1 files changed, 519 insertions, 141 deletions

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index a8d03d5efb5d..c27bcb67f330 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -17,10 +17,14 @@
  */
 
 #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"
 
 /*
  * This is only the first step towards a full-features scrub. It reads all
@@ -29,15 +33,12 @@
  * any can be found.
  *
  * Future enhancements:
- *  - To enhance the performance, better read-ahead strategies for the
- *    extent-tree can be employed.
  *  - In case an unrepairable extent is encountered, track which files are
  *    affected and report them
  *  - In case of a read error on files with nodatasum, map the file and read
  *    the extent to trigger a writeback of the good copy
  *  - track and record media errors, throw out bad devices
  *  - add a mode to also read unallocated space
- *  - make the prefetch cancellable
  */
 
 struct scrub_bio;
@@ -63,7 +64,7 @@ static void scrub_fixup(struct scrub_bio *sbio, int ix);
 struct scrub_page {
         u64                     flags;  /* extent flags */
         u64                     generation;
-        u64                     mirror_num;
+        int                     mirror_num;
         int                     have_csum;
         u8                      csum[BTRFS_CSUM_SIZE];
 };
@@ -87,6 +88,7 @@ struct scrub_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;
@@ -100,6 +102,27 @@ struct scrub_dev {
         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 void scrub_free_csums(struct scrub_dev *sdev)
 {
         while (!list_empty(&sdev->csum_list)) {
@@ -175,14 +198,15 @@ struct scrub_dev *scrub_setup_dev(struct btrfs_device *dev)
 
                 if (i != SCRUB_BIOS_PER_DEV-1)
                         sdev->bios[i]->next_free = i + 1;
-                 else
+                else
                         sdev->bios[i]->next_free = -1;
         }
         sdev->first_free = 0;
         sdev->curr = -1;
         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);
+        sdev->csum_size = btrfs_super_csum_size(fs_info->super_copy);
         INIT_LIST_HEAD(&sdev->csum_list);
 
         spin_lock_init(&sdev->list_lock);
@@ -195,24 +219,366 @@ nomem:
         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(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, 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(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, 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_bio *sbio,
+                                int ix)
+{
+        struct btrfs_device *dev = sbio->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;
+        u32 item_size;
+        int ret;
+        u64 ref_root;
+        u8 ref_level;
+        unsigned long ptr = 0;
+        const int bufsize = 4096;
+        u64 extent_offset;
+
+        path = btrfs_alloc_path();
+
+        swarn.scratch_buf = kmalloc(bufsize, GFP_NOFS);
+        swarn.msg_buf = kmalloc(bufsize, GFP_NOFS);
+        swarn.sector = (sbio->physical + ix * PAGE_SIZE) >> 9;
+        swarn.logical = sbio->logical + ix * PAGE_SIZE;
+        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);
+        if (ret < 0)
+                goto out;
+
+        extent_offset = 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]);
+
+        if (ret & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
+                do {
+                        ret = tree_backref_for_extent(&ptr, eb, ei, item_size,
+                                                        &ref_root, &ref_level);
+                        printk(KERN_WARNING "%s at logical %llu on dev %s, "
+                                "sector %llu: metadata %s (level %d) in tree "
+                                "%llu\n", errstr, swarn.logical, 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, path, found_key.objectid,
+                                        extent_offset,
+                                        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(KERN_ERR "btrfs: unable to fixup "
+                                        "(nodatasum) error at logical %llu\n",
+                                        fixup->logical);
+        }
+
+        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_recheck_error gets called when either verification of the page
  * failed or the bio failed to read, e.g. with EIO. In the latter case,
  * recheck_error gets called for every page in the bio, even though only
  * one may be bad
  */
-static void scrub_recheck_error(struct scrub_bio *sbio, int ix)
+static int scrub_recheck_error(struct scrub_bio *sbio, int ix)
 {
+        struct scrub_dev *sdev = sbio->sdev;
+        u64 sector = (sbio->physical + ix * PAGE_SIZE) >> 9;
+        static DEFINE_RATELIMIT_STATE(_rs, DEFAULT_RATELIMIT_INTERVAL,
+                                        DEFAULT_RATELIMIT_BURST);
+
         if (sbio->err) {
-                if (scrub_fixup_io(READ, sbio->sdev->dev->bdev,
-                                   (sbio->physical + ix * PAGE_SIZE) >> 9,
+                if (scrub_fixup_io(READ, sbio->sdev->dev->bdev, sector,
                                    sbio->bio->bi_io_vec[ix].bv_page) == 0) {
                         if (scrub_fixup_check(sbio, ix) == 0)
-                                return;
+                                return 0;
                 }
+                if (__ratelimit(&_rs))
+                        scrub_print_warning("i/o error", sbio, ix);
+        } else {
+                if (__ratelimit(&_rs))
+                        scrub_print_warning("checksum error", sbio, ix);
         }
 
+        spin_lock(&sdev->stat_lock);
+        ++sdev->stat.read_errors;
+        spin_unlock(&sdev->stat_lock);
+
         scrub_fixup(sbio, ix);
+        return 1;
 }
 
 static int scrub_fixup_check(struct scrub_bio *sbio, int ix)
@@ -250,7 +616,8 @@ static void scrub_fixup(struct scrub_bio *sbio, int ix)
         struct scrub_dev *sdev = sbio->sdev;
         struct btrfs_fs_info *fs_info = sdev->dev->dev_root->fs_info;
         struct btrfs_mapping_tree *map_tree = &fs_info->mapping_tree;
-        struct btrfs_multi_bio *multi = NULL;
+        struct btrfs_bio *bbio = NULL;
+        struct scrub_fixup_nodatasum *fixup;
         u64 logical = sbio->logical + ix * PAGE_SIZE;
         u64 length;
         int i;
@@ -259,38 +626,57 @@ static void scrub_fixup(struct scrub_bio *sbio, int ix)
 
         if ((sbio->spag[ix].flags & BTRFS_EXTENT_FLAG_DATA) &&
             (sbio->spag[ix].have_csum == 0)) {
+                fixup = kzalloc(sizeof(*fixup), GFP_NOFS);
+                if (!fixup)
+                        goto uncorrectable;
+                fixup->sdev = sdev;
+                fixup->logical = logical;
+                fixup->root = fs_info->extent_root;
+                fixup->mirror_num = sbio->spag[ix].mirror_num;
                 /*
-                 * nodatasum, don't try to fix anything
-                 * FIXME: we can do better, open the inode and trigger a
-                 * writeback
+                 * 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.
                  */
-                goto uncorrectable;
+                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->work.func = scrub_fixup_nodatasum;
+                btrfs_queue_worker(&fs_info->scrub_workers, &fixup->work);
+                return;
         }
 
         length = PAGE_SIZE;
         ret = btrfs_map_block(map_tree, REQ_WRITE, logical, &length,
-                              &multi, 0);
-        if (ret || !multi || length < PAGE_SIZE) {
+                              &bbio, 0);
+        if (ret || !bbio || length < PAGE_SIZE) {
                 printk(KERN_ERR
                        "scrub_fixup: btrfs_map_block failed us for %llu\n",
                        (unsigned long long)logical);
                 WARN_ON(1);
+                kfree(bbio);
                 return;
         }
 
-        if (multi->num_stripes == 1)
+        if (bbio->num_stripes == 1)
                 /* there aren't any replicas */
                 goto uncorrectable;
 
         /*
          * first find a good copy
          */
-        for (i = 0; i < multi->num_stripes; ++i) {
-                if (i == sbio->spag[ix].mirror_num)
+        for (i = 0; i < bbio->num_stripes; ++i) {
+                if (i + 1 == sbio->spag[ix].mirror_num)
                         continue;
 
-                if (scrub_fixup_io(READ, multi->stripes[i].dev->bdev,
-                                   multi->stripes[i].physical >> 9,
+                if (scrub_fixup_io(READ, bbio->stripes[i].dev->bdev,
+                                   bbio->stripes[i].physical >> 9,
                                    sbio->bio->bi_io_vec[ix].bv_page)) {
                         /* I/O-error, this is not a good copy */
                         continue;
@@ -299,7 +685,7 @@ static void scrub_fixup(struct scrub_bio *sbio, int ix)
                 if (scrub_fixup_check(sbio, ix) == 0)
                         break;
         }
-        if (i == multi->num_stripes)
+        if (i == bbio->num_stripes)
                 goto uncorrectable;
 
         if (!sdev->readonly) {
@@ -314,25 +700,23 @@ static void scrub_fixup(struct scrub_bio *sbio, int ix)
                 }
         }
 
-        kfree(multi);
+        kfree(bbio);
         spin_lock(&sdev->stat_lock);
         ++sdev->stat.corrected_errors;
         spin_unlock(&sdev->stat_lock);
 
-        if (printk_ratelimit())
-                printk(KERN_ERR "btrfs: fixed up at %llu\n",
-                       (unsigned long long)logical);
+        printk_ratelimited(KERN_ERR "btrfs: fixed up error at logical %llu\n",
+                               (unsigned long long)logical);
         return;
 
 uncorrectable:
-        kfree(multi);
+        kfree(bbio);
         spin_lock(&sdev->stat_lock);
         ++sdev->stat.uncorrectable_errors;
         spin_unlock(&sdev->stat_lock);
 
-        if (printk_ratelimit())
-                printk(KERN_ERR "btrfs: unable to fixup at %llu\n",
-                         (unsigned long long)logical);
+        printk_ratelimited(KERN_ERR "btrfs: unable to fixup (regular) error at "
+                                "logical %llu\n", (unsigned long long)logical);
 }
 
 static int scrub_fixup_io(int rw, struct block_device *bdev, sector_t sector,
@@ -382,8 +766,14 @@ static void scrub_checksum(struct btrfs_work *work)
         int ret;
 
         if (sbio->err) {
+                ret = 0;
                 for (i = 0; i < sbio->count; ++i)
-                        scrub_recheck_error(sbio, i);
+                        ret |= scrub_recheck_error(sbio, i);
+                if (!ret) {
+                        spin_lock(&sdev->stat_lock);
+                        ++sdev->stat.unverified_errors;
+                        spin_unlock(&sdev->stat_lock);
+                }
 
                 sbio->bio->bi_flags &= ~(BIO_POOL_MASK - 1);
                 sbio->bio->bi_flags |= 1 << BIO_UPTODATE;
@@ -396,10 +786,6 @@ static void scrub_checksum(struct btrfs_work *work)
                         bi->bv_offset = 0;
                         bi->bv_len = PAGE_SIZE;
                 }
-
-                spin_lock(&sdev->stat_lock);
-                ++sdev->stat.read_errors;
-                spin_unlock(&sdev->stat_lock);
                 goto out;
         }
         for (i = 0; i < sbio->count; ++i) {
@@ -420,8 +806,14 @@ static void scrub_checksum(struct btrfs_work *work)
                         WARN_ON(1);
                 }
                 kunmap_atomic(buffer, KM_USER0);
-                if (ret)
-                        scrub_recheck_error(sbio, i);
+                if (ret) {
+                        ret = scrub_recheck_error(sbio, i);
+                        if (!ret) {
+                                spin_lock(&sdev->stat_lock);
+                                ++sdev->stat.unverified_errors;
+                                spin_unlock(&sdev->stat_lock);
+                        }
+                }
         }
 
 out:
@@ -557,57 +949,27 @@ static int scrub_checksum_super(struct scrub_bio *sbio, void *buffer)
 static int scrub_submit(struct scrub_dev *sdev)
 {
         struct scrub_bio *sbio;
-        struct bio *bio;
-        int i;
 
         if (sdev->curr == -1)
                 return 0;
 
         sbio = sdev->bios[sdev->curr];
-
-        bio = bio_alloc(GFP_NOFS, sbio->count);
-        if (!bio)
-                goto nomem;
-
-        bio->bi_private = sbio;
-        bio->bi_end_io = scrub_bio_end_io;
-        bio->bi_bdev = sdev->dev->bdev;
-        bio->bi_sector = sbio->physical >> 9;
-
-        for (i = 0; i < sbio->count; ++i) {
-                struct page *page;
-                int ret;
-
-                page = alloc_page(GFP_NOFS);
-                if (!page)
-                        goto nomem;
-
-                ret = bio_add_page(bio, page, PAGE_SIZE, 0);
-                if (!ret) {
-                        __free_page(page);
-                        goto nomem;
-                }
-        }
-
         sbio->err = 0;
         sdev->curr = -1;
         atomic_inc(&sdev->in_flight);
 
-        submit_bio(READ, bio);
+        submit_bio(READ, sbio->bio);
 
         return 0;
-
-nomem:
-        scrub_free_bio(bio);
-
-        return -ENOMEM;
 }
 
 static int scrub_page(struct scrub_dev *sdev, u64 logical, u64 len,
-                      u64 physical, u64 flags, u64 gen, u64 mirror_num,
+                      u64 physical, u64 flags, u64 gen, int mirror_num,
                       u8 *csum, int force)
 {
         struct scrub_bio *sbio;
+        struct page *page;
+        int ret;
 
 again:
         /*
@@ -628,12 +990,22 @@ again:
         }
         sbio = sdev->bios[sdev->curr];
         if (sbio->count == 0) {
+                struct bio *bio;
+
                 sbio->physical = physical;
                 sbio->logical = logical;
+                bio = bio_alloc(GFP_NOFS, SCRUB_PAGES_PER_BIO);
+                if (!bio)
+                        return -ENOMEM;
+
+                bio->bi_private = sbio;
+                bio->bi_end_io = scrub_bio_end_io;
+                bio->bi_bdev = sdev->dev->bdev;
+                bio->bi_sector = sbio->physical >> 9;
+                sbio->err = 0;
+                sbio->bio = bio;
         } else if (sbio->physical + sbio->count * PAGE_SIZE != physical ||
                    sbio->logical + sbio->count * PAGE_SIZE != logical) {
-                int ret;
-
                 ret = scrub_submit(sdev);
                 if (ret)
                         return ret;
@@ -643,6 +1015,20 @@ again:
         sbio->spag[sbio->count].generation = gen;
         sbio->spag[sbio->count].have_csum = 0;
         sbio->spag[sbio->count].mirror_num = mirror_num;
+
+        page = alloc_page(GFP_NOFS);
+        if (!page)
+                return -ENOMEM;
+
+        ret = bio_add_page(sbio->bio, page, PAGE_SIZE, 0);
+        if (!ret) {
+                __free_page(page);
+                ret = scrub_submit(sdev);
+                if (ret)
+                        return ret;
+                goto again;
+        }
+
         if (csum) {
                 sbio->spag[sbio->count].have_csum = 1;
                 memcpy(sbio->spag[sbio->count].csum, csum, sdev->csum_size);
@@ -701,7 +1087,7 @@ static int scrub_find_csum(struct scrub_dev *sdev, u64 logical, u64 len,
 
 /* 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, u64 mirror_num)
+                        u64 physical, u64 flags, u64 gen, int mirror_num)
 {
         int ret;
         u8 csum[BTRFS_CSUM_SIZE];
@@ -741,13 +1127,16 @@ static noinline_for_stack int scrub_stripe(struct scrub_dev *sdev,
         int slot;
         int i;
         u64 nstripes;
-        int start_stripe;
         struct extent_buffer *l;
         struct btrfs_key key;
         u64 physical;
         u64 logical;
         u64 generation;
-        u64 mirror_num;
+        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;
@@ -758,102 +1147,88 @@ static noinline_for_stack int scrub_stripe(struct scrub_dev *sdev,
         if (map->type & BTRFS_BLOCK_GROUP_RAID0) {
                 offset = map->stripe_len * num;
                 increment = map->stripe_len * map->num_stripes;
-                mirror_num = 0;
+                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;
+                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;
+                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;
+                mirror_num = num % map->num_stripes + 1;
         } else {
                 increment = map->stripe_len;
-                mirror_num = 0;
+                mirror_num = 1;
         }
 
         path = btrfs_alloc_path();
         if (!path)
                 return -ENOMEM;
 
-        path->reada = 2;
         path->search_commit_root = 1;
         path->skip_locking = 1;
 
         /*
-         * find all extents for each stripe and just read them to get
-         * them into the page cache
-         * FIXME: we can do better. build a more intelligent prefetching
+         * 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;
-        physical = map->stripes[num].physical;
-        ret = 0;
-        for (i = 0; i < nstripes; ++i) {
-                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_noplug;
-
-                /*
-                 * we might miss half an extent here, but that doesn't matter,
-                 * as it's only the prefetch
-                 */
-                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_noplug;
 
-                                break;
-                        }
-                        btrfs_item_key_to_cpu(l, &key, slot);
+        wait_event(sdev->list_wait,
+                   atomic_read(&sdev->in_flight) == 0);
+        atomic_inc(&fs_info->scrubs_paused);
+        wake_up(&fs_info->scrub_pause_wait);
 
-                        if (key.objectid >= logical + map->stripe_len)
-                                break;
+        /* 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);
 
-                        path->slots[0]++;
-                }
-                btrfs_release_path(path);
-                logical += increment;
-                physical += map->stripe_len;
-                cond_resched();
+        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
          */
-        start_stripe = 0;
         blk_start_plug(&plug);
-again:
-        logical = base + offset + start_stripe * increment;
-        for (i = start_stripe; i < nstripes; ++i) {
-                ret = btrfs_lookup_csums_range(csum_root, logical,
-                                               logical + map->stripe_len - 1,
-                                               &sdev->csum_list, 1);
-                if (ret)
-                        goto out;
 
-                logical += increment;
-                cond_resched();
-        }
         /*
          * now find all extents for each stripe and scrub them
          */
-        logical = base + offset + start_stripe * increment;
-        physical = map->stripes[num].physical + start_stripe * map->stripe_len;
+        logical = base + offset;
+        physical = map->stripes[num].physical;
         ret = 0;
-        for (i = start_stripe; i < nstripes; ++i) {
+        for (i = 0; i < nstripes; ++i) {
                 /*
                  * canceled?
                  */
@@ -882,11 +1257,14 @@ again:
                         atomic_dec(&fs_info->scrubs_paused);
                         mutex_unlock(&fs_info->scrub_lock);
                         wake_up(&fs_info->scrub_pause_wait);
-                        scrub_free_csums(sdev);
-                        start_stripe = i;
-                        goto again;
                 }
 
+                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;
@@ -982,7 +1360,6 @@ next:
 
 out:
         blk_finish_plug(&plug);
-out_noplug:
         btrfs_free_path(path);
         return ret < 0 ? ret : 0;
 }
@@ -1253,10 +1630,11 @@ int btrfs_scrub_dev(struct btrfs_root *root, u64 devid, u64 start, u64 end,
                 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));