hv: don't schedule new works in vmbus_onoffer()/vmbus_onoffer_rescind()

Since the 2 fucntions can safely run in vmbus_connection.work_queue without
hang, we don't need to schedule new work items into the per-channel workqueue.

Actally we can even remove the per-channel workqueue now -- we'll do it
in the next patch.
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/channel_mgmt.c

@@ -23,7 +23,6 @@
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/wait.h>
-#include <linux/delay.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/list.h>
@@ -33,11 +32,6 @@
 
 #include "hyperv_vmbus.h"
 
-struct vmbus_rescind_work {
-	struct work_struct work;
-	struct vmbus_channel *channel;
-};
-
 /**
  * vmbus_prep_negotiate_resp() - Create default response for Hyper-V Negotiate message
  * @icmsghdrp: Pointer to msg header structure
@@ -134,20 +128,6 @@ bool vmbus_prep_negotiate_resp(struct icmsg_hdr *icmsghdrp,
 
 EXPORT_SYMBOL_GPL(vmbus_prep_negotiate_resp);
 
-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
  */
@@ -206,40 +186,6 @@ static void free_channel(struct vmbus_channel *channel)
 	queue_work(vmbus_connection.work_queue, &channel->work);
 }
 
-static void process_rescind_fn(struct work_struct *work)
-{
-	struct vmbus_rescind_work *rc_work;
-	struct vmbus_channel *channel;
-	struct device *dev;
-
-	rc_work = container_of(work, struct vmbus_rescind_work, work);
-	channel = rc_work->channel;
-
-	/*
-	 * We have already acquired a reference on the channel
-	 * and so it cannot vanish underneath us.
-	 * It is possible (while very unlikely) that we may
-	 * get here while the processing of the initial offer
-	 * is still not complete. Deal with this situation by
-	 * just waiting until the channel is in the correct state.
-	 */
-
-	while (channel->work.func != release_channel)
-		msleep(1000);
-
-	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);
-	}
-	kfree(work);
-}
-
 static void percpu_channel_enq(void *arg)
 {
 	struct vmbus_channel *channel = arg;
@@ -302,46 +248,6 @@ void vmbus_free_channels(void)
 	}
 }
 
-static void vmbus_do_device_register(struct work_struct *work)
-{
-	struct hv_device *device_obj;
-	int ret;
-	unsigned long flags;
-	struct vmbus_channel *newchannel = container_of(work,
-						     struct vmbus_channel,
-						     work);
-
-	ret = vmbus_device_register(newchannel->device_obj);
-	if (ret != 0) {
-		pr_err("unable to add child device object (relid %d)\n",
-			newchannel->offermsg.child_relid);
-		spin_lock_irqsave(&vmbus_connection.channel_lock, flags);
-		list_del(&newchannel->listentry);
-		device_obj = newchannel->device_obj;
-		newchannel->device_obj = NULL;
-		spin_unlock_irqrestore(&vmbus_connection.channel_lock, flags);
-
-		if (newchannel->target_cpu != get_cpu()) {
-			put_cpu();
-			smp_call_function_single(newchannel->target_cpu,
-					 percpu_channel_deq, newchannel, true);
-		} else {
-			percpu_channel_deq(newchannel);
-			put_cpu();
-		}
-
-		kfree(device_obj);
-		if (!newchannel->rescind) {
-			free_channel(newchannel);
-			return;
-		}
-	}
-	/*
-	 * The next state for this channel is to be freed.
-	 */
-	INIT_WORK(&newchannel->work, release_channel);
-}
-
 /*
  * vmbus_process_offer - Process the offer by creating a channel/device
  * associated with this offer
@@ -410,19 +316,8 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
 
 			newchannel->state = CHANNEL_OPEN_STATE;
 			channel->num_sc++;
-			if (channel->sc_creation_callback != NULL) {
-				/*
-				 * 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);
-			}
+			if (channel->sc_creation_callback != NULL)
+				channel->sc_creation_callback(newchannel);
 
 			return;
 		}
@@ -453,13 +348,13 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
 	 * Add the new device to the bus. This will kick off device-driver
 	 * binding which eventually invokes the device driver's AddDevice()
 	 * method.
-	 * Invoke this call on the per-channel work context.
-	 * Until we return from this function, rescind offer message
-	 * cannot be processed as we are running on the global message
-	 * handling work.
 	 */
-	INIT_WORK(&newchannel->work, vmbus_do_device_register);
-	queue_work(newchannel->controlwq, &newchannel->work);
+	if (vmbus_device_register(newchannel->device_obj) != 0) {
+		pr_err("unable to add child device object (relid %d)\n",
+			newchannel->offermsg.child_relid);
+		kfree(newchannel->device_obj);
+		goto err_deq_chan;
+	}
 	return;
 
 err_deq_chan:
@@ -613,31 +508,35 @@ static void vmbus_onoffer_rescind(struct vmbus_channel_message_header *hdr)
 {
 	struct vmbus_channel_rescind_offer *rescind;
 	struct vmbus_channel *channel;
-	struct vmbus_rescind_work *rc_work;
+	unsigned long flags;
+	struct device *dev;
 
 	rescind = (struct vmbus_channel_rescind_offer *)hdr;
-	channel = relid2channel(rescind->child_relid, true);
+	channel = relid2channel(rescind->child_relid);
 
 	if (channel == NULL) {
 		hv_process_channel_removal(NULL, rescind->child_relid);
 		return;
 	}
 
-	/*
-	 * We have acquired a reference on the channel and have posted
-	 * the rescind state. Perform further cleanup in a work context
-	 * that is different from the global work context in which
-	 * we process messages from the host (we are currently executing
-	 * on that global context.
-	 */
-	rc_work = kzalloc(sizeof(struct vmbus_rescind_work), GFP_KERNEL);
-	if (!rc_work) {
-		pr_err("Unable to allocate memory for rescind processing ");
-		return;
+	spin_lock_irqsave(&channel->lock, flags);
+	channel->rescind = true;
+	spin_unlock_irqrestore(&channel->lock, flags);
+
+	if (channel->device_obj) {
+		/*
+		 * We will have to unregister this device from the
+		 * driver core.
+		 */
+		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);
 	}
-	rc_work->channel = channel;
-	INIT_WORK(&rc_work->work, process_rescind_fn);
-	schedule_work(&rc_work->work);
 }
 
 /*

drivers/hv/connection.c

@@ -270,7 +270,7 @@ static struct vmbus_channel *pcpu_relid2channel(u32 relid)
  * relid2channel - Get the channel object given its
  * child relative id (ie channel id)
  */
-struct vmbus_channel *relid2channel(u32 relid, bool rescind)
+struct vmbus_channel *relid2channel(u32 relid)
 {
 	struct vmbus_channel *channel;
 	struct vmbus_channel *found_channel  = NULL;
@@ -282,8 +282,6 @@ struct vmbus_channel *relid2channel(u32 relid, bool rescind)
 	list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
 		if (channel->offermsg.child_relid == relid) {
 			found_channel = channel;
-			if (rescind)
-				found_channel->rescind = true;
 			break;
 		} else if (!list_empty(&channel->sc_list)) {
 			/*
@@ -294,8 +292,6 @@ struct vmbus_channel *relid2channel(u32 relid, bool rescind)
 							sc_list);
 				if (cur_sc->offermsg.child_relid == relid) {
 					found_channel = cur_sc;
-					if (rescind)
-						found_channel->rescind = true;
 					break;
 				}
 			}

drivers/hv/hyperv_vmbus.h

@@ -715,7 +715,7 @@ void vmbus_device_unregister(struct hv_device *device_obj);
 /* VmbusChildDeviceDestroy( */
 /* struct hv_device *); */
 
-struct vmbus_channel *relid2channel(u32 relid, bool rescind);
+struct vmbus_channel *relid2channel(u32 relid);
 
 void vmbus_free_channels(void);