Re: [PATCH 1/2] xfs: refactor xfs_file_fsync

[Brian Foster <bfoster@redhat.com>]

On Mon, Jan 11, 2021 at 05:15:43PM +0100, Christoph Hellwig wrote:
> Factor out the log syncing logic into two helpers to make the code easier
> to read and more maintainable.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---

Looks fine, though it might be nice to find some commonality with
xfs_log_force_inode():

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

>  fs/xfs/xfs_file.c | 81 +++++++++++++++++++++++++++++------------------
>  1 file changed, 50 insertions(+), 31 deletions(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 5b0f93f738372d..414d856e2e755a 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -118,6 +118,54 @@ xfs_dir_fsync(
>  	return xfs_log_force_inode(ip);
>  }
>  
> +static xfs_lsn_t
> +xfs_fsync_lsn(
> +	struct xfs_inode	*ip,
> +	bool			datasync)
> +{
> +	if (!xfs_ipincount(ip))
> +		return 0;
> +	if (datasync && !(ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP))
> +		return 0;
> +	return ip->i_itemp->ili_last_lsn;
> +}
> +
> +/*
> + * All metadata updates are logged, which means that we just have to flush the
> + * log up to the latest LSN that touched the inode.
> + *
> + * If we have concurrent fsync/fdatasync() calls, we need them to all block on
> + * the log force before we clear the ili_fsync_fields field. This ensures that
> + * we don't get a racing sync operation that does not wait for the metadata to
> + * hit the journal before returning.  If we race with clearing ili_fsync_fields,
> + * then all that will happen is the log force will do nothing as the lsn will
> + * already be on disk.  We can't race with setting ili_fsync_fields because that
> + * is done under XFS_ILOCK_EXCL, and that can't happen because we hold the lock
> + * shared until after the ili_fsync_fields is cleared.
> + */
> +static  int
> +xfs_fsync_flush_log(
> +	struct xfs_inode	*ip,
> +	bool			datasync,
> +	int			*log_flushed)
> +{
> +	int			error = 0;
> +	xfs_lsn_t		lsn;
> +
> +	xfs_ilock(ip, XFS_ILOCK_SHARED);
> +	lsn = xfs_fsync_lsn(ip, datasync);
> +	if (lsn) {
> +		error = xfs_log_force_lsn(ip->i_mount, lsn, XFS_LOG_SYNC,
> +					  log_flushed);
> +
> +		spin_lock(&ip->i_itemp->ili_lock);
> +		ip->i_itemp->ili_fsync_fields = 0;
> +		spin_unlock(&ip->i_itemp->ili_lock);
> +	}
> +	xfs_iunlock(ip, XFS_ILOCK_SHARED);
> +	return error;
> +}
> +
>  STATIC int
>  xfs_file_fsync(
>  	struct file		*file,
> @@ -125,13 +173,10 @@ xfs_file_fsync(
>  	loff_t			end,
>  	int			datasync)
>  {
> -	struct inode		*inode = file->f_mapping->host;
> -	struct xfs_inode	*ip = XFS_I(inode);
> -	struct xfs_inode_log_item *iip = ip->i_itemp;
> +	struct xfs_inode	*ip = XFS_I(file->f_mapping->host);
>  	struct xfs_mount	*mp = ip->i_mount;
>  	int			error = 0;
>  	int			log_flushed = 0;
> -	xfs_lsn_t		lsn = 0;
>  
>  	trace_xfs_file_fsync(ip);
>  
> @@ -155,33 +200,7 @@ xfs_file_fsync(
>  	else if (mp->m_logdev_targp != mp->m_ddev_targp)
>  		xfs_blkdev_issue_flush(mp->m_ddev_targp);
>  
> -	/*
> -	 * All metadata updates are logged, which means that we just have to
> -	 * flush the log up to the latest LSN that touched the inode. If we have
> -	 * concurrent fsync/fdatasync() calls, we need them to all block on the
> -	 * log force before we clear the ili_fsync_fields field. This ensures
> -	 * that we don't get a racing sync operation that does not wait for the
> -	 * metadata to hit the journal before returning. If we race with
> -	 * clearing the ili_fsync_fields, then all that will happen is the log
> -	 * force will do nothing as the lsn will already be on disk. We can't
> -	 * race with setting ili_fsync_fields because that is done under
> -	 * XFS_ILOCK_EXCL, and that can't happen because we hold the lock shared
> -	 * until after the ili_fsync_fields is cleared.
> -	 */
> -	xfs_ilock(ip, XFS_ILOCK_SHARED);
> -	if (xfs_ipincount(ip)) {
> -		if (!datasync ||
> -		    (iip->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP))
> -			lsn = iip->ili_last_lsn;
> -	}
> -
> -	if (lsn) {
> -		error = xfs_log_force_lsn(mp, lsn, XFS_LOG_SYNC, &log_flushed);
> -		spin_lock(&iip->ili_lock);
> -		iip->ili_fsync_fields = 0;
> -		spin_unlock(&iip->ili_lock);
> -	}
> -	xfs_iunlock(ip, XFS_ILOCK_SHARED);
> +	error = xfs_fsync_flush_log(ip, datasync, &log_flushed);
>  
>  	/*
>  	 * If we only have a single device, and the log force about was
> -- 
> 2.29.2
>