13 files changed, 188 insertions, 43 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index ecd25a1b4e51..ca9d8f1a3bb6 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -651,6 +651,8 @@ tree_mod_log_insert_root(struct btrfs_fs_info *fs_info,
         if (tree_mod_dont_log(fs_info, NULL))
                 return 0;
 
+        __tree_mod_log_free_eb(fs_info, old_root);
+
         ret = tree_mod_alloc(fs_info, flags, &tm);
         if (ret < 0)
                 goto out;
@@ -736,7 +738,7 @@ tree_mod_log_search(struct btrfs_fs_info *fs_info, u64 start, u64 min_seq)
 static noinline void
 tree_mod_log_eb_copy(struct btrfs_fs_info *fs_info, struct extent_buffer *dst,
                      struct extent_buffer *src, unsigned long dst_offset,
-                     unsigned long src_offset, int nr_items)
+                     unsigned long src_offset, int nr_items, int log_removal)
 {
         int ret;
         int i;
@@ -750,10 +752,12 @@ tree_mod_log_eb_copy(struct btrfs_fs_info *fs_info, struct extent_buffer *dst,
         }
 
         for (i = 0; i < nr_items; i++) {
-                ret = tree_mod_log_insert_key_locked(fs_info, src,
-                                                     i + src_offset,
-                                                     MOD_LOG_KEY_REMOVE);
-                BUG_ON(ret < 0);
+                if (log_removal) {
+                        ret = tree_mod_log_insert_key_locked(fs_info, src,
+                                                        i + src_offset,
+                                                        MOD_LOG_KEY_REMOVE);
+                        BUG_ON(ret < 0);
+                }
                 ret = tree_mod_log_insert_key_locked(fs_info, dst,
                                                      i + dst_offset,
                                                      MOD_LOG_KEY_ADD);
@@ -927,7 +931,6 @@ static noinline int update_ref_for_cow(struct btrfs_trans_handle *trans,
                         ret = btrfs_dec_ref(trans, root, buf, 1, 1);
                         BUG_ON(ret); /* -ENOMEM */
                 }
-                tree_mod_log_free_eb(root->fs_info, buf);
                 clean_tree_block(trans, root, buf);
                 *last_ref = 1;
         }
@@ -1046,6 +1049,7 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
                 btrfs_set_node_ptr_generation(parent, parent_slot,
                                               trans->transid);
                 btrfs_mark_buffer_dirty(parent);
+                tree_mod_log_free_eb(root->fs_info, buf);
                 btrfs_free_tree_block(trans, root, buf, parent_start,
                                       last_ref);
         }
@@ -1750,7 +1754,6 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
                         goto enospc;
                 }
 
-                tree_mod_log_free_eb(root->fs_info, root->node);
                 tree_mod_log_set_root_pointer(root, child);
                 rcu_assign_pointer(root->node, child);
 
@@ -2995,7 +2998,7 @@ static int push_node_left(struct btrfs_trans_handle *trans,
                 push_items = min(src_nritems - 8, push_items);
 
         tree_mod_log_eb_copy(root->fs_info, dst, src, dst_nritems, 0,
-                             push_items);
+                             push_items, 1);
         copy_extent_buffer(dst, src,
                            btrfs_node_key_ptr_offset(dst_nritems),
                            btrfs_node_key_ptr_offset(0),
@@ -3066,7 +3069,7 @@ static int balance_node_right(struct btrfs_trans_handle *trans,
                                       sizeof(struct btrfs_key_ptr));
 
         tree_mod_log_eb_copy(root->fs_info, dst, src, 0,
-                             src_nritems - push_items, push_items);
+                             src_nritems - push_items, push_items, 1);
         copy_extent_buffer(dst, src,
                            btrfs_node_key_ptr_offset(0),
                            btrfs_node_key_ptr_offset(src_nritems - push_items),
@@ -3218,12 +3221,18 @@ static noinline int split_node(struct btrfs_trans_handle *trans,
         int mid;
         int ret;
         u32 c_nritems;
+        int tree_mod_log_removal = 1;
 
         c = path->nodes[level];
         WARN_ON(btrfs_header_generation(c) != trans->transid);
         if (c == root->node) {
                 /* trying to split the root, lets make a new one */
                 ret = insert_new_root(trans, root, path, level + 1);
+                /*
+                 * removal of root nodes has been logged by
+                 * tree_mod_log_set_root_pointer due to locking
+                 */
+                tree_mod_log_removal = 0;
                 if (ret)
                         return ret;
         } else {
@@ -3261,7 +3270,8 @@ static noinline int split_node(struct btrfs_trans_handle *trans,
                             (unsigned long)btrfs_header_chunk_tree_uuid(split),
                             BTRFS_UUID_SIZE);
 
-        tree_mod_log_eb_copy(root->fs_info, split, c, 0, mid, c_nritems - mid);
+        tree_mod_log_eb_copy(root->fs_info, split, c, 0, mid, c_nritems - mid,
+                             tree_mod_log_removal);
         copy_extent_buffer(split, c,
                            btrfs_node_key_ptr_offset(0),
                            btrfs_node_key_ptr_offset(mid),
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 7d84651e850b..6d19a0a554aa 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1291,6 +1291,7 @@ struct btrfs_root *btrfs_create_tree(struct btrfs_trans_handle *trans,
                                       0, objectid, NULL, 0, 0, 0);
         if (IS_ERR(leaf)) {
                 ret = PTR_ERR(leaf);
+                leaf = NULL;
                 goto fail;
         }
 
@@ -1334,11 +1335,16 @@ struct btrfs_root *btrfs_create_tree(struct btrfs_trans_handle *trans,
 
         btrfs_tree_unlock(leaf);
 
+        return root;
+
 fail:
-        if (ret)
-                return ERR_PTR(ret);
+        if (leaf) {
+                btrfs_tree_unlock(leaf);
+                free_extent_buffer(leaf);
+        }
+        kfree(root);
 
-        return root;
+        return ERR_PTR(ret);
 }
 
 static struct btrfs_root *alloc_log_tree(struct btrfs_trans_handle *trans,
@@ -3253,7 +3259,7 @@ void btrfs_free_fs_root(struct btrfs_fs_info *fs_info, struct btrfs_root *root)
         if (btrfs_root_refs(&root->root_item) == 0)
                 synchronize_srcu(&fs_info->subvol_srcu);
 
-        if (fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) {
+        if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) {
                 btrfs_free_log(NULL, root);
                 btrfs_free_log_root_tree(NULL, fs_info);
         }
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 9ac2eca681eb..3d551231caba 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -257,7 +257,8 @@ static int exclude_super_stripes(struct btrfs_root *root,
                 cache->bytes_super += stripe_len;
                 ret = add_excluded_extent(root, cache->key.objectid,
                                           stripe_len);
-                BUG_ON(ret); /* -ENOMEM */
+                if (ret)
+                        return ret;
         }
 
         for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
@@ -265,13 +266,17 @@ static int exclude_super_stripes(struct btrfs_root *root,
                 ret = btrfs_rmap_block(&root->fs_info->mapping_tree,
                                        cache->key.objectid, bytenr,
                                        0, &logical, &nr, &stripe_len);
-                BUG_ON(ret); /* -ENOMEM */
+                if (ret)
+                        return ret;
 
                 while (nr--) {
                         cache->bytes_super += stripe_len;
                         ret = add_excluded_extent(root, logical[nr],
                                                   stripe_len);
-                        BUG_ON(ret); /* -ENOMEM */
+                        if (ret) {
+                                kfree(logical);
+                                return ret;
+                        }
                 }
 
                 kfree(logical);
@@ -4438,7 +4443,7 @@ static void update_global_block_rsv(struct btrfs_fs_info *fs_info)
         spin_lock(&sinfo->lock);
         spin_lock(&block_rsv->lock);
 
-        block_rsv->size = num_bytes;
+        block_rsv->size = min_t(u64, num_bytes, 512 * 1024 * 1024);
 
         num_bytes = sinfo->bytes_used + sinfo->bytes_pinned +
                     sinfo->bytes_reserved + sinfo->bytes_readonly +
@@ -4793,14 +4798,49 @@ out_fail:
          * If the inodes csum_bytes is the same as the original
          * csum_bytes then we know we haven't raced with any free()ers
          * so we can just reduce our inodes csum bytes and carry on.
-         * Otherwise we have to do the normal free thing to account for
-         * the case that the free side didn't free up its reserve
-         * because of this outstanding reservation.
          */
-        if (BTRFS_I(inode)->csum_bytes == csum_bytes)
+        if (BTRFS_I(inode)->csum_bytes == csum_bytes) {
                 calc_csum_metadata_size(inode, num_bytes, 0);
-        else
-                to_free = calc_csum_metadata_size(inode, num_bytes, 0);
+        } else {
+                u64 orig_csum_bytes = BTRFS_I(inode)->csum_bytes;
+                u64 bytes;
+
+                /*
+                 * This is tricky, but first we need to figure out how much we
+                 * free'd from any free-ers that occured during this
+                 * reservation, so we reset ->csum_bytes to the csum_bytes
+                 * before we dropped our lock, and then call the free for the
+                 * number of bytes that were freed while we were trying our
+                 * reservation.
+                 */
+                bytes = csum_bytes - BTRFS_I(inode)->csum_bytes;
+                BTRFS_I(inode)->csum_bytes = csum_bytes;
+                to_free = calc_csum_metadata_size(inode, bytes, 0);
+
+
+                /*
+                 * Now we need to see how much we would have freed had we not
+                 * been making this reservation and our ->csum_bytes were not
+                 * artificially inflated.
+                 */
+                BTRFS_I(inode)->csum_bytes = csum_bytes - num_bytes;
+                bytes = csum_bytes - orig_csum_bytes;
+                bytes = calc_csum_metadata_size(inode, bytes, 0);
+
+                /*
+                 * Now reset ->csum_bytes to what it should be.  If bytes is
+                 * more than to_free then we would have free'd more space had we
+                 * not had an artificially high ->csum_bytes, so we need to free
+                 * the remainder.  If bytes is the same or less then we don't
+                 * need to do anything, the other free-ers did the correct
+                 * thing.
+                 */
+                BTRFS_I(inode)->csum_bytes = orig_csum_bytes - num_bytes;
+                if (bytes > to_free)
+                        to_free = bytes - to_free;
+                else
+                        to_free = 0;
+        }
         spin_unlock(&BTRFS_I(inode)->lock);
         if (dropped)
                 to_free += btrfs_calc_trans_metadata_size(root, dropped);
@@ -7947,7 +7987,17 @@ int btrfs_read_block_groups(struct btrfs_root *root)
                  * info has super bytes accounted for, otherwise we'll think
                  * we have more space than we actually do.
                  */
-                exclude_super_stripes(root, cache);
+                ret = exclude_super_stripes(root, cache);
+                if (ret) {
+                        /*
+                         * We may have excluded something, so call this just in
+                         * case.
+                         */
+                        free_excluded_extents(root, cache);
+                        kfree(cache->free_space_ctl);
+                        kfree(cache);
+                        goto error;
+                }
 
                 /*
                  * check for two cases, either we are full, and therefore
@@ -8089,7 +8139,17 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans,
 
         cache->last_byte_to_unpin = (u64)-1;
         cache->cached = BTRFS_CACHE_FINISHED;
-        exclude_super_stripes(root, cache);
+        ret = exclude_super_stripes(root, cache);
+        if (ret) {
+                /*
+                 * We may have excluded something, so call this just in
+                 * case.
+                 */
+                free_excluded_extents(root, cache);
+                kfree(cache->free_space_ctl);
+                kfree(cache);
+                return ret;
+        }
 
         add_new_free_space(cache, root->fs_info, chunk_offset,
                            chunk_offset + size);
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index f173c5af6461..cdee391fc7bf 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1257,6 +1257,39 @@ int unlock_extent(struct extent_io_tree *tree, u64 start, u64 end)
                                 GFP_NOFS);
 }
 
+int extent_range_clear_dirty_for_io(struct inode *inode, u64 start, u64 end)
+{
+        unsigned long index = start >> PAGE_CACHE_SHIFT;
+        unsigned long end_index = end >> PAGE_CACHE_SHIFT;
+        struct page *page;
+
+        while (index <= end_index) {
+                page = find_get_page(inode->i_mapping, index);
+                BUG_ON(!page); /* Pages should be in the extent_io_tree */
+                clear_page_dirty_for_io(page);
+                page_cache_release(page);
+                index++;
+        }
+        return 0;
+}
+
+int extent_range_redirty_for_io(struct inode *inode, u64 start, u64 end)
+{
+        unsigned long index = start >> PAGE_CACHE_SHIFT;
+        unsigned long end_index = end >> PAGE_CACHE_SHIFT;
+        struct page *page;
+
+        while (index <= end_index) {
+                page = find_get_page(inode->i_mapping, index);
+                BUG_ON(!page); /* Pages should be in the extent_io_tree */
+                account_page_redirty(page);
+                __set_page_dirty_nobuffers(page);
+                page_cache_release(page);
+                index++;
+        }
+        return 0;
+}
+
 /*
  * helper function to set both pages and extents in the tree writeback
  */
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 6068a1985560..258c92156857 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -325,6 +325,8 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long offset,
                       unsigned long *map_len);
 int extent_range_uptodate(struct extent_io_tree *tree,
                           u64 start, u64 end);
+int extent_range_clear_dirty_for_io(struct inode *inode, u64 start, u64 end);
+int extent_range_redirty_for_io(struct inode *inode, u64 start, u64 end);
 int extent_clear_unlock_delalloc(struct inode *inode,
                                 struct extent_io_tree *tree,
                                 u64 start, u64 end, struct page *locked_page,
diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index ec160202be3e..c4628a201cb3 100644
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -118,9 +118,11 @@ struct btrfs_csum_item *btrfs_lookup_csum(struct btrfs_trans_handle *trans,
                 csums_in_item = btrfs_item_size_nr(leaf, path->slots[0]);
                 csums_in_item /= csum_size;
 
-                if (csum_offset >= csums_in_item) {
+                if (csum_offset == csums_in_item) {
                         ret = -EFBIG;
                         goto fail;
+                } else if (csum_offset > csums_in_item) {
+                        goto fail;
                 }
         }
         item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_csum_item);
@@ -728,7 +730,6 @@ int btrfs_csum_file_blocks(struct btrfs_trans_handle *trans,
                 return -ENOMEM;
 
         sector_sum = sums->sums;
-        trans->adding_csums = 1;
 again:
         next_offset = (u64)-1;
         found_next = 0;
@@ -899,7 +900,6 @@ next_sector:
                 goto again;
         }
 out:
-        trans->adding_csums = 0;
         btrfs_free_path(path);
         return ret;
 
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 5b4ea5f55b8f..ade03e6f7bd2 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2142,6 +2142,7 @@ static long btrfs_fallocate(struct file *file, int mode,
 {
         struct inode *inode = file_inode(file);
         struct extent_state *cached_state = NULL;
+        struct btrfs_root *root = BTRFS_I(inode)->root;
         u64 cur_offset;
         u64 last_byte;
         u64 alloc_start;
@@ -2169,6 +2170,11 @@ static long btrfs_fallocate(struct file *file, int mode,
         ret = btrfs_check_data_free_space(inode, alloc_end - alloc_start);
         if (ret)
                 return ret;
+        if (root->fs_info->quota_enabled) {
+                ret = btrfs_qgroup_reserve(root, alloc_end - alloc_start);
+                if (ret)
+                        goto out_reserve_fail;
+        }
 
         /*
          * wait for ordered IO before we have any locks.  We'll loop again
@@ -2272,6 +2278,9 @@ static long btrfs_fallocate(struct file *file, int mode,
                              &cached_state, GFP_NOFS);
 out:
         mutex_unlock(&inode->i_mutex);
+        if (root->fs_info->quota_enabled)
+                btrfs_qgroup_free(root, alloc_end - alloc_start);
+out_reserve_fail:
         /* Let go of our reservation. */
         btrfs_free_reserved_data_space(inode, alloc_end - alloc_start);
         return ret;
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index ca1b767d51f7..09c58a35b429 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -353,6 +353,7 @@ static noinline int compress_file_range(struct inode *inode,
         int i;
         int will_compress;
         int compress_type = root->fs_info->compress_type;
+        int redirty = 0;
 
         /* if this is a small write inside eof, kick off a defrag */
         if ((end - start + 1) < 16 * 1024 &&
@@ -415,6 +416,17 @@ again:
                 if (BTRFS_I(inode)->force_compress)
                         compress_type = BTRFS_I(inode)->force_compress;
 
+                /*
+                 * we need to call clear_page_dirty_for_io on each
+                 * page in the range.  Otherwise applications with the file
+                 * mmap'd can wander in and change the page contents while
+                 * we are compressing them.
+                 *
+                 * If the compression fails for any reason, we set the pages
+                 * dirty again later on.
+                 */
+                extent_range_clear_dirty_for_io(inode, start, end);
+                redirty = 1;
                 ret = btrfs_compress_pages(compress_type,
                                            inode->i_mapping, start,
                                            total_compressed, pages,
@@ -554,6 +566,8 @@ cleanup_and_bail_uncompressed:
                         __set_page_dirty_nobuffers(locked_page);
                         /* unlocked later on in the async handlers */
                 }
+                if (redirty)
+                        extent_range_redirty_for_io(inode, start, end);
                 add_async_extent(async_cow, start, end - start + 1,
                                  0, NULL, 0, BTRFS_COMPRESS_NONE);
                 *num_added += 1;
@@ -1743,8 +1757,10 @@ static noinline int add_pending_csums(struct btrfs_trans_handle *trans,
         struct btrfs_ordered_sum *sum;
 
         list_for_each_entry(sum, list, list) {
+                trans->adding_csums = 1;
                 btrfs_csum_file_blocks(trans,
                        BTRFS_I(inode)->root->fs_info->csum_root, sum);
+                trans->adding_csums = 0;
         }
         return 0;
 }
@@ -3679,11 +3695,9 @@ static struct btrfs_trans_handle *__unlink_start_trans(struct inode *dir,
          * 1 for the dir item
          * 1 for the dir index
          * 1 for the inode ref
-         * 1 for the inode ref in the tree log
-         * 2 for the dir entries in the log
          * 1 for the inode
          */
-        trans = btrfs_start_transaction(root, 8);
+        trans = btrfs_start_transaction(root, 5);
         if (!IS_ERR(trans) || PTR_ERR(trans) != -ENOSPC)
                 return trans;
 
@@ -8127,7 +8141,7 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
          * inodes.  So 5 * 2 is 10, plus 1 for the new link, so 11 total items
          * should cover the worst case number of items we'll modify.
          */
-        trans = btrfs_start_transaction(root, 20);
+        trans = btrfs_start_transaction(root, 11);
         if (IS_ERR(trans)) {
                 ret = PTR_ERR(trans);
                 goto out_notrans;
diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index dc08d77b717e..005c45db699e 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -557,6 +557,7 @@ void btrfs_wait_ordered_extents(struct btrfs_root *root, int delay_iput)
         INIT_LIST_HEAD(&splice);
         INIT_LIST_HEAD(&works);
 
+        mutex_lock(&root->fs_info->ordered_operations_mutex);
         spin_lock(&root->fs_info->ordered_extent_lock);
         list_splice_init(&root->fs_info->ordered_extents, &splice);
         while (!list_empty(&splice)) {
@@ -600,6 +601,7 @@ void btrfs_wait_ordered_extents(struct btrfs_root *root, int delay_iput)
 
                 cond_resched();
         }
+        mutex_unlock(&root->fs_info->ordered_operations_mutex);
 }
 
 /*
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 5471e47d6559..b44124dd2370 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1153,7 +1153,7 @@ int btrfs_qgroup_account_ref(struct btrfs_trans_handle *trans,
         ret = btrfs_find_all_roots(trans, fs_info, node->bytenr,
                                    sgn > 0 ? node->seq - 1 : node->seq, &roots);
         if (ret < 0)
-                goto out;
+                return ret;
 
         spin_lock(&fs_info->qgroup_lock);
         quota_root = fs_info->quota_root;
@@ -1275,7 +1275,6 @@ int btrfs_qgroup_account_ref(struct btrfs_trans_handle *trans,
         ret = 0;
 unlock:
         spin_unlock(&fs_info->qgroup_lock);
-out:
         ulist_free(roots);
         ulist_free(tmp);
 
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 53c3501fa4ca..85e072b956d5 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -542,7 +542,6 @@ static void scrub_print_warning(const char *errstr, struct scrub_block *sblock)
         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 {
@@ -558,7 +557,9 @@ static void scrub_print_warning(const char *errstr, struct scrub_block *sblock)
                                 ret < 0 ? -1 : ref_level,
                                 ret < 0 ? -1 : ref_root);
                 } while (ret != 1);
+                btrfs_release_path(path);
         } else {
+                btrfs_release_path(path);
                 swarn.path = path;
                 swarn.dev = dev;
                 iterate_extent_inodes(fs_info, found_key.objectid,
diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index f7a8b861058b..c85e7c6b4598 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -3945,12 +3945,10 @@ static int is_extent_unchanged(struct send_ctx *sctx,
                     found_key.type != key.type) {
                         key.offset += right_len;
                         break;
-                } else {
-                        if (found_key.offset != key.offset + right_len) {
-                                /* Should really not happen */
-                                ret = -EIO;
-                                goto out;
-                        }
+                }
+                if (found_key.offset != key.offset + right_len) {
+                        ret = 0;
+                        goto out;
                 }
                 key = found_key;
         }
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 5989a92236f7..2854c824ab64 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4935,7 +4935,18 @@ int btrfs_rmap_block(struct btrfs_mapping_tree *map_tree,
         em = lookup_extent_mapping(em_tree, chunk_start, 1);
         read_unlock(&em_tree->lock);
 
-        BUG_ON(!em || em->start != chunk_start);
+        if (!em) {
+                printk(KERN_ERR "btrfs: couldn't find em for chunk %Lu\n",
+                       chunk_start);
+                return -EIO;
+        }
+
+        if (em->start != chunk_start) {
+                printk(KERN_ERR "btrfs: bad chunk start, em=%Lu, wanted=%Lu\n",
+                       em->start, chunk_start);
+                free_extent_map(em);
+                return -EIO;
+        }
         map = (struct map_lookup *)em->bdev;
 
         length = em->len;