linux-kernel - Re: [PATCH net-next v3] netvsc: get rid of completion timeouts

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Date:	Thu, 09 Jun 2016 11:43:17 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	vkuznets@...hat.com
Cc:	netdev@...r.kernel.org, devel@...uxdriverproject.org,
	linux-kernel@...r.kernel.org, kys@...rosoft.com,
	haiyangz@...rosoft.com
Subject: Re: [PATCH net-next v3] netvsc: get rid of completion timeouts

From: Vitaly Kuznetsov <vkuznets@...hat.com>
Date: Thu,  9 Jun 2016 12:44:03 +0200

> I'm hitting 5 second timeout in rndis_filter_set_rss_param() while setting
> RSS parameters for the device. When this happens we end up returning
> -ETIMEDOUT from the function and rndis_filter_device_add() falls back to
> setting
> 
>         net_device->max_chn = 1;
>         net_device->num_chn = 1;
>         net_device->num_sc_offered = 0;
> 
> but after a moment the rndis request succeeds and subchannels start to
> appear. netvsc_sc_open() does unconditional nvscdev->num_sc_offered-- and
> it becomes U32_MAX-1. Consequent rndis_filter_device_remove() will hang
> while waiting for all U32_MAX-1 subchannels to appear and this is not
> going to happen.
> 
> The immediate issue could be solved by adding num_sc_offered > 0 check to
> netvsc_sc_open() but we're getting out of sync with the host and it's not
> easy to adjust things later, e.g. in this particular case we'll be creating
> queues without a user request for it and races are expected. Same applies
> to other parts of the driver which have the same completion timeout.
> 
> Following the trend in drivers/hv/* code I suggest we remove all these
> timeouts completely. As a guest we can always trust the host we're running
> on and if the host screws things up there is no easy way to recover anyway.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Acked-by: Haiyang Zhang <haiyangz@...rosoft.com>

Applied.