Drivers: hv: vmbus: Fix rescind handling

Fix the rescind handling. This patch addresses the following rescind
scenario that is currently not handled correctly:

If a rescind were to be received while the offer is still being
peocessed, we will be blocked indefinitely since the rescind message
is handled on the same work element as the offer message. Fix this
issue.

I would like to thank Dexuan Cui <decui@microsoft.com> and
Long Li <longli@microsoft.com> for working with me on this patch.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 28 insertions, 1 deletions

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 0087b49095eb..59bb3efa6e10 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -798,8 +798,10 @@ static void vmbus_device_release(struct device *device)
 	struct hv_device *hv_dev = device_to_hv_device(device);
 	struct vmbus_channel *channel = hv_dev->channel;
 
+	mutex_lock(&vmbus_connection.channel_mutex);
 	hv_process_channel_removal(channel,
 				   channel->offermsg.child_relid);
+	mutex_unlock(&vmbus_connection.channel_mutex);
 	kfree(hv_dev);
 
 }
@@ -877,7 +879,32 @@ void vmbus_on_msg_dpc(unsigned long data)
 		INIT_WORK(&ctx->work, vmbus_onmessage_work);
 		memcpy(&ctx->msg, msg, sizeof(*msg));
 
-		queue_work(vmbus_connection.work_queue, &ctx->work);
+		/*
+		 * The host can generate a rescind message while we
+		 * may still be handling the original offer. We deal with
+		 * this condition by ensuring the processing is done on the
+		 * same CPU.
+		 */
+		switch (hdr->msgtype) {
+		case CHANNELMSG_RESCIND_CHANNELOFFER:
+			/*
+			 * If we are handling the rescind message;
+			 * schedule the work on the global work queue.
+			 */
+			schedule_work_on(vmbus_connection.connect_cpu,
+					 &ctx->work);
+			break;
+
+		case CHANNELMSG_OFFERCHANNEL:
+			atomic_inc(&vmbus_connection.offer_in_progress);
+			queue_work_on(vmbus_connection.connect_cpu,
+				      vmbus_connection.work_queue,
+				      &ctx->work);
+			break;
+
+		default:
+			queue_work(vmbus_connection.work_queue, &ctx->work);
+		}
 	} else
 		entry->message_handler(hdr);