Index: sys/dev/random/random_harvestq.c
===================================================================
--- sys/dev/random/random_harvestq.c
+++ sys/dev/random/random_harvestq.c
@@ -523,6 +523,12 @@
 	u_int ring_in;
 
 	KASSERT(origin >= RANDOM_START && origin < ENTROPYSOURCE, ("%s: origin %d invalid\n", __func__, origin));
+
+	/* Do a very dirty check to avoid taking lock if not necessary */
+	if (((harvest_context.hc_entropy_ring.in + 1) % RANDOM_RING_MAX)
+	    == harvest_context.hc_entropy_ring.out)
+		return;
+
 	RANDOM_HARVEST_LOCK();
 	ring_in = (harvest_context.hc_entropy_ring.in + 1)%RANDOM_RING_MAX;
 	if (ring_in != harvest_context.hc_entropy_ring.out) {