Drivers: hv: vmbus: Teardown clockevent devices on module unload

Newly introduced clockevent devices made it impossible to unload hv_vmbus
module as clockevents_config_and_register() takes additional reverence to
the module. To make it possible again we do the following:
- avoid setting dev->owner for clockevent devices;
- implement hv_synic_clockevents_cleanup() doing clockevents_unbind_device();
- call it from vmbus_exit().

In theory hv_synic_clockevents_cleanup() can be merged with hv_synic_cleanup(),
however, we call hv_synic_cleanup() from smp_call_function_single() and this
doesn't work for clockevents_unbind_device() as it does such call on its own. I
opted for a separate function.

Signed-off-by: Vitaly Kuznetsov <[e-mail]>
Signed-off-by: K. Y. Srinivasan <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/hv/hv.c

···
 	dev->features = CLOCK_EVT_FEAT_ONESHOT;
 	dev->cpumask = cpumask_of(cpu);
 	dev->rating = 1000;
-	dev->owner = THIS_MODULE;
+	/*
+	 * Avoid settint dev->owner = THIS_MODULE deliberately as doing so will
+	 * result in clockevents_config_and_register() taking additional
+	 * references to the hv_vmbus module making it impossible to unload.
+	 */
 
 	dev->set_mode = hv_ce_setmode;
 	dev->set_next_event = hv_ce_set_next_event;
···
 }
 
 /*
+ * hv_synic_clockevents_cleanup - Cleanup clockevent devices
+ */
+void hv_synic_clockevents_cleanup(void)
+{
+	int cpu;
+
+	if (!(ms_hyperv.features & HV_X64_MSR_SYNTIMER_AVAILABLE))
+		return;
+
+	for_each_online_cpu(cpu)
+		clockevents_unbind_device(hv_context.clk_evt[cpu], cpu);
+}
+
+/*
  * hv_synic_cleanup - Cleanup routine for hv_synic_init().
  */
 void hv_synic_cleanup(void *arg)
···
 
 	if (!hv_context.synic_initialized)
 		return;
+
+	/* Turn off clockevent device */
+	if (ms_hyperv.features & HV_X64_MSR_SYNTIMER_AVAILABLE)
+		hv_ce_setmode(CLOCK_EVT_MODE_SHUTDOWN,
+			      hv_context.clk_evt[cpu]);
 
 	rdmsrl(HV_X64_MSR_SINT0 + VMBUS_MESSAGE_SINT, shared_sint.as_uint64);
 

drivers/hv/hyperv_vmbus.h

···
 
 extern void hv_synic_cleanup(void *arg);
 
+extern void hv_synic_clockevents_cleanup(void);
+
 /*
  * Host version information.
  */

drivers/hv/vmbus_drv.c

···
 	int cpu;
 
 	vmbus_connection.conn_state = DISCONNECTED;
+	hv_synic_clockevents_cleanup();
 	hv_remove_vmbus_irq();
 	vmbus_free_channels();
 	bus_unregister(&hv_bus);