fcf8d36c46
We'll remove the per-channel control_work_queue because it can't properly do serialization of message handling, e.g., when there are 2 NIC devices, vmbus_channel_on_offer() -> hv_queue_work_item() has a race condition: for an SMP VM, vmbus_channel_process_offer() can run concurrently on different CPUs and if the second NIC's vmbus_channel_process_offer() -> hv_vmbus_child_device_register() runs first, the second NIC's name will be hn0 and the first NIC's name will be hn1! We can fix the race condition by removing the per-channel control_work_queue and run all the message handlers in the global hv_vmbus_g_connection.work_queue -- we'll do this in the next patch. With the coming next patch, we have to run the non-blocking handlers directly in the kernel thread vmbus_msg_swintr(), because the special handling of sub-channel: when a sub-channel (e.g., of the storvsc driver) is received and being handled in vmbus_channel_on_offer() running on the global hv_vmbus_g_connection.work_queue, vmbus_channel_process_offer() invokes channel->sc_creation_callback, i.e., storvsc_handle_sc_creation, and the callback will invoke hv_vmbus_channel_open() -> hv_vmbus_post_message and expect a further reply from the host, but the handling of the further messag can't be done because the current message's handling hasn't finished yet; as result, hv_vmbus_channel_open() -> sema_timedwait() will time out and th device can't work. Also renamed the handler type from hv_pfn_channel_msg_handler to vmbus_msg_handler: the 'pfn' and 'channel' in the old name make no sense. Submitted by: Dexuan Cui <decui microsoft com> Reviewed by: royger MFC after: 2 weeks Differential Revision: https://reviews.freebsd.org/D4596
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