Drivers: hv: vmbus: Remove the lock field from the vmbus_channel struct

The spinlock is (now) *not used to protect test-and-set accesses
to attributes of the structure or sc_list operations.

There is, AFAICT, a distinct lack of {WRITE,READ}_ONCE()s in the
handling of channel->state, but the changes below do not seem to
make things "worse".  ;-)

Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Link: https://lore.kernel.org/r/20200617164642.37393-9-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/channel.c

@@ -129,12 +129,8 @@ static int __vmbus_open(struct vmbus_channel *newchannel,
 	send_pages = newchannel->ringbuffer_send_offset;
 	recv_pages = newchannel->ringbuffer_pagecount - send_pages;
 
-	spin_lock_irqsave(&newchannel->lock, flags);
-	if (newchannel->state != CHANNEL_OPEN_STATE) {
-		spin_unlock_irqrestore(&newchannel->lock, flags);
+	if (newchannel->state != CHANNEL_OPEN_STATE)
 		return -EINVAL;
-	}
-	spin_unlock_irqrestore(&newchannel->lock, flags);
 
 	newchannel->state = CHANNEL_OPENING_STATE;
 	newchannel->onchannel_callback = onchannelcallback;

drivers/hv/channel_mgmt.c

@@ -317,7 +317,6 @@ static struct vmbus_channel *alloc_channel(void)
 		return NULL;
 
 	spin_lock_init(&channel->sched_lock);
-	spin_lock_init(&channel->lock);
 	init_completion(&channel->rescind_event);
 
 	INIT_LIST_HEAD(&channel->sc_list);

include/linux/hyperv.h

@@ -840,12 +840,6 @@ struct vmbus_channel {
 	 */
 	void (*chn_rescind_callback)(struct vmbus_channel *channel);
 
-	/*
-	 * The spinlock to protect the structure. It is being used to protect
-	 * test-and-set access to various attributes of the structure as well
-	 * as all sc_list operations.
-	 */
-	spinlock_t lock;
 	/*
 	 * All Sub-channels of a primary channel are linked here.
 	 */