[PATCH 1/1] xfs: fix buffer flushing during log unmount

[Christoph Hellwig]

> Whenever there is a mount/unmount failure - there is a chance of calling the
> callbacks functions once - transaction ail mount pointer is destroyed. So, it results
> in NULL pointer exception followed by hang. So, before unmount of the log - flush all
> the pending buffers.

>  void
>  xfs_log_unmount(xfs_mount_t *mp)
>  {
> +	int error = 0;
> +	/*
> +	 * Make sure all buffers have been flushed and completed before
> +	 * unmounting the log.
> +	 */
> +	error = xfs_flush_buftarg(mp->m_ddev_targp, 1);
> +	if (error)
> +		cmn_err(CE_WARN, "%d busy buffers during log unmount.", error);
> +	xfs_wait_buftarg(mp->m_ddev_targp);
> +	

We do exactly that sequence before the xfs_log_unmount_write call on
umount.  Care to explain what code in xfs_log_unmount_write would
require this to be called again?