@BABOLO modify 2005-04-26 Original http://www.ambrisko.com/doug/ata/
--- sys/kern/subr_disk.c
+++ sys/kern/subr_disk.c
@@ -195,8 +195,9 @@
 	
 	error = dsopen(dev, devtype, dp->d_dsflags, &dp->d_slice, &dp->d_label);
 
-	if (!dsisopen(dp->d_slice)) 
-		dp->d_devsw->d_close(pdev, oflags, devtype, p);
+	if (!dsisopen(dp->d_slice))
+		if(dp->d_devsw)
+			dp->d_devsw->d_close(pdev, oflags, devtype, p);
 out:	
 	dp->d_flags &= ~DISKFLAG_LOCK;
 	if (dp->d_flags & DISKFLAG_WANTED) {
--- sys/kern/subr_diskslice.c
+++ sys/kern/subr_diskslice.c
@@ -321,7 +321,7 @@
 	struct diskslice *sp;
 	struct diskslices *ssp;
 
-	for (slice = 0, ssp = *sspp; slice < ssp->dss_nslices; slice++) {
+	for (slice = 0, ssp = *sspp; ssp && slice < ssp->dss_nslices; slice++) {
 		sp = &ssp->dss_slices[slice];
 		free_ds_label(ssp, slice);
 	}