+/*
+ * vmbus_process_offer - Process the offer by creating a channel/device
+ * associated with this offer
+ */
+static void vmbus_process_offer(struct vmbus_channel *newchannel)
+{
+ struct vmbus_channel *channel;
+ struct workqueue_struct *wq;
+ unsigned long flags;
+ bool fnew = true;
+
+ mutex_lock(&vmbus_connection.channel_mutex);
+
+ /*
+ * Now that we have acquired the channel_mutex,
+ * we can release the potentially racing rescind thread.
+ */
+ atomic_dec(&vmbus_connection.offer_in_progress);
+
+ list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
+ if (!uuid_le_cmp(channel->offermsg.offer.if_type,
+ newchannel->offermsg.offer.if_type) &&
+ !uuid_le_cmp(channel->offermsg.offer.if_instance,
+ newchannel->offermsg.offer.if_instance)) {
+ fnew = false;
+ break;
+ }
+ }
+
+ if (fnew)
+ list_add_tail(&newchannel->listentry,
+ &vmbus_connection.chn_list);
+ else {
+ /*
+ * Check to see if this is a valid sub-channel.
+ */
+ if (newchannel->offermsg.offer.sub_channel_index == 0) {
+ mutex_unlock(&vmbus_connection.channel_mutex);
+ /*
+ * Don't call free_channel(), because newchannel->kobj
+ * is not initialized yet.
+ */
+ kfree(newchannel);
+ WARN_ON_ONCE(1);
+ return;
+ }
+ /*
+ * Process the sub-channel.
+ */
+ newchannel->primary_channel = channel;
+ spin_lock_irqsave(&channel->lock, flags);
+ list_add_tail(&newchannel->sc_list, &channel->sc_list);
+ spin_unlock_irqrestore(&channel->lock, flags);
+ }
+
+ mutex_unlock(&vmbus_connection.channel_mutex);
+
+ /*
+ * vmbus_process_offer() mustn't call channel->sc_creation_callback()
+ * directly for sub-channels, because sc_creation_callback() ->
+ * vmbus_open() may never get the host's response to the
+ * OPEN_CHANNEL message (the host may rescind a channel at any time,
+ * e.g. in the case of hot removing a NIC), and vmbus_onoffer_rescind()
+ * may not wake up the vmbus_open() as it's blocked due to a non-zero
+ * vmbus_connection.offer_in_progress, and finally we have a deadlock.
+ *
+ * The above is also true for primary channels, if the related device
+ * drivers use sync probing mode by default.
+ *
+ * And, usually the handling of primary channels and sub-channels can
+ * depend on each other, so we should offload them to different
+ * workqueues to avoid possible deadlock, e.g. in sync-probing mode,
+ * NIC1's netvsc_subchan_work() can race with NIC2's netvsc_probe() ->
+ * rtnl_lock(), and causes deadlock: the former gets the rtnl_lock
+ * and waits for all the sub-channels to appear, but the latter
+ * can't get the rtnl_lock and this blocks the handling of
+ * sub-channels.
+ */
+ INIT_WORK(&newchannel->add_channel_work, vmbus_add_channel_work);
+ wq = fnew ? vmbus_connection.handle_primary_chan_wq :
+ vmbus_connection.handle_sub_chan_wq;
+ queue_work(wq, &newchannel->add_channel_work);
+}
+