Re: [PATCH 1/2] xfs: trylock underlying buffer on dquot flush

[Dave Chinner <david@fromorbit.com>]

On Thu, Mar 26, 2020 at 09:17:02AM -0400, Brian Foster wrote:
> A dquot flush currently blocks on the buffer lock for the underlying
> dquot buffer. In turn, this causes xfsaild to block rather than
> continue processing other items in the meantime. Update
> xfs_qm_dqflush() to trylock the buffer, similar to how inode buffers
> are handled, and return -EAGAIN if the lock fails. Fix up any
> callers that don't currently handle the error properly.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>
> ---
>  fs/xfs/xfs_dquot.c      |  6 +++---
>  fs/xfs/xfs_dquot_item.c |  3 ++-
>  fs/xfs/xfs_qm.c         | 14 +++++++++-----
>  3 files changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c
> index 711376ca269f..af2c8e5ceea0 100644
> --- a/fs/xfs/xfs_dquot.c
> +++ b/fs/xfs/xfs_dquot.c
> @@ -1105,8 +1105,8 @@ xfs_qm_dqflush(
>  	 * Get the buffer containing the on-disk dquot
>  	 */
>  	error = xfs_trans_read_buf(mp, NULL, mp->m_ddev_targp, dqp->q_blkno,
> -				   mp->m_quotainfo->qi_dqchunklen, 0, &bp,
> -				   &xfs_dquot_buf_ops);
> +				   mp->m_quotainfo->qi_dqchunklen, XBF_TRYLOCK,
> +				   &bp, &xfs_dquot_buf_ops);
>  	if (error)
>  		goto out_unlock;
>  
> @@ -1177,7 +1177,7 @@ xfs_qm_dqflush(
>  
>  out_unlock:
>  	xfs_dqfunlock(dqp);
> -	return -EIO;
> +	return error;
>  }
>  
>  /*
> diff --git a/fs/xfs/xfs_dquot_item.c b/fs/xfs/xfs_dquot_item.c
> index cf65e2e43c6e..baad1748d0d1 100644
> --- a/fs/xfs/xfs_dquot_item.c
> +++ b/fs/xfs/xfs_dquot_item.c
> @@ -189,7 +189,8 @@ xfs_qm_dquot_logitem_push(
>  		if (!xfs_buf_delwri_queue(bp, buffer_list))
>  			rval = XFS_ITEM_FLUSHING;
>  		xfs_buf_relse(bp);
> -	}
> +	} else if (error == -EAGAIN)
> +		rval = XFS_ITEM_LOCKED;

Doesn't xfs_inode_item_push() also have this problem in that it
doesn't handle -EAGAIN properly?

Also, we can get -EIO, -EFSCORRUPTED, etc here. They probably
shouldn't return XFS_ITEM_SUCCESS, either....

Otherwise seems OK.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com