1 files changed, 514 insertions, 84 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 993f93ff7ba6..d0c4d584efad 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -68,6 +68,8 @@ static int pin_down_bytes(struct btrfs_trans_handle *trans,
                           struct extent_buffer **must_clean);
 static int find_next_key(struct btrfs_path *path, int level,
                          struct btrfs_key *key);
+static void dump_space_info(struct btrfs_space_info *info, u64 bytes,
+                            int dump_block_groups);
 
 static noinline int
 block_group_cache_done(struct btrfs_block_group_cache *cache)
@@ -2765,67 +2767,448 @@ void btrfs_set_inode_space_info(struct btrfs_root *root, struct inode *inode)
                                                        alloc_target);
 }
 
+static u64 calculate_bytes_needed(struct btrfs_root *root, int num_items)
+{
+        u64 num_bytes;
+        int level;
+
+        level = BTRFS_MAX_LEVEL - 2;
+        /*
+         * NOTE: these calculations are absolutely the worst possible case.
+         * This assumes that _every_ item we insert will require a new leaf, and
+         * that the tree has grown to its maximum level size.
+         */
+
+        /*
+         * for every item we insert we could insert both an extent item and a
+         * extent ref item.  Then for ever item we insert, we will need to cow
+         * both the original leaf, plus the leaf to the left and right of it.
+         *
+         * Unless we are talking about the extent root, then we just want the
+         * number of items * 2, since we just need the extent item plus its ref.
+         */
+        if (root == root->fs_info->extent_root)
+                num_bytes = num_items * 2;
+        else
+                num_bytes = (num_items + (2 * num_items)) * 3;
+
+        /*
+         * num_bytes is total number of leaves we could need times the leaf
+         * size, and then for every leaf we could end up cow'ing 2 nodes per
+         * level, down to the leaf level.
+         */
+        num_bytes = (num_bytes * root->leafsize) +
+                (num_bytes * (level * 2)) * root->nodesize;
+
+        return num_bytes;
+}
+
 /*
- * for now this just makes sure we have at least 5% of our metadata space free
- * for use.
+ * Unreserve metadata space for delalloc.  If we have less reserved credits than
+ * we have extents, this function does nothing.
  */
-int btrfs_check_metadata_free_space(struct btrfs_root *root)
+int btrfs_unreserve_metadata_for_delalloc(struct btrfs_root *root,
+                                          struct inode *inode, int num_items)
 {
         struct btrfs_fs_info *info = root->fs_info;
         struct btrfs_space_info *meta_sinfo;
-        u64 alloc_target, thresh;
-        int committed = 0, ret;
+        u64 num_bytes;
+        u64 alloc_target;
+        bool bug = false;
 
         /* get the space info for where the metadata will live */
         alloc_target = btrfs_get_alloc_profile(root, 0);
         meta_sinfo = __find_space_info(info, alloc_target);
-        if (!meta_sinfo)
-                goto alloc;
 
-again:
+        num_bytes = calculate_bytes_needed(root->fs_info->extent_root,
+                                           num_items);
+
         spin_lock(&meta_sinfo->lock);
-        if (!meta_sinfo->full)
-                thresh = meta_sinfo->total_bytes * 80;
-        else
-                thresh = meta_sinfo->total_bytes * 95;
+        spin_lock(&BTRFS_I(inode)->accounting_lock);
+        if (BTRFS_I(inode)->reserved_extents <=
+            BTRFS_I(inode)->outstanding_extents) {
+                spin_unlock(&BTRFS_I(inode)->accounting_lock);
+                spin_unlock(&meta_sinfo->lock);
+                return 0;
+        }
+        spin_unlock(&BTRFS_I(inode)->accounting_lock);
+
+        BTRFS_I(inode)->reserved_extents--;
+        BUG_ON(BTRFS_I(inode)->reserved_extents < 0);
+
+        if (meta_sinfo->bytes_delalloc < num_bytes) {
+                bug = true;
+                meta_sinfo->bytes_delalloc = 0;
+        } else {
+                meta_sinfo->bytes_delalloc -= num_bytes;
+        }
+        spin_unlock(&meta_sinfo->lock);
+
+        BUG_ON(bug);
 
+        return 0;
+}
+
+static void check_force_delalloc(struct btrfs_space_info *meta_sinfo)
+{
+        u64 thresh;
+
+        thresh = meta_sinfo->bytes_used + meta_sinfo->bytes_reserved +
+                meta_sinfo->bytes_pinned + meta_sinfo->bytes_readonly +
+                meta_sinfo->bytes_super + meta_sinfo->bytes_root +
+                meta_sinfo->bytes_may_use;
+
+        thresh = meta_sinfo->total_bytes - thresh;
+        thresh *= 80;
         do_div(thresh, 100);
+        if (thresh <= meta_sinfo->bytes_delalloc)
+                meta_sinfo->force_delalloc = 1;
+        else
+                meta_sinfo->force_delalloc = 0;
+}
 
-        if (meta_sinfo->bytes_used + meta_sinfo->bytes_reserved +
-            meta_sinfo->bytes_pinned + meta_sinfo->bytes_readonly +
-            meta_sinfo->bytes_super > thresh) {
-                struct btrfs_trans_handle *trans;
-                if (!meta_sinfo->full) {
-                        meta_sinfo->force_alloc = 1;
+struct async_flush {
+        struct btrfs_root *root;
+        struct btrfs_space_info *info;
+        struct btrfs_work work;
+};
+
+static noinline void flush_delalloc_async(struct btrfs_work *work)
+{
+        struct async_flush *async;
+        struct btrfs_root *root;
+        struct btrfs_space_info *info;
+
+        async = container_of(work, struct async_flush, work);
+        root = async->root;
+        info = async->info;
+
+        btrfs_start_delalloc_inodes(root);
+        wake_up(&info->flush_wait);
+        btrfs_wait_ordered_extents(root, 0);
+
+        spin_lock(&info->lock);
+        info->flushing = 0;
+        spin_unlock(&info->lock);
+        wake_up(&info->flush_wait);
+
+        kfree(async);
+}
+
+static void wait_on_flush(struct btrfs_space_info *info)
+{
+        DEFINE_WAIT(wait);
+        u64 used;
+
+        while (1) {
+                prepare_to_wait(&info->flush_wait, &wait,
+                                TASK_UNINTERRUPTIBLE);
+                spin_lock(&info->lock);
+                if (!info->flushing) {
+                        spin_unlock(&info->lock);
+                        break;
+                }
+
+                used = info->bytes_used + info->bytes_reserved +
+                        info->bytes_pinned + info->bytes_readonly +
+                        info->bytes_super + info->bytes_root +
+                        info->bytes_may_use + info->bytes_delalloc;
+                if (used < info->total_bytes) {
+                        spin_unlock(&info->lock);
+                        break;
+                }
+                spin_unlock(&info->lock);
+                schedule();
+        }
+        finish_wait(&info->flush_wait, &wait);
+}
+
+static void flush_delalloc(struct btrfs_root *root,
+                                 struct btrfs_space_info *info)
+{
+        struct async_flush *async;
+        bool wait = false;
+
+        spin_lock(&info->lock);
+
+        if (!info->flushing) {
+                info->flushing = 1;
+                init_waitqueue_head(&info->flush_wait);
+        } else {
+                wait = true;
+        }
+
+        spin_unlock(&info->lock);
+
+        if (wait) {
+                wait_on_flush(info);
+                return;
+        }
+
+        async = kzalloc(sizeof(*async), GFP_NOFS);
+        if (!async)
+                goto flush;
+
+        async->root = root;
+        async->info = info;
+        async->work.func = flush_delalloc_async;
+
+        btrfs_queue_worker(&root->fs_info->enospc_workers,
+                           &async->work);
+        wait_on_flush(info);
+        return;
+
+flush:
+        btrfs_start_delalloc_inodes(root);
+        btrfs_wait_ordered_extents(root, 0);
+
+        spin_lock(&info->lock);
+        info->flushing = 0;
+        spin_unlock(&info->lock);
+        wake_up(&info->flush_wait);
+}
+
+static int maybe_allocate_chunk(struct btrfs_root *root,
+                                 struct btrfs_space_info *info)
+{
+        struct btrfs_super_block *disk_super = &root->fs_info->super_copy;
+        struct btrfs_trans_handle *trans;
+        bool wait = false;
+        int ret = 0;
+        u64 min_metadata;
+        u64 free_space;
+
+        free_space = btrfs_super_total_bytes(disk_super);
+        /*
+         * we allow the metadata to grow to a max of either 5gb or 5% of the
+         * space in the volume.
+         */
+        min_metadata = min((u64)5 * 1024 * 1024 * 1024,
+                             div64_u64(free_space * 5, 100));
+        if (info->total_bytes >= min_metadata) {
+                spin_unlock(&info->lock);
+                return 0;
+        }
+
+        if (info->full) {
+                spin_unlock(&info->lock);
+                return 0;
+        }
+
+        if (!info->allocating_chunk) {
+                info->force_alloc = 1;
+                info->allocating_chunk = 1;
+                init_waitqueue_head(&info->allocate_wait);
+        } else {
+                wait = true;
+        }
+
+        spin_unlock(&info->lock);
+
+        if (wait) {
+                wait_event(info->allocate_wait,
+                           !info->allocating_chunk);
+                return 1;
+        }
+
+        trans = btrfs_start_transaction(root, 1);
+        if (!trans) {
+                ret = -ENOMEM;
+                goto out;
+        }
+
+        ret = do_chunk_alloc(trans, root->fs_info->extent_root,
+                             4096 + 2 * 1024 * 1024,
+                             info->flags, 0);
+        btrfs_end_transaction(trans, root);
+        if (ret)
+                goto out;
+out:
+        spin_lock(&info->lock);
+        info->allocating_chunk = 0;
+        spin_unlock(&info->lock);
+        wake_up(&info->allocate_wait);
+
+        if (ret)
+                return 0;
+        return 1;
+}
+
+/*
+ * Reserve metadata space for delalloc.
+ */
+int btrfs_reserve_metadata_for_delalloc(struct btrfs_root *root,
+                                        struct inode *inode, int num_items)
+{
+        struct btrfs_fs_info *info = root->fs_info;
+        struct btrfs_space_info *meta_sinfo;
+        u64 num_bytes;
+        u64 used;
+        u64 alloc_target;
+        int flushed = 0;
+        int force_delalloc;
+
+        /* get the space info for where the metadata will live */
+        alloc_target = btrfs_get_alloc_profile(root, 0);
+        meta_sinfo = __find_space_info(info, alloc_target);
+
+        num_bytes = calculate_bytes_needed(root->fs_info->extent_root,
+                                           num_items);
+again:
+        spin_lock(&meta_sinfo->lock);
+
+        force_delalloc = meta_sinfo->force_delalloc;
+
+        if (unlikely(!meta_sinfo->bytes_root))
+                meta_sinfo->bytes_root = calculate_bytes_needed(root, 6);
+
+        if (!flushed)
+                meta_sinfo->bytes_delalloc += num_bytes;
+
+        used = meta_sinfo->bytes_used + meta_sinfo->bytes_reserved +
+                meta_sinfo->bytes_pinned + meta_sinfo->bytes_readonly +
+                meta_sinfo->bytes_super + meta_sinfo->bytes_root +
+                meta_sinfo->bytes_may_use + meta_sinfo->bytes_delalloc;
+
+        if (used > meta_sinfo->total_bytes) {
+                flushed++;
+
+                if (flushed == 1) {
+                        if (maybe_allocate_chunk(root, meta_sinfo))
+                                goto again;
+                        flushed++;
+                } else {
                         spin_unlock(&meta_sinfo->lock);
-alloc:
-                        trans = btrfs_start_transaction(root, 1);
-                        if (!trans)
-                                return -ENOMEM;
+                }
 
-                        ret = do_chunk_alloc(trans, root->fs_info->extent_root,
-                                             2 * 1024 * 1024, alloc_target, 0);
-                        btrfs_end_transaction(trans, root);
-                        if (!meta_sinfo) {
-                                meta_sinfo = __find_space_info(info,
-                                                               alloc_target);
-                        }
+                if (flushed == 2) {
+                        filemap_flush(inode->i_mapping);
+                        goto again;
+                } else if (flushed == 3) {
+                        flush_delalloc(root, meta_sinfo);
                         goto again;
                 }
+                spin_lock(&meta_sinfo->lock);
+                meta_sinfo->bytes_delalloc -= num_bytes;
                 spin_unlock(&meta_sinfo->lock);
+                printk(KERN_ERR "enospc, has %d, reserved %d\n",
+                       BTRFS_I(inode)->outstanding_extents,
+                       BTRFS_I(inode)->reserved_extents);
+                dump_space_info(meta_sinfo, 0, 0);
+                return -ENOSPC;
+        }
 
-                if (!committed) {
-                        committed = 1;
-                        trans = btrfs_join_transaction(root, 1);
-                        if (!trans)
-                                return -ENOMEM;
-                        ret = btrfs_commit_transaction(trans, root);
-                        if (ret)
-                                return ret;
+        BTRFS_I(inode)->reserved_extents++;
+        check_force_delalloc(meta_sinfo);
+        spin_unlock(&meta_sinfo->lock);
+
+        if (!flushed && force_delalloc)
+                filemap_flush(inode->i_mapping);
+
+        return 0;
+}
+
+/*
+ * unreserve num_items number of items worth of metadata space.  This needs to
+ * be paired with btrfs_reserve_metadata_space.
+ *
+ * NOTE: if you have the option, run this _AFTER_ you do a
+ * btrfs_end_transaction, since btrfs_end_transaction will run delayed ref
+ * oprations which will result in more used metadata, so we want to make sure we
+ * can do that without issue.
+ */
+int btrfs_unreserve_metadata_space(struct btrfs_root *root, int num_items)
+{
+        struct btrfs_fs_info *info = root->fs_info;
+        struct btrfs_space_info *meta_sinfo;
+        u64 num_bytes;
+        u64 alloc_target;
+        bool bug = false;
+
+        /* get the space info for where the metadata will live */
+        alloc_target = btrfs_get_alloc_profile(root, 0);
+        meta_sinfo = __find_space_info(info, alloc_target);
+
+        num_bytes = calculate_bytes_needed(root, num_items);
+
+        spin_lock(&meta_sinfo->lock);
+        if (meta_sinfo->bytes_may_use < num_bytes) {
+                bug = true;
+                meta_sinfo->bytes_may_use = 0;
+        } else {
+                meta_sinfo->bytes_may_use -= num_bytes;
+        }
+        spin_unlock(&meta_sinfo->lock);
+
+        BUG_ON(bug);
+
+        return 0;
+}
+
+/*
+ * Reserve some metadata space for use.  We'll calculate the worste case number
+ * of bytes that would be needed to modify num_items number of items.  If we
+ * have space, fantastic, if not, you get -ENOSPC.  Please call
+ * btrfs_unreserve_metadata_space when you are done for the _SAME_ number of
+ * items you reserved, since whatever metadata you needed should have already
+ * been allocated.
+ *
+ * This will commit the transaction to make more space if we don't have enough
+ * metadata space.  THe only time we don't do this is if we're reserving space
+ * inside of a transaction, then we will just return -ENOSPC and it is the
+ * callers responsibility to handle it properly.
+ */
+int btrfs_reserve_metadata_space(struct btrfs_root *root, int num_items)
+{
+        struct btrfs_fs_info *info = root->fs_info;
+        struct btrfs_space_info *meta_sinfo;
+        u64 num_bytes;
+        u64 used;
+        u64 alloc_target;
+        int retries = 0;
+
+        /* get the space info for where the metadata will live */
+        alloc_target = btrfs_get_alloc_profile(root, 0);
+        meta_sinfo = __find_space_info(info, alloc_target);
+
+        num_bytes = calculate_bytes_needed(root, num_items);
+again:
+        spin_lock(&meta_sinfo->lock);
+
+        if (unlikely(!meta_sinfo->bytes_root))
+                meta_sinfo->bytes_root = calculate_bytes_needed(root, 6);
+
+        if (!retries)
+                meta_sinfo->bytes_may_use += num_bytes;
+
+        used = meta_sinfo->bytes_used + meta_sinfo->bytes_reserved +
+                meta_sinfo->bytes_pinned + meta_sinfo->bytes_readonly +
+                meta_sinfo->bytes_super + meta_sinfo->bytes_root +
+                meta_sinfo->bytes_may_use + meta_sinfo->bytes_delalloc;
+
+        if (used > meta_sinfo->total_bytes) {
+                retries++;
+                if (retries == 1) {
+                        if (maybe_allocate_chunk(root, meta_sinfo))
+                                goto again;
+                        retries++;
+                } else {
+                        spin_unlock(&meta_sinfo->lock);
+                }
+
+                if (retries == 2) {
+                        flush_delalloc(root, meta_sinfo);
                         goto again;
                 }
+                spin_lock(&meta_sinfo->lock);
+                meta_sinfo->bytes_may_use -= num_bytes;
+                spin_unlock(&meta_sinfo->lock);
+
+                dump_space_info(meta_sinfo, 0, 0);
                 return -ENOSPC;
         }
+
+        check_force_delalloc(meta_sinfo);
         spin_unlock(&meta_sinfo->lock);
 
         return 0;
@@ -2888,7 +3271,7 @@ alloc:
                 spin_unlock(&data_sinfo->lock);
 
                 /* commit the current transaction and try again */
-                if (!committed) {
+                if (!committed && !root->fs_info->open_ioctl_trans) {
                         committed = 1;
                         trans = btrfs_join_transaction(root, 1);
                         if (!trans)
@@ -2916,7 +3299,7 @@ alloc:
         BTRFS_I(inode)->reserved_bytes += bytes;
         spin_unlock(&data_sinfo->lock);
 
-        return btrfs_check_metadata_free_space(root);
+        return 0;
 }
 
 /*
@@ -3015,17 +3398,15 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans,
         BUG_ON(!space_info);
 
         spin_lock(&space_info->lock);
-        if (space_info->force_alloc) {
+        if (space_info->force_alloc)
                 force = 1;
-                space_info->force_alloc = 0;
-        }
         if (space_info->full) {
                 spin_unlock(&space_info->lock);
                 goto out;
         }
 
         thresh = space_info->total_bytes - space_info->bytes_readonly;
-        thresh = div_factor(thresh, 6);
+        thresh = div_factor(thresh, 8);
         if (!force &&
            (space_info->bytes_used + space_info->bytes_pinned +
             space_info->bytes_reserved + alloc_bytes) < thresh) {
@@ -3039,7 +3420,7 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans,
          * we keep a reasonable number of metadata chunks allocated in the
          * FS as well.
          */
-        if (flags & BTRFS_BLOCK_GROUP_DATA) {
+        if (flags & BTRFS_BLOCK_GROUP_DATA && fs_info->metadata_ratio) {
                 fs_info->data_chunk_allocations++;
                 if (!(fs_info->data_chunk_allocations %
                       fs_info->metadata_ratio))
@@ -3047,8 +3428,11 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans,
         }
 
         ret = btrfs_alloc_chunk(trans, extent_root, flags);
+        spin_lock(&space_info->lock);
         if (ret)
                 space_info->full = 1;
+        space_info->force_alloc = 0;
+        spin_unlock(&space_info->lock);
 out:
         mutex_unlock(&extent_root->fs_info->chunk_mutex);
         return ret;
@@ -3747,6 +4131,7 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
         int loop = 0;
         bool found_uncached_bg = false;
         bool failed_cluster_refill = false;
+        bool failed_alloc = false;
 
         WARN_ON(num_bytes < root->sectorsize);
         btrfs_set_key_type(ins, BTRFS_EXTENT_ITEM_KEY);
@@ -3951,14 +4336,23 @@ refill_cluster:
 
                 offset = btrfs_find_space_for_alloc(block_group, search_start,
                                                     num_bytes, empty_size);
-                if (!offset && (cached || (!cached &&
-                                           loop == LOOP_CACHING_NOWAIT))) {
-                        goto loop;
-                } else if (!offset && (!cached &&
-                                       loop > LOOP_CACHING_NOWAIT)) {
+                /*
+                 * If we didn't find a chunk, and we haven't failed on this
+                 * block group before, and this block group is in the middle of
+                 * caching and we are ok with waiting, then go ahead and wait
+                 * for progress to be made, and set failed_alloc to true.
+                 *
+                 * If failed_alloc is true then we've already waited on this
+                 * block group once and should move on to the next block group.
+                 */
+                if (!offset && !failed_alloc && !cached &&
+                    loop > LOOP_CACHING_NOWAIT) {
                         wait_block_group_cache_progress(block_group,
-                                        num_bytes + empty_size);
+                                                num_bytes + empty_size);
+                        failed_alloc = true;
                         goto have_block_group;
+                } else if (!offset) {
+                        goto loop;
                 }
 checks:
                 search_start = stripe_align(root, offset);
@@ -4006,6 +4400,7 @@ checks:
                 break;
 loop:
                 failed_cluster_refill = false;
+                failed_alloc = false;
                 btrfs_put_block_group(block_group);
         }
         up_read(&space_info->groups_sem);
@@ -4063,21 +4458,32 @@ loop:
         return ret;
 }
 
-static void dump_space_info(struct btrfs_space_info *info, u64 bytes)
+static void dump_space_info(struct btrfs_space_info *info, u64 bytes,
+                            int dump_block_groups)
 {
         struct btrfs_block_group_cache *cache;
 
+        spin_lock(&info->lock);
         printk(KERN_INFO "space_info has %llu free, is %sfull\n",
                (unsigned long long)(info->total_bytes - info->bytes_used -
-                                    info->bytes_pinned - info->bytes_reserved),
+                                    info->bytes_pinned - info->bytes_reserved -
+                                    info->bytes_super),
                (info->full) ? "" : "not ");
         printk(KERN_INFO "space_info total=%llu, pinned=%llu, delalloc=%llu,"
-               " may_use=%llu, used=%llu\n",
+               " may_use=%llu, used=%llu, root=%llu, super=%llu, reserved=%llu"
+               "\n",
                (unsigned long long)info->total_bytes,
                (unsigned long long)info->bytes_pinned,
                (unsigned long long)info->bytes_delalloc,
                (unsigned long long)info->bytes_may_use,
-               (unsigned long long)info->bytes_used);
+               (unsigned long long)info->bytes_used,
+               (unsigned long long)info->bytes_root,
+               (unsigned long long)info->bytes_super,
+               (unsigned long long)info->bytes_reserved);
+        spin_unlock(&info->lock);
+
+        if (!dump_block_groups)
+                return;
 
         down_read(&info->groups_sem);
         list_for_each_entry(cache, &info->block_groups, list) {
@@ -4145,7 +4551,7 @@ again:
                 printk(KERN_ERR "btrfs allocation failed flags %llu, "
                        "wanted %llu\n", (unsigned long long)data,
                        (unsigned long long)num_bytes);
-                dump_space_info(sinfo, num_bytes);
+                dump_space_info(sinfo, num_bytes, 1);
         }
 
         return ret;
@@ -4506,6 +4912,7 @@ static noinline void reada_walk_down(struct btrfs_trans_handle *trans,
         u64 bytenr;
         u64 generation;
         u64 refs;
+        u64 flags;
         u64 last = 0;
         u32 nritems;
         u32 blocksize;
@@ -4543,15 +4950,19 @@ static noinline void reada_walk_down(struct btrfs_trans_handle *trans,
                     generation <= root->root_key.offset)
                         continue;
 
+                /* We don't lock the tree block, it's OK to be racy here */
+                ret = btrfs_lookup_extent_info(trans, root, bytenr, blocksize,
+                                               &refs, &flags);
+                BUG_ON(ret);
+                BUG_ON(refs == 0);
+
                 if (wc->stage == DROP_REFERENCE) {
-                        ret = btrfs_lookup_extent_info(trans, root,
-                                                bytenr, blocksize,
-                                                &refs, NULL);
-                        BUG_ON(ret);
-                        BUG_ON(refs == 0);
                         if (refs == 1)
                                 goto reada;
 
+                        if (wc->level == 1 &&
+                            (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF))
+                                continue;
                         if (!wc->update_ref ||
                             generation <= root->root_key.offset)
                                 continue;
@@ -4560,6 +4971,10 @@ static noinline void reada_walk_down(struct btrfs_trans_handle *trans,
                                                   &wc->update_progress);
                         if (ret < 0)
                                 continue;
+                } else {
+                        if (wc->level == 1 &&
+                            (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF))
+                                continue;
                 }
 reada:
                 ret = readahead_tree_block(root, bytenr, blocksize,
@@ -4583,7 +4998,7 @@ reada:
 static noinline int walk_down_proc(struct btrfs_trans_handle *trans,
                                    struct btrfs_root *root,
                                    struct btrfs_path *path,
-                                   struct walk_control *wc)
+                                   struct walk_control *wc, int lookup_info)
 {
         int level = wc->level;
         struct extent_buffer *eb = path->nodes[level];
@@ -4598,8 +5013,9 @@ static noinline int walk_down_proc(struct btrfs_trans_handle *trans,
          * when reference count of tree block is 1, it won't increase
          * again. once full backref flag is set, we never clear it.
          */
-        if ((wc->stage == DROP_REFERENCE && wc->refs[level] != 1) ||
-            (wc->stage == UPDATE_BACKREF && !(wc->flags[level] & flag))) {
+        if (lookup_info &&
+            ((wc->stage == DROP_REFERENCE && wc->refs[level] != 1) ||
+             (wc->stage == UPDATE_BACKREF && !(wc->flags[level] & flag)))) {
                 BUG_ON(!path->locks[level]);
                 ret = btrfs_lookup_extent_info(trans, root,
                                                eb->start, eb->len,
@@ -4660,7 +5076,7 @@ static noinline int walk_down_proc(struct btrfs_trans_handle *trans,
 static noinline int do_walk_down(struct btrfs_trans_handle *trans,
                                  struct btrfs_root *root,
                                  struct btrfs_path *path,
-                                 struct walk_control *wc)
+                                 struct walk_control *wc, int *lookup_info)
 {
         u64 bytenr;
         u64 generation;
@@ -4680,8 +5096,10 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
          * for the subtree
          */
         if (wc->stage == UPDATE_BACKREF &&
-            generation <= root->root_key.offset)
+            generation <= root->root_key.offset) {
+                *lookup_info = 1;
                 return 1;
+        }
 
         bytenr = btrfs_node_blockptr(path->nodes[level], path->slots[level]);
         blocksize = btrfs_level_size(root, level - 1);
@@ -4694,14 +5112,19 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
         btrfs_tree_lock(next);
         btrfs_set_lock_blocking(next);
 
-        if (wc->stage == DROP_REFERENCE) {
-                ret = btrfs_lookup_extent_info(trans, root, bytenr, blocksize,
-                                               &wc->refs[level - 1],
-                                               &wc->flags[level - 1]);
-                BUG_ON(ret);
-                BUG_ON(wc->refs[level - 1] == 0);
+        ret = btrfs_lookup_extent_info(trans, root, bytenr, blocksize,
+                                       &wc->refs[level - 1],
+                                       &wc->flags[level - 1]);
+        BUG_ON(ret);
+        BUG_ON(wc->refs[level - 1] == 0);
+        *lookup_info = 0;
 
+        if (wc->stage == DROP_REFERENCE) {
                 if (wc->refs[level - 1] > 1) {
+                        if (level == 1 &&
+                            (wc->flags[0] & BTRFS_BLOCK_FLAG_FULL_BACKREF))
+                                goto skip;
+
                         if (!wc->update_ref ||
                             generation <= root->root_key.offset)
                                 goto skip;
@@ -4715,12 +5138,17 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
                         wc->stage = UPDATE_BACKREF;
                         wc->shared_level = level - 1;
                 }
+        } else {
+                if (level == 1 &&
+                    (wc->flags[0] & BTRFS_BLOCK_FLAG_FULL_BACKREF))
+                        goto skip;
         }
 
         if (!btrfs_buffer_uptodate(next, generation)) {
                 btrfs_tree_unlock(next);
                 free_extent_buffer(next);
                 next = NULL;
+                *lookup_info = 1;
         }
 
         if (!next) {
@@ -4743,21 +5171,22 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
 skip:
         wc->refs[level - 1] = 0;
         wc->flags[level - 1] = 0;
+        if (wc->stage == DROP_REFERENCE) {
+                if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF) {
+                        parent = path->nodes[level]->start;
+                } else {
+                        BUG_ON(root->root_key.objectid !=
+                               btrfs_header_owner(path->nodes[level]));
+                        parent = 0;
+                }
 
-        if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF) {
-                parent = path->nodes[level]->start;
-        } else {
-                BUG_ON(root->root_key.objectid !=
-                       btrfs_header_owner(path->nodes[level]));
-                parent = 0;
+                ret = btrfs_free_extent(trans, root, bytenr, blocksize, parent,
+                                        root->root_key.objectid, level - 1, 0);
+                BUG_ON(ret);
         }
-
-        ret = btrfs_free_extent(trans, root, bytenr, blocksize, parent,
-                                root->root_key.objectid, level - 1, 0);
-        BUG_ON(ret);
-
         btrfs_tree_unlock(next);
         free_extent_buffer(next);
+        *lookup_info = 1;
         return 1;
 }
 
@@ -4871,6 +5300,7 @@ static noinline int walk_down_tree(struct btrfs_trans_handle *trans,
                                    struct walk_control *wc)
 {
         int level = wc->level;
+        int lookup_info = 1;
         int ret;
 
         while (level >= 0) {
@@ -4878,14 +5308,14 @@ static noinline int walk_down_tree(struct btrfs_trans_handle *trans,
                     btrfs_header_nritems(path->nodes[level]))
                         break;
 
-                ret = walk_down_proc(trans, root, path, wc);
+                ret = walk_down_proc(trans, root, path, wc, lookup_info);
                 if (ret > 0)
                         break;
 
                 if (level == 0)
                         break;
 
-                ret = do_walk_down(trans, root, path, wc);
+                ret = do_walk_down(trans, root, path, wc, &lookup_info);
                 if (ret > 0) {
                         path->slots[level]++;
                         continue;