Re: [RFC 11/12] Drivers: hv: vmbus: Wait for MODIFYCHANNEL to finish when offlining CPUs

[Boqun Feng]

Hi Michael,

On Mon, Jun 03, 2024 at 10:09:39PM -0700, mhkelley58@xxxxxxxxx wrote:
[...]
> diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
> index bf35bb40c55e..571b2955b38e 100644
> --- a/drivers/hv/hyperv_vmbus.h
> +++ b/drivers/hv/hyperv_vmbus.h
> @@ -264,6 +264,14 @@ struct vmbus_connection {
>  	struct irq_domain *vmbus_irq_domain;
>  	struct irq_chip	vmbus_irq_chip;
>  
> +	/*
> +	 * VM-wide counts of MODIFYCHANNEL messages sent and completed.
> +	 * Used when taking a CPU offline to make sure the relevant
> +	 * MODIFYCHANNEL messages have been completed.
> +	 */
> +	u64 modchan_sent;
> +	u64 modchan_completed;
> +

Looks to me, we can just use atomic64_t here: modifying channels is far
from hotpath, so the cost of atomic increment is not a big issue, and we
avoid possible data races now and in the future.

Thoughts?

Regards,
Boqun

>  	/*
>  	 * An offer message is handled first on the work_queue, and then
>  	 * is further handled on handle_primary_chan_wq or
> -- 
> 2.25.1
>