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

[Brian Foster <bfoster@redhat.com>]

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;
 
 	spin_lock(&lip->li_ailp->ail_lock);
 out_unlock:
diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index de1d2c606c14..68c778d25c48 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;
 }
 
 /*
-- 
2.21.1