- Fix the issue with read access count modification on RAID-5 plexes properly.

If the access counts were not increased and decreased in equal numbers by
  gvinum consumers, the read access count would be inconsistent with the write
  access count. Instead, modify the read access count with the write access
  count directly to prevent any inconsistencies.

Approved by:	re (kib)

sys/geom/vinum/geom_vinum.c

@@ -133,10 +133,12 @@ gv_access(struct g_provider *pp, int dr, int dw, int de)
 	error = ENXIO;
 	gp = pp->geom;
 	sc = gp->softc;
-	if (dw > 0 && dr == 0)
-		dr = 1;
-	else if (dw < 0 && dr == 0)
-		dr = -1;
+	/*
+	 * We want to modify the read count with the write count in case we have
+	 * plexes in a RAID-5 organization.
+	 */
+	dr += dw;
+
 	LIST_FOREACH(d, &sc->drives, drive) {
 		if (d->consumer == NULL)
 			continue;