linux-kernel - Re: xfs: cancel dfops on xfs_defer

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Date:   Tue, 7 Aug 2018 08:10:29 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Brian Foster <bfoster@...hat.com>
Cc:     Colin Ian King <colin.king@...onical.com>,
        linux-xfs@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: xfs: cancel dfops on xfs_defer_finish() error

On Tue, Aug 07, 2018 at 10:37:21AM -0400, Brian Foster wrote:
> On Tue, Aug 07, 2018 at 03:14:07PM +0100, Colin Ian King wrote:
> > Hi,
> > 
> > Recent commit 82ff27bc52a88cb5cc400bfa64e210d3ec8dfebd ("xfs: automatic
> > dfops buffer relogging") removed the assignment of variable error:
> > 
> > -       error = xfs_defer_bjoin(tp->t_dfops, bp);
> >         if (error) {
> >                 xfs_trans_bhold_release(tp, bp);
> >                 xfs_trans_brelse(tp, bp);
> > 
> 
> Hmm, I _think_ we can just drop these error checks now that this
> pre-finish error state is non-existent, something like the appended diff
> (with additional cleanups). E.g., if the buffer is held in the
> transaction then the bjoin is implicit. If the finish fails, then the
> state is essentially unchanged by the relogging patch.
> 
> That said, the error handling is a bit tricky here. Darrick, I think you
> reworked this recently.. thoughts?
> 
> Brian
> 
> --- 8< ---
> 
> diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c
> index 70a76ac41f01..2106c4142ecd 100644
> --- a/fs/xfs/xfs_dquot.c
> +++ b/fs/xfs/xfs_dquot.c
> @@ -311,7 +311,7 @@ xfs_dquot_disk_alloc(
>  			XFS_DQUOT_CLUSTER_SIZE_FSB, XFS_BMAPI_METADATA,
>  			XFS_QM_DQALLOC_SPACE_RES(mp), &map, &nmaps);
>  	if (error)
> -		goto error0;
> +		return error;
>  	ASSERT(map.br_blockcount == XFS_DQUOT_CLUSTER_SIZE_FSB);
>  	ASSERT(nmaps == 1);
>  	ASSERT((map.br_startblock != DELAYSTARTBLOCK) &&
> @@ -326,8 +326,8 @@ xfs_dquot_disk_alloc(
>  	bp = xfs_trans_get_buf(tp, mp->m_ddev_targp, dqp->q_blkno,
>  			mp->m_quotainfo->qi_dqchunklen, 0);
>  	if (!bp) {
> -		error = -ENOMEM;
> -		goto error1;
> +		xfs_defer_cancel(tp);
> +		return -ENOMEM;

The only caller of xfs_dquot_disk_alloc checks the return value and
xfs_trans_cancels the transaction, which should take care of calling
xfs_defer_cancel, right?

--D

>  	}
>  	bp->b_ops = &xfs_dquot_buf_ops;
>  
> @@ -349,10 +349,8 @@ xfs_dquot_disk_alloc(
>  	 * the buffer locked across the _defer_finish call.  We can now do
>  	 * this correctly with xfs_defer_bjoin.
>  	 *
> -	 * Above, we allocated a disk block for the dquot information and
> -	 * used get_buf to initialize the dquot.  If the _defer_bjoin fails,
> -	 * the buffer is still locked to *tpp, so we must _bhold_release and
> -	 * then _trans_brelse the buffer.  If the _defer_finish fails, the old
> +	 * Above, we allocated a disk block for the dquot information and used
> +	 * get_buf to initialize the dquot. If the _defer_finish fails, the old
>  	 * transaction is gone but the new buffer is not joined or held to any
>  	 * transaction, so we must _buf_relse it.
>  	 *
> @@ -362,24 +360,14 @@ xfs_dquot_disk_alloc(
>  	 * manually or by committing the transaction.
>  	 */
>  	xfs_trans_bhold(tp, bp);
> -	if (error) {
> -		xfs_trans_bhold_release(tp, bp);
> -		xfs_trans_brelse(tp, bp);
> -		goto error1;
> -	}
>  	error = xfs_defer_finish(tpp);
>  	tp = *tpp;
>  	if (error) {
>  		xfs_buf_relse(bp);
> -		goto error0;
> +		return error;
>  	}
>  	*bpp = bp;
>  	return 0;
> -
> -error1:
> -	xfs_defer_cancel(tp);
> -error0:
> -	return error;
>  }
>  
>  /*
> --
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