZE) {
        /* not supported for data w/o checksums */
        printk(KERN_ERR
               "btrfs_scrub: size assumption sectorsize != PAGE_SIZE (%d != %lld) fails\n",
               root->sectorsize, (unsigned long long)PAGE_SIZE);
        return -EINVAL;
    }

    ret = scrub_workers_get(root);
    if (ret)
        return ret;

    mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
    dev = btrfs_find_device(root, devid, NULL, NULL);
    if (!dev || dev->missing) {
        mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
        scrub_workers_put(root);
        return -ENODEV;
    }
    mutex_lock(&fs_info->scrub_lock);

    if (!dev->in_fs_metadata) {
        mutex_unlock(&fs_info->scrub_lock);
        mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
        scrub_workers_put(root);
        return -ENODEV;
    }

    if (dev->scrub_device) {
        mutex_unlock(&fs_info->scrub_lock);
        mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
        scrub_workers_put(root);
        return -EINPROGRESS;
    }
    sdev = scrub_setup_dev(dev);
    if (IS_ERR(sdev)) {
        mutex_unlock(&fs_info->scrub_lock);
        mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
        scrub_workers_put(root);
        return PTR_ERR(sdev);
    }
    sdev->readonly = readonly;
    dev->scrub_device = sdev;

    atomic_inc(&fs_info->scrubs_running);
    mutex_unlock(&fs_info->scrub_lock);
    mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);

    down_read(&fs_info->scrub_super_lock);
    ret = scrub_supers(sdev);
    up_read(&fs_info->scrub_super_lock);

    if (!ret)
        ret = scrub_enumerate_chunks(sdev, start, end);

    wait_event(sdev->list_wait, atomic_read(&sdev->in_flight) == 0);
    atomic_dec(&fs_info->scrubs_running);
    wake_up(&fs_info->scrub_pause_wait);

    wait_event(sdev->list_wait, atomic_read(&sdev->fixup_cnt) == 0);

    if (progress)
        memcpy(progress, &sdev->stat, sizeof(*progress));

    mutex_lock(&fs_info->scrub_lock);
    dev->scrub_device = NULL;
    mutex_unlock(&fs_info->scrub_lock);

    scrub_free_dev(sdev);
    scrub_workers_put(root);

    return ret;
}

void btrfs_scrub_pause(struct btrfs_root *root)
{
    struct btrfs_fs_info *fs_info = root->fs_info;

    mutex_lock(&fs_info->scrub_lock);
    atomic_inc(&fs_info->scrub_pause_req);
    while (atomic_read(&fs_info->scrubs_paused) !=
           atomic_read(&fs_info->scrubs_running)) {
        mutex_unlock(&fs_info->scrub_lock);
        wait_event(fs_info->scrub_pause_wait,
               atomic_read(&fs_info->scrubs_paused) ==
               atomic_read(&fs_info->scrubs_running));
        mutex_lock(&fs_info->scrub_lock);
    }
    mutex_unlock(&fs_info->scrub_lock);
}

void btrfs_scrub_continue(struct btrfs_root *root)
{
    struct btrfs_fs_info *fs_info = root->fs_info;

    atomic_dec(&fs_info->scrub_pause_req);
    wake_up(&fs_info->scrub_pause_wait);
}

void btrfs_scrub_pause_super(struct btrfs_root *root)
{
    down_write(&root->fs_info->scrub_super_lock);
}

void btrfs_scrub_continue_super(struct btrfs_root *root)
{
    up_write(&root->fs_info->scrub_super_lock);
}

int __btrfs_scrub_cancel(struct btrfs_fs_info *fs_info)
{

    mutex_lock(&fs_info->scrub_lock);
    if (!atomic_read(&fs_info->scrubs_running)) {
        mutex_unlock(&fs_info->scrub_lock);
        return -ENOTCONN;
    }

    atomic_inc(&fs_info->scrub_cancel_req);
    while (atomic_read(&fs_info->scrubs_running)) {
        mutex_unlock(&fs_info->scrub_lock);
        wait_event(fs_info->scrub_pause_wait,
               atomic_read(&fs_info->scrubs_running) == 0);
        mutex_lock(&fs_info->scrub_lock);
    }
    atomic_dec(&fs_info->scrub_cancel_req);
    mutex_unlock(&fs_info->scrub_lock);

    return 0;
}

int btrfs_scrub_cancel(struct btrfs_root *root)
{
    return __btrfs_scrub_cancel(root->fs_info);
}

int btrfs_scrub_cancel_dev(struct btrfs_root *root, struct btrfs_device *dev)
{
    struct btrfs_fs_info *fs_info = root->fs_info;
    struct scrub_dev *sdev;

    mutex_lock(&fs_info->scrub_lock);
    sdev = dev->scrub_device;
    if (!sdev) {
        mutex_unlock(&fs_info->scrub_lock);
        return -ENOTCONN;
    }
    atomic_inc(&sdev->cancel_req);
    while (dev->scrub_device) {
        mutex_unlock(&fs_info->scrub_lock);
        wait_event(fs_info->scrub_pause_wait,
               dev->scrub_device == NULL);
        mutex_lock(&fs_info->scrub_lock);
    }
    mutex_unlock(&fs_info->scrub_lock);

    return 0;
}

int btrfs_scrub_cancel_devid(struct btrfs_root *root, u64 devid)
{
    struct btrfs_fs_info *fs_info = root->fs_info;
    struct btrfs_device *dev;
    int ret;

    /*
     * we have to hold the device_list_mutex here so the device
     * does not go away in cancel_dev. FIXME: find a better solution
     */
    mutex_lock(&fs_info->fs_devices->device_list_mutex);
    dev = btrfs_find_device(root, devid, NULL, NULL);
    if (!dev) {
        mutex_unlock(&fs_info->fs_devices->device_list_mutex);
        return -ENODEV;
    }
    ret = btrfs_scrub_cancel_dev(root, dev);
    mutex_unlock(&fs_info->fs_devices->device_list_mutex);

    return ret;
}

int btrfs_scrub_progress(struct btrfs_root *root, u64 devid,
             struct btrfs_scrub_progress *progress)
{
    struct btrfs_device *dev;
    struct scrub_dev *sdev = NULL;

    mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
    dev = btrfs_find_device(root, devid, NULL, NULL);
    if (dev)
        sdev = dev->scrub_device;
    if (sdev)
        memcpy(progress, &sdev->stat, sizeof(*progress));
    mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);

    return dev ? (sdev ? 0 : -ENOTCONN) : -ENODEV;
}