Drivers: hv: vmbus: Fix a siganlling host signalling issue

Handle the case when the write to the ringbuffer fails. In this case,
unconditionally signal the host. Since we may have deferred signalling
the host based on the kick_q parameter, signalling the host
unconditionally in this case deals with the issue.
Signed-off-by: NK. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/channel.c

@@ -611,7 +611,19 @@ int vmbus_sendpacket_ctl(struct vmbus_channel *channel, void *buffer,
 
 	ret = hv_ringbuffer_write(&channel->outbound, bufferlist, 3, &signal);
 
-	if ((ret == 0) && kick_q && signal)
+	/*
+	 * Signalling the host is conditional on many factors:
+	 * 1. The ring state changed from being empty to non-empty.
+	 *    This is tracked by the variable "signal".
+	 * 2. The variable kick_q tracks if more data will be placed
+	 *    on the ring. We will not signal if more data is
+	 *    to be placed.
+	 *
+	 * If we cannot write to the ring-buffer; signal the host
+	 * even if we may not have written anything. This is a rare
+	 * enough condition that it should not matter.
+	 */
+	if (((ret == 0) && kick_q && signal) || (ret))
 		vmbus_setevent(channel);
 
 	return ret;
@@ -702,7 +714,19 @@ int vmbus_sendpacket_pagebuffer_ctl(struct vmbus_channel *channel,
 
 	ret = hv_ringbuffer_write(&channel->outbound, bufferlist, 3, &signal);
 
-	if ((ret == 0) && kick_q && signal)
+	/*
+	 * Signalling the host is conditional on many factors:
+	 * 1. The ring state changed from being empty to non-empty.
+	 *    This is tracked by the variable "signal".
+	 * 2. The variable kick_q tracks if more data will be placed
+	 *    on the ring. We will not signal if more data is
+	 *    to be placed.
+	 *
+	 * If we cannot write to the ring-buffer; signal the host
+	 * even if we may not have written anything. This is a rare
+	 * enough condition that it should not matter.
+	 */
+	if (((ret == 0) && kick_q && signal) || (ret))
 		vmbus_setevent(channel);
 
 	return ret;