[PATCH V2 3/6] Drivers: hv: vmbus: Handle both rescind and offer messages in the same context

["K. Y. Srinivasan" <kys@microsoft.com>]

Execute both ressind and offer messages in the same work context. This serializes these
operations and naturally addresses the various corner cases.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
---
 - Execute blocking operations in the per-channel work elements [Dexuan Cui <decui@microsoft.com>]
 drivers/hv/channel_mgmt.c |  115 ++++++++++++++++++++++++---------------------
 1 files changed, 62 insertions(+), 53 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index b933891..f8528e1 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -134,6 +134,34 @@ fw_error:
 
 EXPORT_SYMBOL_GPL(vmbus_prep_negotiate_resp);
 
+static void vmbus_process_device_unregister(struct work_struct *work)
+{
+	struct device *dev;
+	struct vmbus_channel *channel = container_of(work,
+							struct vmbus_channel,
+							work);
+
+	dev = get_device(&channel->device_obj->device);
+	if (dev) {
+		vmbus_device_unregister(channel->device_obj);
+		put_device(dev);
+	}
+}
+
+static void vmbus_sc_creation_cb(struct work_struct *work)
+{
+	struct vmbus_channel *newchannel = container_of(work,
+							struct vmbus_channel,
+							work);
+	struct vmbus_channel *primary_channel = newchannel->primary_channel;
+
+	/*
+	 * On entry sc_creation_callback has been already verified to
+	 * be non-NULL.
+	 */
+	primary_channel->sc_creation_callback(newchannel);
+}
+
 /*
  * alloc_channel - Allocate and initialize a vmbus channel object
  */
@@ -244,29 +272,6 @@ void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid)
 	free_channel(channel);
 }
 
-/*
- * vmbus_process_rescind_offer -
- * Rescind the offer by initiating a device removal
- */
-static void vmbus_process_rescind_offer(struct work_struct *work)
-{
-	struct vmbus_channel *channel = container_of(work,
-						     struct vmbus_channel,
-						     work);
-	struct device *dev;
-
-	if (channel->device_obj) {
-		dev = get_device(&channel->device_obj->device);
-		if (dev) {
-			vmbus_device_unregister(channel->device_obj);
-			put_device(dev);
-		}
-	} else {
-		hv_process_channel_removal(channel,
-					   channel->offermsg.child_relid);
-	}
-}
-
 void vmbus_free_channels(void)
 {
 	struct vmbus_channel *channel;
@@ -281,11 +286,8 @@ void vmbus_free_channels(void)
  * vmbus_process_offer - Process the offer by creating a channel/device
  * associated with this offer
  */
-static void vmbus_process_offer(struct work_struct *work)
+static void vmbus_process_offer(struct vmbus_channel *newchannel)
 {
-	struct vmbus_channel *newchannel = container_of(work,
-							struct vmbus_channel,
-							work);
 	struct vmbus_channel *channel;
 	bool fnew = true;
 	bool enq = false;
@@ -349,9 +351,19 @@ static void vmbus_process_offer(struct work_struct *work)
 
 			newchannel->state = CHANNEL_OPEN_STATE;
 			if (channel->sc_creation_callback != NULL)
-				channel->sc_creation_callback(newchannel);
-
-			goto done_init_rescind;
+				/*
+				 * We need to invoke the sub-channel creation
+				 * callback; invoke this in a seperate work
+				 * context since we are currently running on
+				 * the global work context in which we handle
+				 * messages from the host.
+				 */
+				INIT_WORK(&newchannel->work,
+					  vmbus_sc_creation_cb);
+				queue_work(newchannel->controlwq,
+					   &newchannel->work);
+
+			return;
 		}
 
 		goto err_free_chan;
@@ -392,15 +404,9 @@ static void vmbus_process_offer(struct work_struct *work)
 		kfree(newchannel->device_obj);
 		goto err_free_chan;
 	}
-done_init_rescind:
-	spin_lock_irqsave(&newchannel->lock, flags);
-	/* The next possible work is rescind handling */
-	INIT_WORK(&newchannel->work, vmbus_process_rescind_offer);
-	/* Check if rescind offer was already received */
-	if (newchannel->rescind)
-		queue_work(newchannel->controlwq, &newchannel->work);
-	spin_unlock_irqrestore(&newchannel->lock, flags);
+
 	return;
+
 err_free_chan:
 	free_channel(newchannel);
 }
@@ -526,8 +532,7 @@ static void vmbus_onoffer(struct vmbus_channel_message_header *hdr)
 	newchannel->monitor_grp = (u8)offer->monitorid / 32;
 	newchannel->monitor_bit = (u8)offer->monitorid % 32;
 
-	INIT_WORK(&newchannel->work, vmbus_process_offer);
-	queue_work(newchannel->controlwq, &newchannel->work);
+	vmbus_process_offer(newchannel);
 }
 
 /*
@@ -544,24 +549,28 @@ static void vmbus_onoffer_rescind(struct vmbus_channel_message_header *hdr)
 	rescind = (struct vmbus_channel_rescind_offer *)hdr;
 	channel = relid2channel(rescind->child_relid);
 
-	if (channel == NULL)
-		/* Just return here, no channel found */
+	if (channel == NULL) {
+		hv_process_channel_removal(NULL, rescind->child_relid);
 		return;
+	}
 
 	spin_lock_irqsave(&channel->lock, flags);
 	channel->rescind = true;
-	/*
-	 * channel->work.func != vmbus_process_rescind_offer means we are still
-	 * processing offer request and the rescind offer processing should be
-	 * postponed. It will be done at the very end of vmbus_process_offer()
-	 * as rescind flag is being checked there.
-	 */
-	if (channel->work.func == vmbus_process_rescind_offer)
-		/* work is initialized for vmbus_process_rescind_offer() from
-		 * vmbus_process_offer() where the channel got created */
-		queue_work(channel->controlwq, &channel->work);
-
 	spin_unlock_irqrestore(&channel->lock, flags);
+
+	if (channel->device_obj) {
+		/*
+		 * We will have to unregister this device from the
+		 * driver core. Do this in the per-channel work context.
+		 * Note that we are currently executing on the global
+		 * workq for handling messages from the host.
+		 */
+		INIT_WORK(&channel->work, vmbus_process_device_unregister);
+		queue_work(channel->controlwq, &channel->work);
+	} else {
+		hv_process_channel_removal(channel,
+					   channel->offermsg.child_relid);
+	}
 }
 
 /*
-- 
1.7.4.1