[PATCH 2/4] Drivers: hv: vmbus: do not lose rescind offer on failure in vmbus_process_offer()

[Vitaly Kuznetsov <vkuznets@redhat.com>]

In case we hit a failure condition in vmbus_process_offer() and a rescind offer
was pending for the channel we just do free_channel() so CHANNELMSG_RELID_RELEASED
will never be send to the host. We have to follow vmbus_process_rescind_offer()
path anyway.

To support the change we need to protect list_del in vmbus_process_rescind_offer()
hitting an uninitialized list.

Reported-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 drivers/hv/channel_mgmt.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index eb9ce94..fdccd16 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -152,6 +152,7 @@ static struct vmbus_channel *alloc_channel(void)
 	spin_lock_init(&channel->inbound_lock);
 	spin_lock_init(&channel->lock);
 
+	INIT_LIST_HEAD(&channel->listentry);
 	INIT_LIST_HEAD(&channel->sc_list);
 	INIT_LIST_HEAD(&channel->percpu_list);
 
@@ -308,6 +309,7 @@ static void vmbus_process_offer(struct work_struct *work)
 	struct vmbus_channel *channel;
 	bool fnew = true;
 	bool enq = false;
+	bool failure = false;
 	int ret;
 	unsigned long flags;
 
@@ -408,19 +410,33 @@ static void vmbus_process_offer(struct work_struct *work)
 		spin_lock_irqsave(&vmbus_connection.channel_lock, flags);
 		list_del(&newchannel->listentry);
 		spin_unlock_irqrestore(&vmbus_connection.channel_lock, flags);
+		/*
+		 * Init listentry again as vmbus_process_rescind_offer can try
+		 * doing list_del again.
+		 */
+		INIT_LIST_HEAD(&channel->listentry);
 		kfree(newchannel->device_obj);
+		newchannel->device_obj = NULL;
 		goto err_free_chan;
 	}
+	goto done_init_rescind;
+err_free_chan:
+	failure = true;
 done_init_rescind:
+	/*
+	 * Get additional reference as vmbus_put_channel() can be called
+	 * either directly or through vmbus_process_rescind_offer().
+	 */
+	vmbus_get_channel(newchannel);
 	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);
+	else if (failure)
+		vmbus_put_channel(newchannel);
 	spin_unlock_irqrestore(&newchannel->lock, flags);
-	return;
-err_free_chan:
 	vmbus_put_channel(newchannel);
 }
 
-- 
1.9.3