netdev - Re: Stack sends oversize UDP packet to the driver

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Message-Id: <20190122.120937.355805969121598441.davem@davemloft.net>
Date:   Tue, 22 Jan 2019 12:09:37 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     maheshb@...gle.com
Cc:     michael.chan@...adcom.com, dja@...ens.net, netdev@...r.kernel.org,
        edumazet@...gle.com, willemb@...gle.com
Subject: Re: Stack sends oversize UDP packet to the driver

From: Mahesh Bandewar (महेश बंडेवार) <maheshb@...gle.com>
Date: Tue, 22 Jan 2019 10:28:58 -0800

> On Mon, Jan 21, 2019 at 4:59 PM Michael Chan <michael.chan@...adcom.com> wrote:
>>
>> On Mon, Jan 21, 2019 at 4:36 PM Daniel Axtens <dja@...ens.net> wrote:
>>
>> > I hit a similar sounding issue on a bnx2x - see commit
>> > 8914a595110a6eca69a5e275b323f5d09e18f4f9
>> >
>> > In that case, a GSO packet with gso_size too large for the firmware was
>> > coming to the bnx2x driver from an ibmveth device via Open vSwitch. I
>> > also toyed with a fix in the stack and ended up fixing just the driver.
>>
>> Hi Daniel, yes I remember the issue that you reported at that time.
>> The current issue is similar but for non-TSO UDP packets.

I just want to step in and say that I really don't want drivers to have to
deal with this problem, if possible.  Drivers are hard enough to write
already.

However, some aspects of this problem, like the MTU changes, route flaps,
packet mirroring, etc. are all in one way or another asynchonous to the
data fast path and therefore we may end up having to do something like
this afterall right at the last step before ->ndo_start_xmit() or similar.

Just my $0.02