Index: sys/dev/nvme/nvme_private.h
===================================================================
--- sys/dev/nvme/nvme_private.h
+++ sys/dev/nvme/nvme_private.h
@@ -215,6 +215,7 @@
 	boolean_t		is_enabled;
 
 	struct mtx		lock __aligned(CACHE_LINE_SIZE);
+	struct mtx		complete_lock __aligned(CACHE_LINE_SIZE);
 
 } __aligned(CACHE_LINE_SIZE);
 
Index: sys/dev/nvme/nvme_qpair.c
===================================================================
--- sys/dev/nvme/nvme_qpair.c
+++ sys/dev/nvme/nvme_qpair.c
@@ -541,6 +541,8 @@
 	if (!qpair->is_enabled)
 		return (false);
 
+	mtx_lock(&qpair->complete_lock);
+
 	/*
 	 * A panic can stop the CPU this routine is running on at any point.  If
 	 * we're called during a panic, complete the sq_head wrap protocol for
@@ -625,6 +627,7 @@
 		nvme_mmio_write_4(qpair->ctrlr, doorbell[qpair->id].cq_hdbl,
 		    qpair->cq_head);
 	}
+	mtx_unlock(&qpair->complete_lock);
 	return (done != 0);
 }
 
@@ -676,6 +679,7 @@
 	}
 
 	mtx_init(&qpair->lock, "nvme qpair lock", NULL, MTX_DEF);
+	mtx_init(&qpair->complete_lock, "nvme qpair process completions lock", NULL, MTX_DEF);
 
 	/* Note: NVMe PRP format is restricted to 4-byte alignment. */
 	err = bus_dma_tag_create(bus_get_dma_tag(ctrlr->dev),
@@ -796,6 +800,9 @@
 	if (mtx_initialized(&qpair->lock))
 		mtx_destroy(&qpair->lock);
 
+	if (mtx_initialized(&qpair->complete_lock))
+		mtx_destroy(&qpair->complete_lock);
+
 	if (qpair->res)
 		bus_release_resource(qpair->ctrlr->dev, SYS_RES_IRQ,
 		    rman_get_rid(qpair->res), qpair->res);
@@ -890,6 +897,9 @@
 	uint32_t		csts;
 	uint8_t			cfs;
 
+	/* XXX debugging XXX */
+	nvme_printf(ctrlr, "nvme_timeout\n");
+
 	/*
 	 * Read csts to get value of cfs - controller fatal status.
 	 * If no fatal status, try to call the completion routine, and