4 files changed, 31 insertions, 27 deletions

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 74e77de89b4f..f4bd306d2cef 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -69,7 +69,6 @@ MODULE_PARM_DESC(max_version,
 int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo, u32 version)
 {
 	int ret = 0;
-	unsigned int cur_cpu;
 	struct vmbus_channel_initiate_contact *msg;
 	unsigned long flags;
 
@@ -102,24 +101,7 @@ int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo, u32 version)
 
 	msg->monitor_page1 = virt_to_phys(vmbus_connection.monitor_pages[0]);
 	msg->monitor_page2 = virt_to_phys(vmbus_connection.monitor_pages[1]);
-	/*
-	 * We want all channel messages to be delivered on CPU 0.
-	 * This has been the behavior pre-win8. This is not
-	 * perf issue and having all channel messages delivered on CPU 0
-	 * would be ok.
-	 * For post win8 hosts, we support receiving channel messagges on
-	 * all the CPUs. This is needed for kexec to work correctly where
-	 * the CPU attempting to connect may not be CPU 0.
-	 */
-	if (version >= VERSION_WIN8_1) {
-		cur_cpu = get_cpu();
-		msg->target_vcpu = hv_cpu_number_to_vp_number(cur_cpu);
-		vmbus_connection.connect_cpu = cur_cpu;
-		put_cpu();
-	} else {
-		msg->target_vcpu = 0;
-		vmbus_connection.connect_cpu = 0;
-	}
+	msg->target_vcpu = hv_cpu_number_to_vp_number(VMBUS_CONNECT_CPU);
 
 	/*
 	 * Add to list before we send the request since we may
diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index 6098e0cbdb4b..e2b331045464 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -250,6 +250,13 @@ int hv_synic_cleanup(unsigned int cpu)
 	unsigned long flags;
 
 	/*
+	 * Hyper-V does not provide a way to change the connect CPU once
+	 * it is set; we must prevent the connect CPU from going offline.
+	 */
+	if (cpu == VMBUS_CONNECT_CPU)
+		return -EBUSY;
+
+	/*
 	 * Search for channels which are bound to the CPU we're about to
 	 * cleanup. In case we find one and vmbus is still connected we need to
 	 * fail, this will effectively prevent CPU offlining. There is no way
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index ab560ac9c040..000740d053a2 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -212,12 +212,13 @@ enum vmbus_connect_state {
 
 #define MAX_SIZE_CHANNEL_MESSAGE	HV_MESSAGE_PAYLOAD_BYTE_COUNT
 
-struct vmbus_connection {
-	/*
-	 * CPU on which the initial host contact was made.
-	 */
-	int connect_cpu;
+/*
+ * The CPU that Hyper-V will interrupt for VMBUS messages, such as
+ * CHANNELMSG_OFFERCHANNEL and CHANNELMSG_RESCIND_CHANNELOFFER.
+ */
+#define VMBUS_CONNECT_CPU	0
 
+struct vmbus_connection {
 	u32 msg_conn_id;
 
 	atomic_t offer_in_progress;
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 3a05e1bc359c..495337ec68f1 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1109,14 +1109,28 @@ void vmbus_on_msg_dpc(unsigned long data)
 			/*
 			 * If we are handling the rescind message;
 			 * schedule the work on the global work queue.
+			 *
+			 * The OFFER message and the RESCIND message should
+			 * not be handled by the same serialized work queue,
+			 * because the OFFER handler may call vmbus_open(),
+			 * which tries to open the channel by sending an
+			 * OPEN_CHANNEL message to the host and waits for
+			 * the host's response; however, if the host has
+			 * rescinded the channel before it receives the
+			 * OPEN_CHANNEL message, the host just silently
+			 * ignores the OPEN_CHANNEL message; as a result,
+			 * the guest's OFFER handler hangs for ever, if we
+			 * handle the RESCIND message in the same serialized
+			 * work queue: the RESCIND handler can not start to
+			 * run before the OFFER handler finishes.
 			 */
-			schedule_work_on(vmbus_connection.connect_cpu,
+			schedule_work_on(VMBUS_CONNECT_CPU,
 					 &ctx->work);
 			break;
 
 		case CHANNELMSG_OFFERCHANNEL:
 			atomic_inc(&vmbus_connection.offer_in_progress);
-			queue_work_on(vmbus_connection.connect_cpu,
+			queue_work_on(VMBUS_CONNECT_CPU,
 				      vmbus_connection.work_queue,
 				      &ctx->work);
 			break;
@@ -1164,7 +1178,7 @@ static void vmbus_force_channel_rescinded(struct vmbus_channel *channel)
 
 	INIT_WORK(&ctx->work, vmbus_onmessage_work);
 
-	queue_work_on(vmbus_connection.connect_cpu,
+	queue_work_on(VMBUS_CONNECT_CPU,
 		      vmbus_connection.work_queue,
 		      &ctx->work);
 }