linux-kernel - Re: [PATCH net-next v2] netvsc: get rid of completion timeouts

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Message-ID: <87eg86agkx.fsf@vitty.brq.redhat.com>
Date:	Thu, 09 Jun 2016 10:53:34 +0200
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, devel@...uxdriverproject.org,
	linux-kernel@...r.kernel.org, kys@...rosoft.com,
	haiyangz@...rosoft.com
Subject: Re: [PATCH net-next v2] netvsc: get rid of completion timeouts

David Miller <davem@...emloft.net> writes:

> From: Vitaly Kuznetsov <vkuznets@...hat.com>
> Date: Wed,  8 Jun 2016 19:17:41 +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>
>
> This doesn't apply cleanly to net-next, I get rejects.

Sorry for the screw up, apparently I forgot about my own cleanups I sent
before. v3 is coming.

-- 
  Vitaly