Drivers: hv: vmbus: Remove unnecessary channel->lock critical sections (sc_list readers)

Additions/deletions to/from sc_list (as well as modifications of
target_cpu(s)) are protected by channel_mutex, which hv_synic_cleanup()
and vmbus_bus_suspend() own for the duration of the channel->lock
critical section in question.

Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Link: https://lore.kernel.org/r/20200617164642.37393-5-parri.andrea@gmail.com
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>

Author: andrea-parri

drivers/hv/hv.c

@@ -241,7 +241,6 @@ int hv_synic_cleanup(unsigned int cpu)
 {
 	struct vmbus_channel *channel, *sc;
 	bool channel_found = false;
-	unsigned long flags;
 
 	/*
 	 * Hyper-V does not provide a way to change the connect CPU once
@@ -263,14 +262,12 @@ int hv_synic_cleanup(unsigned int cpu)
 			channel_found = true;
 			break;
 		}
-		spin_lock_irqsave(&channel->lock, flags);
 		list_for_each_entry(sc, &channel->sc_list, sc_list) {
 			if (sc->target_cpu == cpu) {
 				channel_found = true;
 				break;
 			}
 		}
-		spin_unlock_irqrestore(&channel->lock, flags);
 		if (channel_found)
 			break;
 	}

drivers/hv/vmbus_drv.c

@@ -2344,7 +2344,6 @@ static int vmbus_acpi_add(struct acpi_device *device)
 static int vmbus_bus_suspend(struct device *dev)
 {
 	struct vmbus_channel *channel, *sc;
-	unsigned long flags;
 
 	while (atomic_read(&vmbus_connection.offer_in_progress) != 0) {
 		/*
@@ -2402,12 +2401,10 @@ static int vmbus_bus_suspend(struct device *dev)
 			continue;
 		}
 
-		spin_lock_irqsave(&channel->lock, flags);
 		list_for_each_entry(sc, &channel->sc_list, sc_list) {
 			pr_err("Sub-channel not deleted!\n");
 			WARN_ON_ONCE(1);
 		}
-		spin_unlock_irqrestore(&channel->lock, flags);
 
 		atomic_inc(&vmbus_connection.nr_chan_fixup_on_resume);
 	}