netdev - Re: [[net-next] lo uses DEPRECATED zero tx_queue_len - convert driver to use IFF_NO

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Message-ID: <20150826110352.GA28613@orbit.nwl.cc>
Date:	Wed, 26 Aug 2015 13:03:52 +0200
From:	Phil Sutter <phil@....cc>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	"David S. Miller" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [[net-next] lo uses DEPRECATED zero tx_queue_len - convert
 driver to use IFF_NO_QUEUE instead

Hi Geert,

On Wed, Aug 26, 2015 at 12:16:47PM +0200, Geert Uytterhoeven wrote:
> On Wed, Aug 26, 2015 at 11:34 AM, Phil Sutter <phil@....cc> wrote:
> > On Tue, Aug 25, 2015 at 01:16:41PM +0200, Geert Uytterhoeven wrote:
> >> I don't know if this was reported before (I'm not subscribed to netdev), but
> >> Google couldn't find it:
> >>
> >> lo uses DEPRECATED zero tx_queue_len - convert driver to use
> >> IFF_NO_QUEUE instead
> >
> > This is fixed by commit e65db2b ("net: loopback: convert to using
> > IFF_NO_QUEUE"), part of a bigger series converting drivers (see here:
> > http://lists.openwall.net/netdev/2015/08/18/52).
> 
> Strange, that commit is included in my tree, which is based on
> https://git.kernel.org/cgit/linux/kernel/git/geert/renesas-drivers.git/
> and includes net-next?

I'm sorry, the above statement was too quickly put. Florian Westphal
confirmed the problem you are seeing privately, and I can follow from
looking at the code. Obviously I failed to notice that by using
alloc_netdev instead of alloc_etherdev, there is a way for drivers to
circumvent ether_setup completely which leaves tx_queue_len
uninitialized (i.e., 0) and therefore triggers the warning.

I'm yet unsure how to properly fix this issue, but moving the check to a
more appropriate place is certainly advisable.

Thanks for pointing this out,

Phil
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