zfsctl: No need to sync ctldir inodes

There's no metadata to write to disk for ctldir inodes. So we check if
a inode belongs to the ctldir in zpl_commit_metadata, and returns
immediately if it is.

Signed-off-by: Andrey Vesnovaty <andrey.vesnovaty@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #2797

module/zfs/zpl_export.c

@@ -152,6 +152,9 @@ zpl_commit_metadata(struct inode *inode)
 	fstrans_cookie_t cookie;
 	int error;
 
+	if (zfsctl_is_node(inode))
+		return (0);
+
 	crhold(cr);
 	cookie = spl_fstrans_mark();
 	error = -zfs_fsync(inode, 0, cr);