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

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Date:   Tue, 7 Aug 2018 10:37:21 -0400
From:   Brian Foster <bfoster@...hat.com>
To:     Colin Ian King <colin.king@...onical.com>
Cc:     darrick.wong@...cle.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 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;
 	}
 	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;
 }
 
 /*