Btrfs: Add drop inode func to avoid data=ordered deadlock

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

fs/btrfs/ctree.h

@@ -1144,6 +1144,7 @@ int btrfs_check_free_space(struct btrfs_root *root, u64 num_required,
 int btrfs_page_mkwrite(struct vm_area_struct *vma, struct page *page);
 int btrfs_readpage(struct file *file, struct page *page);
 void btrfs_delete_inode(struct inode *inode);
+void btrfs_drop_inode(struct inode *inode);
 void btrfs_read_locked_inode(struct inode *inode);
 int btrfs_write_inode(struct inode *inode, int wait);
 void btrfs_dirty_inode(struct inode *inode);

fs/btrfs/inode.c

@@ -990,6 +990,25 @@ out:
 fail:
 	return err;
 }
+
+void btrfs_drop_inode(struct inode *inode)
+{
+	struct btrfs_trans_handle *trans;
+	struct btrfs_root *root = BTRFS_I(inode)->root;
+
+	if (!BTRFS_I(inode)->ordered_trans) {
+		generic_drop_inode(inode);
+		return;
+	}
+	/* nasty, but it prevents a deadlock with data=ordered by preventing
+	 * a commit until after this inode is done
+	 */
+	trans = btrfs_start_transaction(root, 1);
+	generic_drop_inode(inode);
+	/* note, the inode is now untouchable */
+	btrfs_end_transaction(trans, root);
+}
+
 void btrfs_delete_inode(struct inode *inode)
 {
 	struct btrfs_trans_handle *trans;

fs/btrfs/super.c

@@ -425,6 +425,7 @@ static struct file_system_type btrfs_fs_type = {
 
 static struct super_operations btrfs_super_ops = {
 	.delete_inode	= btrfs_delete_inode,
+	.drop_inode	= btrfs_drop_inode,
 	.put_super	= btrfs_put_super,
 	.read_inode	= btrfs_read_locked_inode,
 	.write_super	= btrfs_write_super,