linux-kernel - Re: 1e918876 breaks r8169 (linux-3.18+)

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Message-ID: <20150221174625.GA29681@breakpoint.cc>
Date:	Sat, 21 Feb 2015 18:46:25 +0100
From:	Florian Westphal <fw@...len.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Florian Westphal <fw@...len.de>,
	Tomas Szepe <szepe@...erecords.com>,
	Francois Romieu <romieu@...zoreil.com>,
	Hayes Wang <hayeswang@...ltek.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Tom Herbert <therbert@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Marco Berizzi <pupilla@...mail.com>,
	linux-kernel@...r.kernel.org, netdev <netdev@...r.kernel.org>
Subject: Re: 1e918876 breaks r8169 (linux-3.18+)

Eric Dumazet <eric.dumazet@...il.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 Hoffstätte 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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