quoted

+static struct netc_cbdr *netc_select_cbdr(struct ntmp_user *user)
+{
+	int cpu, i;
+
+	for (i = 0; i < user->cbdr_num; i++) {
+		if (spin_is_locked(&user->ring[i].ring_lock))
+			continue;
+
+		return &user->ring[i];
+	}
+
+	/* If all the command BDRs are busy now, we select
+	 * one of them, but need to wait for a while to use.
+	 */
+	cpu = smp_processor_id();
+
+	return &user->ring[cpu % user->cbdr_num];
+}
+

Can this trigger a preemption warning? netc_select_cbdr() is called from
netc_xmit_ntmp_cmd() before spin_lock_bh() is acquired, and the callers
(ntmp_maft_add_entry, ntmp_fdbt_add_entry, etc.) run in process context
with preemption enabled.

Using smp_processor_id() in preemptible code triggers a
"BUG: using smp_processor_id() in preemptible code" warning under
CONFIG_DEBUG_PREEMPT.

Since the CPU value here is only used as a hint for ring selection and not
for correctness, would raw_smp_processor_id() be more appropriate?

It seems to be a potential issue, raw_smp_processor_id() is more appropriate,
thanks.