btrfs: Add graceful handling of V0 extents

Following the removal of the v0 handling code let's be courteous and
print an error message when such extents are handled. In the cases
where we have a transaction just abort it, otherwise just call
btrfs_handle_fs_error. Both cases result in the FS being re-mounted RO.

In case the error handling would be too intrusive, leave the BUG_ON in
place, like extent_data_ref_count, other proper handling would catch
that earlier.

Signed-off-by: Nikolay Borisov <[e-mail]>
Reviewed-by: David Sterba <[e-mail]>
Signed-off-by: David Sterba <[e-mail]>

fs/btrfs/ctree.h

···
 #define ASSERT(expr)	((void)0)
 #endif
 
+__cold
+static inline void btrfs_print_v0_err(struct btrfs_fs_info *fs_info)
+{
+	btrfs_err(fs_info,
+"Unsupported V0 extent filesystem detected. Aborting. Please re-create your filesystem with a newer kernel");
+}
+
 __printf(5, 6)
 __cold
 void __btrfs_handle_fs_error(struct btrfs_fs_info *fs_info, const char *function,

fs/btrfs/extent-tree.c

···
 			num_refs = btrfs_extent_refs(leaf, ei);
 			extent_flags = btrfs_extent_flags(leaf, ei);
 		} else {
-			BUG();
+			ret = -EINVAL;
+			btrfs_print_v0_err(fs_info);
+			if (trans)
+				btrfs_abort_transaction(trans, ret);
+			else
+				btrfs_handle_fs_error(fs_info, ret, NULL);
+
+			goto out_free;
 		}
+
 		BUG_ON(num_refs == 0);
 	} else {
 		num_refs = 0;
···
 		ref2 = btrfs_item_ptr(leaf, path->slots[0],
 				      struct btrfs_shared_data_ref);
 		num_refs = btrfs_shared_data_ref_count(leaf, ref2);
+	} else if (key.type == BTRFS_EXTENT_REF_V0_KEY) {
+		btrfs_print_v0_err(trans->fs_info);
+		btrfs_abort_transaction(trans, -EINVAL);
+		return -EINVAL;
 	} else {
 		BUG();
 	}
···
 
 	leaf = path->nodes[0];
 	btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+
+	BUG_ON(key.type == BTRFS_EXTENT_REF_V0_KEY);
 	if (iref) {
 		/*
 		 * If type is invalid, we should have bailed out earlier than
···
 
 	leaf = path->nodes[0];
 	item_size = btrfs_item_size_nr(leaf, path->slots[0]);
-	BUG_ON(item_size < sizeof(*ei));
+	if (item_size < sizeof(*ei)) {
+		err = -EINVAL;
+		btrfs_print_v0_err(fs_info);
+		btrfs_abort_transaction(trans, err);
+		goto out;
+	}
 
 	ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
 	flags = btrfs_extent_flags(leaf, ei);
···
 
 	leaf = path->nodes[0];
 	item_size = btrfs_item_size_nr(leaf, path->slots[0]);
-	BUG_ON(item_size < sizeof(*ei));
+
+	if (item_size < sizeof(*ei)) {
+		err = -EINVAL;
+		btrfs_print_v0_err(fs_info);
+		btrfs_abort_transaction(trans, err);
+		goto out;
+	}
+
 	ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
 	__run_delayed_extent_op(extent_op, leaf, ei);
 
···
 
 	leaf = path->nodes[0];
 	item_size = btrfs_item_size_nr(leaf, extent_slot);
-	BUG_ON(item_size < sizeof(*ei));
+	if (item_size < sizeof(*ei)) {
+		ret = -EINVAL;
+		btrfs_print_v0_err(info);
+		btrfs_abort_transaction(trans, ret);
+		goto out;
+	}
 	ei = btrfs_item_ptr(leaf, extent_slot,
 			    struct btrfs_extent_item);
 	if (owner_objectid < BTRFS_FIRST_FREE_OBJECTID &&

fs/btrfs/print-tree.c

···
 	u64 offset;
 	int ref_index = 0;
 
-	if (item_size < sizeof(*ei))
-		BUG();
+	if (item_size < sizeof(*ei)) {
+		btrfs_print_v0_err(eb->fs_info);
+		btrfs_handle_fs_error(eb->fs_info, -EINVAL, NULL);
+	}
 
 	ei = btrfs_item_ptr(eb, slot, struct btrfs_extent_item);
 	flags = btrfs_extent_flags(eb, ei);
···
 			       btrfs_file_extent_ram_bytes(l, fi));
 			break;
 		case BTRFS_EXTENT_REF_V0_KEY:
-			BUG();
+			btrfs_print_v0_err(fs_info);
+			btrfs_handle_fs_error(fs_info, -EINVAL, NULL);
 			break;
 		case BTRFS_BLOCK_GROUP_ITEM_KEY:
 			bi = btrfs_item_ptr(l, i,

fs/btrfs/relocation.c

···
 	btrfs_item_key_to_cpu(leaf, &key, slot);
 
 	item_size = btrfs_item_size_nr(leaf, slot);
+	if (item_size < sizeof(*ei)) {
+		btrfs_print_v0_err(leaf->fs_info);
+		btrfs_handle_fs_error(leaf->fs_info, -EINVAL, NULL);
+		return 1;
+	}
 	ei = btrfs_item_ptr(leaf, slot, struct btrfs_extent_item);
 	WARN_ON(!(btrfs_extent_flags(leaf, ei) &
 		  BTRFS_EXTENT_FLAG_TREE_BLOCK));
···
 			goto next;
 		}
 
-		ASSERT(key.type != BTRFS_EXTENT_REF_V0_KEY);
 		if (key.type == BTRFS_SHARED_BLOCK_REF_KEY) {
 			if (key.objectid == key.offset) {
 				/*
···
 			edge->node[UPPER] = upper;
 
 			goto next;
+		} else if (key.type == BTRFS_EXTENT_REF_V0_KEY) {
+			err = -EINVAL;
+			btrfs_print_v0_err(rc->extent_root->fs_info);
+			btrfs_handle_fs_error(rc->extent_root->fs_info, err,
+					      NULL);
+			goto out;
 		} else if (key.type != BTRFS_TREE_BLOCK_REF_KEY) {
 			goto next;
 		}
···
 			level = (int)extent_key->offset;
 		}
 		generation = btrfs_extent_generation(eb, ei);
+	} else if (item_size == sizeof(struct btrfs_extent_item_v0)) {
+		btrfs_print_v0_err(eb->fs_info);
+		btrfs_handle_fs_error(eb->fs_info, -EINVAL, NULL);
+		return -EINVAL;
 	} else {
 		BUG();
 	}
···
 		if (key.objectid != extent_key->objectid)
 			break;
 
-		BUG_ON(key.type == BTRFS_EXTENT_REF_V0_KEY);
 		if (key.type == BTRFS_SHARED_DATA_REF_KEY) {
 			ret = __add_tree_block(rc, key.offset, blocksize,
 					       blocks);
···
 					      struct btrfs_extent_data_ref);
 			ret = find_data_references(rc, extent_key,
 						   eb, dref, blocks);
+		} else if (key.type == BTRFS_EXTENT_REF_V0_KEY) {
+			btrfs_print_v0_err(eb->fs_info);
+			btrfs_handle_fs_error(eb->fs_info, -EINVAL, NULL);
+			ret = -EINVAL;
 		} else {
 			ret = 0;
 		}
···
 			flags = btrfs_extent_flags(path->nodes[0], ei);
 			ret = check_extent_flags(flags);
 			BUG_ON(ret);
-
+		} else if (item_size == sizeof(struct btrfs_extent_item_v0)) {
+			err = -EINVAL;
+			btrfs_print_v0_err(trans->fs_info);
+			btrfs_abort_transaction(trans, err);
+			break;
 		} else {
 			BUG();
 		}