diff --git a/sys/kern/kern_dmsg.c b/sys/kern/kern_dmsg.c
--- a/sys/kern/kern_dmsg.c
+++ b/sys/kern/kern_dmsg.c
@@ -1759,6 +1759,16 @@
 	KKASSERT((state->flags & KDMSG_STATE_SUBINSERTED) == 0);
 	KKASSERT(TAILQ_EMPTY(&state->subq));
 
+	/*
+	 * Free any per-state auxiliary allocation (e.g. dios_open / dios_io
+	 * from subr_diskiocom.c) so repeated OPEN/READ-WITH-DELETE cycles
+	 * do not leak M_DEVBUF.
+	 */
+	if (state->any.any != NULL) {
+		kfree(state->any.any, iocom->mmsg);
+		state->any.any = NULL;
+	}
+
 	if (state != &state->iocom->state0)
 		kfree(state, iocom->mmsg);
 }