[PATCH 1/2] Btrfs: fix OOPS of empty filesystem after balance

[liubo <liubo2009@cn.fujitsu.com>]

btrfs will remove unused block groups after balance.
When a empty filesystem is balanced, the block group with tag "DATA" may be
dropped, and after umount and mount again, it will not find "DATA" space_info
and lead to OOPS.
So we initial the necessary space_infos(DATA, SYSTEM, METADATA) to avoid OOPS.

Reported-by: Daniel J Blueman <daniel.blueman@gmail.com>
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
---
 fs/btrfs/ctree.h       |    1 +
 fs/btrfs/disk-io.c     |    6 ++++++
 fs/btrfs/extent-tree.c |   23 +++++++++++++++++++++++
 3 files changed, 30 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 28188a7..49c50e5 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2221,6 +2221,7 @@ int btrfs_error_discard_extent(struct btrfs_root *root, u64 bytenr,
 			       u64 num_bytes);
 int btrfs_force_chunk_alloc(struct btrfs_trans_handle *trans,
 			    struct btrfs_root *root, u64 type);
+int btrfs_init_space_info(struct btrfs_fs_info *fs_info);
 
 /* ctree.c */
 int btrfs_bin_search(struct extent_buffer *eb, struct btrfs_key *key,
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3e1ea3e..8bcdc62 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1967,6 +1967,12 @@ struct btrfs_root *open_ctree(struct super_block *sb,
 	fs_info->metadata_alloc_profile = (u64)-1;
 	fs_info->system_alloc_profile = fs_info->metadata_alloc_profile;
 
+	ret = btrfs_init_space_info(fs_info);
+	if (ret) {
+		printk(KERN_ERR "Failed to initial space info: %d\n", ret);
+		goto fail_block_groups;
+	}
+
 	ret = btrfs_read_block_groups(extent_root);
 	if (ret) {
 		printk(KERN_ERR "Failed to read block groups: %d\n", ret);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 100e409..08525ee 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -8714,6 +8714,29 @@ out:
 	return ret;
 }
 
+int btrfs_init_space_info(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_space_info *space_info;
+	int ret;
+
+	ret = update_space_info(fs_info, BTRFS_BLOCK_GROUP_SYSTEM, 0, 0,
+								 &space_info);
+	if (ret)
+		return ret;
+
+	ret = update_space_info(fs_info, BTRFS_BLOCK_GROUP_METADATA, 0, 0,
+								 &space_info);
+	if (ret)
+		return ret;
+
+	ret = update_space_info(fs_info, BTRFS_BLOCK_GROUP_DATA, 0, 0,
+								 &space_info);
+	if (ret)
+		return ret;
+
+	return ret;
+}
+
 int btrfs_error_unpin_extent_range(struct btrfs_root *root, u64 start, u64 end)
 {
 	return unpin_extent_range(root, start, end);
-- 
1.6.5.2