static void vmbus_wait_for_unload()

in channel_mgmt.c [796:871]

• 39 lines of code
• 6 McCabe index (conditional complexity)

static void vmbus_wait_for_unload(void)
{
	int cpu;
	void *page_addr;
	struct hv_message *msg;
	struct vmbus_channel_message_header *hdr;
	u32 message_type, i;

	/*
	 * CHANNELMSG_UNLOAD_RESPONSE is always delivered to the CPU which was
	 * used for initial contact or to CPU0 depending on host version. When
	 * we're crashing on a different CPU let's hope that IRQ handler on
	 * the cpu which receives CHANNELMSG_UNLOAD_RESPONSE is still
	 * functional and vmbus_unload_response() will complete
	 * vmbus_connection.unload_event. If not, the last thing we can do is
	 * read message pages for all CPUs directly.
	 *
	 * Wait up to 100 seconds since an Azure host must writeback any dirty
	 * data in its disk cache before the VMbus UNLOAD request will
	 * complete. This flushing has been empirically observed to take up
	 * to 50 seconds in cases with a lot of dirty data, so allow additional
	 * leeway and for inaccuracies in mdelay(). But eventually time out so
	 * that the panic path can't get hung forever in case the response
	 * message isn't seen.
	 */
	for (i = 1; i <= UNLOAD_WAIT_LOOPS; i++) {
		if (completion_done(&vmbus_connection.unload_event))
			goto completed;

		for_each_online_cpu(cpu) {
			struct hv_per_cpu_context *hv_cpu
				= per_cpu_ptr(hv_context.cpu_context, cpu);

			page_addr = hv_cpu->synic_message_page;
			msg = (struct hv_message *)page_addr
				+ VMBUS_MESSAGE_SINT;

			message_type = READ_ONCE(msg->header.message_type);
			if (message_type == HVMSG_NONE)
				continue;

			hdr = (struct vmbus_channel_message_header *)
				msg->u.payload;

			if (hdr->msgtype == CHANNELMSG_UNLOAD_RESPONSE)
				complete(&vmbus_connection.unload_event);

			vmbus_signal_eom(msg, message_type);
		}

		/*
		 * Give a notice periodically so someone watching the
		 * serial output won't think it is completely hung.
		 */
		if (!(i % UNLOAD_MSG_LOOPS))
			pr_notice("Waiting for VMBus UNLOAD to complete\n");

		mdelay(UNLOAD_DELAY_UNIT_MS);
	}
	pr_err("Continuing even though VMBus UNLOAD did not complete\n");

completed:
	/*
	 * We're crashing and already got the UNLOAD_RESPONSE, cleanup all
	 * maybe-pending messages on all CPUs to be able to receive new
	 * messages after we reconnect.
	 */
	for_each_online_cpu(cpu) {
		struct hv_per_cpu_context *hv_cpu
			= per_cpu_ptr(hv_context.cpu_context, cpu);

		page_addr = hv_cpu->synic_message_page;
		msg = (struct hv_message *)page_addr + VMBUS_MESSAGE_SINT;
		msg->header.message_type = HVMSG_NONE;
	}
}