netdev - RE: [PATCH net-next 1/1] hv_netvsc: Wait for sub-channels to be processed during probe

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Message-ID: <4fd650437f864cf2a58e8334253f5dcd@SIXPR30MB031.064d.mgd.msft.net>
Date:	Fri, 17 Jul 2015 10:00:43 +0000
From:	Dexuan Cui <decui@...rosoft.com>
To:	KY Srinivasan <kys@...rosoft.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"vkuznets@...hat.com" <vkuznets@...hat.com>
CC:	KY Srinivasan <kys@...rosoft.com>
Subject: RE: [PATCH net-next 1/1] hv_netvsc: Wait for sub-channels to be
 processed during probe

> From: K. Y. Srinivasan 
> Sent: Friday, July 17, 2015 3:17
> Subject: [PATCH net-next 1/1] hv_netvsc: Wait for sub-channels to be processed
> during probe
> diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
> ...
> @@ -1116,6 +1127,9 @@ int rndis_filter_device_add(struct hv_device *dev,
>  	num_possible_rss_qs = cpumask_weight(node_cpu_mask);
>  	net_device->num_chn = min(num_possible_rss_qs, num_rss_qs);
> 
> +	num_rss_qs = net_device->num_chn - 1;
> +	net_device->num_sc_offered = num_rss_qs;
> +
>  	if (net_device->num_chn == 1)
>  		goto out;
> 
> @@ -1157,11 +1171,22 @@ int rndis_filter_device_add(struct hv_device *dev,
> 
>  	ret = rndis_filter_set_rss_param(rndis_device, net_device->num_chn);
> 
> +	/*
> +	 * Wait for the host to send us the sub-channel offers.
> +	 */
> +	spin_lock_irqsave(&net_device->sc_lock, flags);
> +	sc_delta = net_device->num_chn - 1 - num_rss_qs;
> +	net_device->num_sc_offered -= sc_delta;

Hi KY,
IMO here the "-= " should be "+="?

I think sc_delta is usually <= 0, meaning the host may allocate less subchannels than
we expect.
With "-=", net_device->num_sc_offered can become bigger -- this doesn't seem correct.

Why not use 
"net_device->num_sc_offered = net_device->num_chn - 1;" directly?
At this point, net_device->num_chn has been the number of the actual channels.


> +	spin_unlock_irqrestore(&net_device->sc_lock, flags);
> +
> +	if (net_device->num_sc_offered != 0)
> +		wait_for_completion(&net_device->channel_init_wait);

BTW, I also tested the patch and I can confirm the panic I saw disappeared with the patch.

-- Dexuan
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