Patch "[PATCH 041/135] Drivers: hv: vmbus: fix rescind-offer handling for" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

[PATCH 041/135] Drivers: hv: vmbus: fix rescind-offer handling for

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
0041-Drivers-hv-vmbus-fix-rescind-offer-handling-for-devi.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Dexuan Cui <[email protected]>
Date: Mon, 14 Dec 2015 16:01:49 -0800
Subject: [PATCH 041/135] Drivers: hv: vmbus: fix rescind-offer handling for
device without a driver

[ Upstream commit 34c6801e3310ad286c7bb42bc88d42926b8f99bf ]

In the path vmbus_onoffer_rescind() -> vmbus_device_unregister() -> device_unregister() -> ... -> __device_release_driver(), we can see for a device without a driver loaded: dev->driver is NULL, so dev->bus->remove(dev), namely vmbus_remove(), isn't invoked.

As a result, vmbus_remove() -> hv_process_channel_removal() isn't invoked and some cleanups(like sending a CHANNELMSG_RELID_RELEASED message to the host) aren't done.

We can demo the issue this way:
1. rmmod hv_utils;
2. disable the Heartbeat Integration Service in Hyper-V Manager and lsvmbus shows the device disappears.
3. re-enable the Heartbeat in Hyper-V Manager and modprobe hv_utils, but lsvmbus shows the device can't appear again.
This is because, the host thinks the VM hasn't released the relid, so can't re-offer the device to the VM.

We can fix the issue by moving hv_process_channel_removal() from vmbus_close_internal() to vmbus_device_release(), since the latter is always invoked on device_unregister(), whether or not the dev has a driver loaded.

---
 drivers/hv/channel.c      |    6 ------
 drivers/hv/channel_mgmt.c |    6 +++---
 drivers/hv/vmbus_drv.c    |   15 +++------------
 3 files changed, 6 insertions(+), 21 deletions(-)

@@ -563,12 +563,6 @@ static int vmbus_close_internal(struct v
 	free_pages((unsigned long)channel->ringbuffer_pages,
 		get_order(channel->ringbuffer_pagecount * PAGE_SIZE));
 
-	/*
-	 * If the channel has been rescinded; process device removal.
-	 */
-	if (channel->rescind)
-		hv_process_channel_removal(channel,
-					   channel->offermsg.child_relid);
 out:
 	tasklet_enable(tasklet);
 

@@ -191,6 +191,8 @@ void hv_process_channel_removal(struct v
 	if (channel == NULL)
 		return;
 
+	BUG_ON(!channel->rescind);
+
 	if (channel->target_cpu != get_cpu()) {
 		put_cpu();
 		smp_call_function_single(channel->target_cpu,

@@ -230,9 +232,7 @@ void vmbus_free_channels(void)
 
 	list_for_each_entry_safe(channel, tmp, &vmbus_connection.chn_list,
 		listentry) {
-		/* if we don't set rescind to true, vmbus_close_internal()
-		 * won't invoke hv_process_channel_removal().
-		 */
+		/* hv_process_channel_removal() needs this */
 		channel->rescind = true;
 
 		vmbus_device_unregister(channel->device_obj);

@@ -603,23 +603,11 @@ static int vmbus_remove(struct device *c
 {
 	struct hv_driver *drv;
 	struct hv_device *dev = device_to_hv_device(child_device);
-	u32 relid = dev->channel->offermsg.child_relid;
 
 	if (child_device->driver) {
 		drv = drv_to_hv_drv(child_device->driver);
 		if (drv->remove)
 			drv->remove(dev);
-		else {
-			hv_process_channel_removal(dev->channel, relid);
-			pr_err("remove not set for driver %s\n",
-				dev_name(child_device));
-		}
-	} else {
-		/*
-		 * We don't have a driver for this device; deal with the
-		 * rescind message by removing the channel.
-		 */
-		hv_process_channel_removal(dev->channel, relid);
 	}
 
 	return 0;

@@ -654,7 +642,10 @@ static void vmbus_shutdown(struct device
 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;
 
+	hv_process_channel_removal(channel,
+				   channel->offermsg.child_relid);
 	kfree(hv_dev);
 
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/0118-clocksource-Allow-unregistering-the-watchdog.patch queue-4.4/0041-Drivers-hv-vmbus-fix-rescind-offer-handling-for-devi.patch queue-4.4/0040-Drivers-hv-vmbus-serialize-process_chn_event-and-vmb.patch