3 files changed, 61 insertions, 20 deletions

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 38b682bab85a..b6c1211b4df7 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -597,27 +597,55 @@ static void init_vp_index(struct vmbus_channel *channel, u16 dev_type)
 
 static void vmbus_wait_for_unload(void)
 {
-	int cpu = smp_processor_id();
-	void *page_addr = hv_context.synic_message_page[cpu];
-	struct hv_message *msg = (struct hv_message *)page_addr +
-				  VMBUS_MESSAGE_SINT;
+	int cpu;
+	void *page_addr;
+	struct hv_message *msg;
 	struct vmbus_channel_message_header *hdr;
-	bool unloaded = false;
+	u32 message_type;
 
+	/*
+	 * CHANNELMSG_UNLOAD_RESPONSE is always delivered to the CPU which was
+	 * used for initial contact or to CPU0 depending on host version. When
+	 * we're crashing on a different CPU let's hope that IRQ handler on
+	 * the cpu which receives CHANNELMSG_UNLOAD_RESPONSE is still
+	 * functional and vmbus_unload_response() will complete
+	 * vmbus_connection.unload_event. If not, the last thing we can do is
+	 * read message pages for all CPUs directly.
+	 */
 	while (1) {
-		if (READ_ONCE(msg->header.message_type) == HVMSG_NONE) {
-			mdelay(10);
-			continue;
-		}
+		if (completion_done(&vmbus_connection.unload_event))
+			break;
 
-		hdr = (struct vmbus_channel_message_header *)msg->u.payload;
-		if (hdr->msgtype == CHANNELMSG_UNLOAD_RESPONSE)
-			unloaded = true;
+		for_each_online_cpu(cpu) {
+			page_addr = hv_context.synic_message_page[cpu];
+			msg = (struct hv_message *)page_addr +
+				VMBUS_MESSAGE_SINT;
 
-		vmbus_signal_eom(msg);
+			message_type = READ_ONCE(msg->header.message_type);
+			if (message_type == HVMSG_NONE)
+				continue;
 
-		if (unloaded)
-			break;
+			hdr = (struct vmbus_channel_message_header *)
+				msg->u.payload;
+
+			if (hdr->msgtype == CHANNELMSG_UNLOAD_RESPONSE)
+				complete(&vmbus_connection.unload_event);
+
+			vmbus_signal_eom(msg, message_type);
+		}
+
+		mdelay(10);
+	}
+
+	/*
+	 * We're crashing and already got the UNLOAD_RESPONSE, cleanup all
+	 * maybe-pending messages on all CPUs to be able to receive new
+	 * messages after we reconnect.
+	 */
+	for_each_online_cpu(cpu) {
+		page_addr = hv_context.synic_message_page[cpu];
+		msg = (struct hv_message *)page_addr + VMBUS_MESSAGE_SINT;
+		msg->header.message_type = HVMSG_NONE;
 	}
 }
 
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index e5203e4d6782..718b5c72f0c8 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -625,9 +625,21 @@ extern struct vmbus_channel_message_table_entry
 	channel_message_table[CHANNELMSG_COUNT];
 
 /* Free the message slot and signal end-of-message if required */
-static inline void vmbus_signal_eom(struct hv_message *msg)
+static inline void vmbus_signal_eom(struct hv_message *msg, u32 old_msg_type)
 {
-	msg->header.message_type = HVMSG_NONE;
+	/*
+	 * On crash we're reading some other CPU's message page and we need
+	 * to be careful: this other CPU may already had cleared the header
+	 * and the host may already had delivered some other message there.
+	 * In case we blindly write msg->header.message_type we're going
+	 * to lose it. We can still lose a message of the same type but
+	 * we count on the fact that there can only be one
+	 * CHANNELMSG_UNLOAD_RESPONSE and we don't care about other messages
+	 * on crash.
+	 */
+	if (cmpxchg(&msg->header.message_type, old_msg_type,
+		    HVMSG_NONE) != old_msg_type)
+		return;
 
 	/*
 	 * Make sure the write to MessageType (ie set to
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index a29a6c0abc01..952f20fdc7e3 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -712,7 +712,7 @@ static void hv_process_timer_expiration(struct hv_message *msg, int cpu)
 	if (dev->event_handler)
 		dev->event_handler(dev);
 
-	vmbus_signal_eom(msg);
+	vmbus_signal_eom(msg, HVMSG_TIMER_EXPIRED);
 }
 
 void vmbus_on_msg_dpc(unsigned long data)
@@ -724,8 +724,9 @@ void vmbus_on_msg_dpc(unsigned long data)
 	struct vmbus_channel_message_header *hdr;
 	struct vmbus_channel_message_table_entry *entry;
 	struct onmessage_work_context *ctx;
+	u32 message_type = msg->header.message_type;
 
-	if (msg->header.message_type == HVMSG_NONE)
+	if (message_type == HVMSG_NONE)
 		/* no msg */
 		return;
 
@@ -750,7 +751,7 @@ void vmbus_on_msg_dpc(unsigned long data)
 		entry->message_handler(hdr);
 
 msg_handled:
-	vmbus_signal_eom(msg);
+	vmbus_signal_eom(msg, message_type);
 }
 
 static void vmbus_isr(void)