[PATCH 5.4 CANDIDATE 22/26] xfs: trylock underlying buffer on dquot flush

[Chandan Babu R <chandan.babu@oracle.com>]

From: Brian Foster <bfoster@redhat.com>

commit 8d3d7e2b35ea7d91d6e085c93b5efecfb0fba307 upstream.

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>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Chandan Babu R <chandan.babu@oracle.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 55c73f012762..9596b86e7de9 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;
 
@@ -1176,7 +1176,7 @@ 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;
 
 	spin_lock(&lip->li_ailp->ail_lock);
 out_unlock:
diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index fe93e044d81b..ef2faee96909 100644
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -121,12 +121,11 @@ xfs_qm_dqpurge(
 {
 	struct xfs_mount	*mp = dqp->q_mount;
 	struct xfs_quotainfo	*qi = mp->m_quotainfo;
+	int			error = -EAGAIN;
 
 	xfs_dqlock(dqp);
-	if ((dqp->dq_flags & XFS_DQ_FREEING) || dqp->q_nrefs != 0) {
-		xfs_dqunlock(dqp);
-		return -EAGAIN;
-	}
+	if ((dqp->dq_flags & XFS_DQ_FREEING) || dqp->q_nrefs != 0)
+		goto out_unlock;
 
 	dqp->dq_flags |= XFS_DQ_FREEING;
 
@@ -139,7 +138,6 @@ xfs_qm_dqpurge(
 	 */
 	if (XFS_DQ_IS_DIRTY(dqp)) {
 		struct xfs_buf	*bp = NULL;
-		int		error;
 
 		/*
 		 * We don't care about getting disk errors here. We need
@@ -149,6 +147,8 @@ xfs_qm_dqpurge(
 		if (!error) {
 			error = xfs_bwrite(bp);
 			xfs_buf_relse(bp);
+		} else if (error == -EAGAIN) {
+			goto out_unlock;
 		}
 		xfs_dqflock(dqp);
 	}
@@ -174,6 +174,10 @@ xfs_qm_dqpurge(
 
 	xfs_qm_dqdestroy(dqp);
 	return 0;
+
+out_unlock:
+	xfs_dqunlock(dqp);
+	return error;
 }
 
 /*
-- 
2.35.1