Btrfs: Fix crash on read failures at mount

If the tree roots hit read errors during mount, btrfs is not properly
erroring out.  We need to check the uptodate bits after
reading in the tree root node.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 0d50d49..55d9d18 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1783,6 +1783,11 @@
 					   btrfs_super_chunk_root(disk_super),
 					   blocksize, generation);
 	BUG_ON(!chunk_root->node);
+	if (!test_bit(EXTENT_BUFFER_UPTODATE, &chunk_root->node->bflags)) {
+		printk(KERN_WARNING "btrfs: failed to read chunk root on %s\n",
+		       sb->s_id);
+		goto fail_chunk_root;
+	}
 	btrfs_set_root_node(&chunk_root->root_item, chunk_root->node);
 	chunk_root->commit_root = btrfs_root_node(chunk_root);
 
@@ -1810,6 +1815,11 @@
 					  blocksize, generation);
 	if (!tree_root->node)
 		goto fail_chunk_root;
+	if (!test_bit(EXTENT_BUFFER_UPTODATE, &tree_root->node->bflags)) {
+		printk(KERN_WARNING "btrfs: failed to read tree root on %s\n",
+		       sb->s_id);
+		goto fail_tree_root;
+	}
 	btrfs_set_root_node(&tree_root->root_item, tree_root->node);
 	tree_root->commit_root = btrfs_root_node(tree_root);