Btrfs: Fix super block updates during transaction commit

The super block written during commit was not consistent with the state of
the trees.  This change adds an in-memory copy of the super so that we can
make sure to write out consistent data during a commit.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/ctree.h

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index fb6fffb..1998f86 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -306,6 +306,7 @@
 	u64 generation;
 	struct btrfs_transaction *running_transaction;
 	struct btrfs_super_block *disk_super;
+	struct btrfs_super_block super_copy;
 	struct buffer_head *sb_buffer;
 	struct super_block *sb;
 	struct inode *btree_inode;

fs/btrfs/disk-io.c

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index d7615e1..7081729 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -471,6 +471,8 @@
 	if (!fs_info->sb_buffer)
 		goto fail_iput;
 	disk_super = (struct btrfs_super_block *)fs_info->sb_buffer->b_data;
+	fs_info->disk_super = disk_super;
+	memcpy(&fs_info->super_copy, disk_super, sizeof(fs_info->super_copy));
 
 	if (!btrfs_super_root(disk_super))
 		goto fail_sb_buffer;
@@ -479,7 +481,6 @@
 		     btrfs_super_total_blocks(disk_super) <<
 		     fs_info->btree_inode->i_blkbits);
 
-	fs_info->disk_super = disk_super;
 
 	if (strncmp((char *)(&disk_super->magic), BTRFS_MAGIC,
 		    sizeof(disk_super->magic))) {
@@ -527,8 +528,6 @@
 	int ret;
 	struct buffer_head *bh = root->fs_info->sb_buffer;
 
-	btrfs_set_super_root(root->fs_info->disk_super,
-			     bh_blocknr(root->fs_info->tree_root->node));
 	lock_buffer(bh);
 	WARN_ON(atomic_read(&bh->b_count) < 1);
 	clear_buffer_dirty(bh);

fs/btrfs/extent-tree.c

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 8025e9f..7e55034 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -796,8 +796,8 @@
 
 	for (i = 0; i < extent_root->fs_info->extent_tree_insert_nr; i++) {
 		ins.objectid = extent_root->fs_info->extent_tree_insert[i];
-		super_blocks_used = btrfs_super_blocks_used(info->disk_super);
-		btrfs_set_super_blocks_used(info->disk_super,
+		super_blocks_used = btrfs_super_blocks_used(&info->super_copy);
+		btrfs_set_super_blocks_used(&info->super_copy,
 					    super_blocks_used + 1);
 		ret = btrfs_insert_item(trans, extent_root, &ins, &extent_item,
 					sizeof(extent_item));
@@ -892,8 +892,8 @@
 			BUG_ON(ret);
 		}
 
-		super_blocks_used = btrfs_super_blocks_used(info->disk_super);
-		btrfs_set_super_blocks_used(info->disk_super,
+		super_blocks_used = btrfs_super_blocks_used(&info->super_copy);
+		btrfs_set_super_blocks_used(&info->super_copy,
 					    super_blocks_used - num_blocks);
 		ret = btrfs_del_item(trans, extent_root, path);
 		if (ret) {
@@ -1032,7 +1032,7 @@
 		info->extent_tree_prealloc_nr = 0;
 	}
 	if (search_end == (u64)-1)
-		search_end = btrfs_super_total_blocks(info->disk_super);
+		search_end = btrfs_super_total_blocks(&info->super_copy);
 	if (hint_block) {
 		block_group = btrfs_lookup_block_group(info, hint_block);
 		block_group = btrfs_find_block_group(root, block_group,
@@ -1361,8 +1361,8 @@
 		}
 	}
 
-	super_blocks_used = btrfs_super_blocks_used(info->disk_super);
-	btrfs_set_super_blocks_used(info->disk_super, super_blocks_used +
+	super_blocks_used = btrfs_super_blocks_used(&info->super_copy);
+	btrfs_set_super_blocks_used(&info->super_copy, super_blocks_used +
 				    num_blocks);
 	ret = btrfs_insert_item(trans, extent_root, ins, &extent_item,
 				sizeof(extent_item));
@@ -1737,7 +1737,7 @@
 					   BTRFS_BLOCK_GROUP_AVAIL);
 		}
 		if (key.objectid >=
-		    btrfs_super_total_blocks(info->disk_super))
+		    btrfs_super_total_blocks(&info->super_copy))
 			break;
 	}
 

fs/btrfs/super.c

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index c11ecf5..2e797d5 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -144,7 +144,7 @@
 static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 {
 	struct btrfs_root *root = btrfs_sb(dentry->d_sb);
-	struct btrfs_super_block *disk_super = root->fs_info->disk_super;
+	struct btrfs_super_block *disk_super = &root->fs_info->super_copy;
 
 	buf->f_namelen = BTRFS_NAME_LEN;
 	buf->f_blocks = btrfs_super_total_blocks(disk_super);

fs/btrfs/transaction.c

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index a5a63d4..3b2face 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -380,6 +380,12 @@
 		else
 			prev_trans->use_count++;
 	}
+	btrfs_set_super_generation(&root->fs_info->super_copy,
+				   cur_trans->transid);
+	btrfs_set_super_root(&root->fs_info->super_copy,
+			     bh_blocknr(root->fs_info->tree_root->node));
+	memcpy(root->fs_info->disk_super, &root->fs_info->super_copy,
+	       sizeof(root->fs_info->super_copy));
 	mutex_unlock(&root->fs_info->trans_mutex);
 	mutex_unlock(&root->fs_info->fs_mutex);
 	ret = btrfs_write_and_wait_transaction(trans, root);
@@ -389,8 +395,6 @@
 		put_transaction(prev_trans);
 		mutex_unlock(&root->fs_info->trans_mutex);
 	}
-	btrfs_set_super_generation(root->fs_info->disk_super,
-				   cur_trans->transid);
 	BUG_ON(ret);
 	write_ctree_super(trans, root);