netdev - Re: [PATCH net-next 2/2] geneve: break dependency to network drivers

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Date:	Wed, 6 Jan 2016 22:18:19 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Jesse Gross <jesse@...nel.org>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 2/2] geneve: break dependency to network drivers

On 06.01.2016 22:01, Jesse Gross wrote:
> On Wed, Jan 6, 2016 at 12:25 PM, Hannes Frederic Sowa
> <hannes@...essinduktion.org> wrote:
>> The refreshes from each module are completely synchronous and don't get
>> interleaved, so as long as the driver is correctly handling the locking
>> internally rtnl lock shouldn't be needed. But as I don't know too much about
>> driver developing I can revisit this.
>>
>> As a advantage I see that the driver developers don't need to worry about
>> the rtnl lock at all when adding new events. Is this realistic?
>
> I don't think that there is much savings to be had by avoiding RTNL
> since the majority of interactions that the driver has with the stack
> involve holding it anyways.
>
> In order to do this safely without RTNL we need to have a lock in each
> driver. I don't think that this is safely handled in all cases today
> and is likely to get worse in the future. I also noticed that Geneve
> actually doesn't hold any special lock while calling into drivers from
> geneve_get_rx_port() so it is de-facto relying on RTNL. All other
> operations in the Geneve driver are protected by RTNL currently, so we
> would need to introduce a new lock to handle this as well. In effect,
> it seems like people are implicitly assuming that these operations are
> covered by RTNL since most similar things are.

Okay, on top of the v1 version I will check all drivers and add 
necessary rtnl_locks. Hopefully it works out and I don't have to defer 
calls into working queues in the drivers first.

Thanks,
Hannes

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