Index: geom/geom_io.c
===================================================================
--- geom/geom_io.c	(revision 195187)
+++ geom/geom_io.c	(working copy)
@@ -480,14 +480,6 @@ g_io_deliver(struct bio *bp, int error)
 	KASSERT(bp != NULL, ("NULL bp in g_io_deliver"));
 	pp = bp->bio_to;
 	KASSERT(pp != NULL, ("NULL bio_to in g_io_deliver"));
-#ifdef DIAGNOSTIC
-	KASSERT(bp->bio_caller1 == bp->_bio_caller1,
-	    ("bio_caller1 used by the provider %s", pp->name));
-	KASSERT(bp->bio_caller2 == bp->_bio_caller2,
-	    ("bio_caller2 used by the provider %s", pp->name));
-	KASSERT(bp->bio_cflags == bp->_bio_cflags,
-	    ("bio_cflags used by the provider %s", pp->name));
-#endif
 	cp = bp->bio_from;
 	if (cp == NULL) {
 		bp->bio_error = error;
@@ -496,6 +488,21 @@ g_io_deliver(struct bio *bp, int error)
 	}
 	KASSERT(cp != NULL, ("NULL bio_from in g_io_deliver"));
 	KASSERT(cp->geom != NULL, ("NULL bio_from->geom in g_io_deliver"));
+#ifdef DIAGNOSTIC
+	/*
+	 * Some classes - GJournal in particular - can modify bio's
+	 * private fields while the bio is in transit; G_GEOM_VOLATILE_BIO
+	 * flag means it's an expected behaviour for that particular geom.
+	 */
+	if ((cp->geom->flags & G_GEOM_VOLATILE_BIO) == 0) {
+		KASSERT(bp->bio_caller1 == bp->_bio_caller1,
+		    ("bio_caller1 used by the provider %s", pp->name));
+		KASSERT(bp->bio_caller2 == bp->_bio_caller2,
+		    ("bio_caller2 used by the provider %s", pp->name));
+		KASSERT(bp->bio_cflags == bp->_bio_cflags,
+		    ("bio_cflags used by the provider %s", pp->name));
+	}
+#endif
 	KASSERT(bp->bio_completed >= 0, ("bio_completed can't be less than 0"));
 	KASSERT(bp->bio_completed <= bp->bio_length,
 	    ("bio_completed can't be greater than bio_length"));
Index: geom/journal/g_journal.c
===================================================================
--- geom/journal/g_journal.c	(revision 195187)
+++ geom/journal/g_journal.c	(working copy)
@@ -2292,6 +2292,7 @@ g_journal_create(struct g_class *mp, struct g_prov
 		gp->orphan = g_journal_orphan;
 		gp->access = g_journal_access;
 		gp->softc = sc;
+		gp->flags |= G_GEOM_VOLATILE_BIO;
 		sc->sc_geom = gp;
 
 		mtx_init(&sc->sc_mtx, "gjournal", NULL, MTX_DEF);
Index: geom/geom.h
===================================================================
--- geom/geom.h	(revision 195187)
+++ geom/geom.h	(working copy)
@@ -134,6 +134,7 @@ struct g_geom {
 	void			*softc;
 	unsigned		flags;
 #define	G_GEOM_WITHER		1
+#define	G_GEOM_VOLATILE_BIO	2
 };
 
 /*