netdev - Re: [RFC][PATCH] usbnet: Fix tx_bytes statistic running backward in cdc

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Message-ID: <87h9u73eh0.fsf@nemi.mork.no>
Date:	Fri, 27 Feb 2015 10:12:27 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	Ben Hutchings <ben.hutchings@...ethink.co.uk>
Cc:	Oliver Neukum <oliver@...kum.org>, netdev@...r.kernel.org,
	ct-linux-kernel <linux-kernel@...ethink.co.uk>,
	linux-usb@...r.kernel.org, Sami Farin <hvtaifwkbgefbaei@...il.com>,
	Aleksander Morgado <aleksander@...ksander.es>
Subject: Re: [RFC][PATCH] usbnet: Fix tx_bytes statistic running backward in cdc_ncm

Ben Hutchings <ben.hutchings@...ethink.co.uk> writes:

> cdc_ncm disagrees with usbnet about how much framing overhead should
> be counted in the tx_bytes statistics, and tries 'fix' this by
> decrementing tx_bytes on the transmit path.  But statistics must never
> be decremented except due to roll-over; this will thoroughly confuse
> user-space.  Also, tx_bytes is only incremented by usbnet in the
> completion path.
>
> Fix this by requiring drivers that set FLAG_MULTI_FRAME to set a
> tx_bytes delta along with the tx_packets count.
>
> Signed-off-by: Ben Hutchings <ben.hutchings@...ethink.co.uk>
> ---
> I noticed this bug while trying to fix the tx_packets statistic in asix.
> It depends on the patch I just sent for that.  I don't have any hardware
> to test this with, or any need to make it work.  If you want this fix,
> please test and re-submit it yoursef.

I tested this on an MBIM device, and it worked perfectly as-is.  Please
submit it without the RFC prefix.  This fixes a real and reported
problem with the cdc_ncm driver, so I'd claim it's "net" material along
with a stable Cc and

Fixes: beeecd42c3b4 ("net: cdc_ncm/cdc_mbim: adding NCM protocol statistics")

But you and David decide that, of course...


Fixing this was actually on my TODO-list after a recent report showing
one of the problems with the previous hack: The decremented tx_bytes
counter was never corrected if the URB transmission failed, possibly
ending up with a negative (i.e. very large since it is unsigned)
tx_bytes counter.

Thanks a lot.  I didn't know how to do this without introducing a new
callback or something.  Your solutions is very nice, and so obvious when
I see it.  Just brilliant :-)

Tested-by: Bjørn Mork <bjorn@...k.no>

And you might also want (if this is OK for Sami):

Reported-by: Sami Farin <hvtaifwkbgefbaei@...il.com>


Sami wrote:

> I have this USB ID 12d1:157d, Sonera Opengate LTE.
> It says all is okay but no packets are moving.
..
> ifconfig
> wwp3s0u1c2: flags=4291<UP,BROADCAST,RUNNING,NOARP,MULTICAST>  mtu 1500
>         inet 46.132.188.224  netmask 255.255.255.192  broadcast 46.132.188.255
>         inet6 fe80::  prefixlen 64  scopeid 0x20<link>
>         ether 32:35:3a:64:2e:25  txqueuelen 1000  (Ethernet)
>         RX packets 0  bytes 0 (0.0 B)
>         RX errors 17764  dropped 0  overruns 0  frame 0
>         TX packets 6714  bytes 18446744073709268911 (1638.3 PiB)
>         TX errors 1427  dropped 0 overruns 0  carrier 0  collisions 0
>




Bjørn
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