Re: [PATCH 1/2] xfs: write unmount record for ro mounts

[Brian Foster <bfoster@redhat.com>]

On Thu, Mar 09, 2017 at 02:15:01PM -0600, Eric Sandeen wrote:
> There are dueling comments in the xfs code about intent
> for log writes when unmounting a readonly filesystem.
> 
> In xfs_mountfs, we see the intent:
> 
> /*
>  * Now the log is fully replayed, we can transition to full read-only
>  * mode for read-only mounts. This will sync all the metadata and clean
>  * the log so that the recovery we just performed does not have to be
>  * replayed again on the next mount.
>  */
> 
> and it calls xfs_quiesce_attr(), but by the time we get to 
> xfs_log_unmount_write(), it returns early for a RDONLY mount:
> 
>  * Don't write out unmount record on read-only mounts.
> 
> Because of this, sequential ro mounts of a filesystem with
> a dirty log will replay the log each time, which seems odd.
> 
> Fix this by writing an unmount record even for RO mounts, as long
> as norecovery wasn't specified (don't write a clean log record
> if a dirty log may still be there!) and the log device is
> writable.
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

> 
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index b1469f0..62176b8 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -801,11 +801,14 @@
>  	int		 error;
>  
>  	/*
> -	 * Don't write out unmount record on read-only mounts.
> +	 * Don't write out unmount record on norecovery mounts or ro devices.
>  	 * Or, if we are doing a forced umount (typically because of IO errors).
>  	 */
> -	if (mp->m_flags & XFS_MOUNT_RDONLY)
> +	if (mp->m_flags & XFS_MOUNT_NORECOVERY ||
> +	    xfs_readonly_buftarg(log->l_mp->m_logdev_targp)) {
> +		ASSERT(mp->m_flags & XFS_MOUNT_RDONLY);
>  		return 0;
> +	}
>  
>  	error = _xfs_log_force(mp, XFS_LOG_SYNC, NULL);
>  	ASSERT(error || !(XLOG_FORCED_SHUTDOWN(log)));
> 
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