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

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Message-ID: <20150221183209.GA30167@breakpoint.cc>
Date:	Sat, 21 Feb 2015 19:32:09 +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:
> On Sat, 2015-02-21 at 18:46 +0100, Florian Westphal wrote:
> > 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);
> 
> Note this 'kick' does not provide tail ptr.
> 
> NIC basically looks at TX descriptors to find ones with the DescOwn bit
> set. It stops when if find one TX descriptor _without_ DescOwn.

Makes sense, thanks for explaining this.
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