xfs: don't run the sync work if the filesystem is read-only

If the filesystem is mounted or remounted read-only, stop the sync
worker that tries to flush or cover the log if the filesystem is
dirty. It's read-only, so it isn't dirty. Restart it on a remount,rw
as necessary. This avoids the need for RO checks in the work.

Similarly, stop the sync work when the filesystem is frozen, and
start it again when the filesysetm is thawed. This avoids the need
for special freeze checks in the work.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>

fs/xfs/xfs_super.c

@@ -1200,6 +1200,7 @@ xfs_fs_remount(
 		 * value if it is non-zero, otherwise go with the default.
 		 */
 		xfs_restore_resvblks(mp);
+		xfs_syncd_queue_sync(mp);
 	}
 
 	/* rw -> ro */
@@ -1245,6 +1246,7 @@ xfs_fs_unfreeze(
 	struct xfs_mount	*mp = XFS_M(sb);
 
 	xfs_restore_resvblks(mp);
+	xfs_syncd_queue_sync(mp);
 	return 0;
 }
 

fs/xfs/xfs_sync.c

@@ -323,6 +323,9 @@ xfs_quiesce_data(
  * Second stage of a quiesce. The data is already synced, now we have to take
  * care of the metadata. New transactions are already blocked, so we need to
  * wait for any remaining transactions to drain out before proceeding.
+ *
+ * Note: this stops background sync work - the callers must ensure it is started
+ * again when appropriate.
  */
 void
 xfs_quiesce_attr(
@@ -341,6 +344,9 @@ xfs_quiesce_attr(
 	/* flush all pending changes from the AIL */
 	xfs_ail_push_all_sync(mp->m_ail);
 
+	/* stop background sync work */
+	cancel_delayed_work_sync(&mp->m_sync_work);
+
 	/*
 	 * Just warn here till VFS can correctly support
 	 * read-only remount without racing.
@@ -379,9 +385,8 @@ xfs_syncd_queue_sync(
 }
 
 /*
- * Every sync period we need to unpin all items in the AIL and push them to
- * disk. If there is nothing dirty, then we might need to cover the log to
- * indicate that the filesystem is idle and not frozen.
+ * Every sync period we need to push dirty metadata and try to cover the log
+ * to indicate the filesystem is idle and not frozen.
  */
 void
 xfs_sync_worker(
@@ -391,7 +396,6 @@ xfs_sync_worker(
 					struct xfs_mount, m_sync_work);
 	int		error;
 
-	if (!(mp->m_flags & XFS_MOUNT_RDONLY)) {
 	/* dgc: errors ignored here */
 	if (mp->m_super->s_writers.frozen == SB_UNFROZEN &&
 	    xfs_log_need_covered(mp))
@@ -401,7 +405,6 @@ xfs_sync_worker(
 
 	/* start pushing all the metadata that is currently dirty */
 	xfs_ail_push_all(mp->m_ail);
-	}
 
 	/* queue us up again */
 	xfs_syncd_queue_sync(mp);