Date: Sat, 21 Feb 2015 18:46:25 +0100
From: Florian Westphal <fw@strlen.de>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Florian Westphal <fw@strlen.de>, Tomas Szepe <szepe@pinerecords.com>,
        Francois Romieu <romieu@fr.zoreil.com>,
        Hayes Wang <hayeswang@realtek.com>, Eric Dumazet <edumazet@google.com>,
        Tom Herbert <therbert@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Marco Berizzi <pupilla@hotmail.com>, linux-kernel@vger.kernel.org,
        netdev <netdev@vger.kernel.org>
Subject: Re: 1e918876 breaks r8169 (linux-3.18+)
Message-ID: <20150221174625.GA29681@breakpoint.cc>
References: <20150203100816.GA5807@louise.pinerecords.com>
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 <20150210154536.GB16264@breakpoint.cc>
 <20150221101512.GB17223@louise.pinerecords.com>
 <20150221103104.GA26574@breakpoint.cc>
 <1424535746.5565.42.camel@edumazet-glaptop2.roam.corp.google.com>
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Eric Dumazet <eric.dumazet@gmail.com> wrote:
> Hold on.
> 
> I believe there is one race in the way you access skb->xmit_more _after_
> 
> txd->opts1 = cpu_to_le32(status);
> 
> After this point, TX might have completed and TX completion already have
> freed skb

Hmm, I _thought_ HW would not start xmit of this descriptor/skb until after

RTL_W8(TxPoll, NPQ);

call a bit later... your patch surely looks safer though, thanks for
looking into this.

> Could Tomas try following fix ?

In addition -- Tomas, on your affected board -- did you try
turning off gso/tso?

Holger Hoffst?tte mentioned on lkml that his affected r8169 nic is
stable with xmit_more+bql after disabling gso/tso on the nic

(ethtool -k $dev to display settings, "-K $dev tso off gso off" to
 disable offloads).
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