linux-kernel - Re: [PATCH net-next 1/2] net: mvneta: add xmit

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Message-ID: <1473777748.18970.120.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Tue, 13 Sep 2016 07:42:28 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Marcin Wojtas <mw@...ihalf.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        netdev@...r.kernel.org, davem@...emloft.net,
        linux@....linux.org.uk, sebastian.hesselbarth@...il.com,
        andrew@...n.ch, jason@...edaemon.net,
        thomas.petazzoni@...e-electrons.com,
        gregory.clement@...e-electrons.com, nadavh@...vell.com,
        alior@...vell.com, simon.guinot@...uanux.org, nitroshift@...oo.com,
        jaz@...ihalf.com
Subject: Re: [PATCH net-next 1/2] net: mvneta: add xmit_more support

On Tue, 2016-09-13 at 07:33 -0700, Eric Dumazet wrote:

> Hi Marcin
> 
> Well, given the above comment, and fact that MVNETA_MAX_TXD == 532, it
> looks like you might add a bug if more than 256 skb are given to your
> ndo_start_xmit() with skb->xmit_more = 1
> 
> I therefore suggest you make sure it does not happen.
> 
> txq->pending += frags;
> if (!skb->xmit_more ||
>     txq->pending > 256 - MVNETA_MAX_SKB_DESCS ||
>     netif_xmit_stopped(nq))
> 	mvneta_txq_pend_desc_add(pp, txq)
> 

Another solution would be to test the potential overflow in mvneta_tx()
and force a mvneta_txq_pend_desc_add(pp, txq) _before_ adding the desc
of the "about to be cooked" TSO packet.

(This is because MVNETA_MAX_SKB_DESCS is 217, so 255-217 leaves few room
for xmit_more to show its power)