netdev - Re: [PATCH v2 3/3] ucc_geth: Fix hangs after switching from full to half duplex

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Date:	Thu, 10 Sep 2009 23:40:53 +0400
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	Scott Wood <scottwood@...escale.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	Andy Fleming <afleming@...escale.com>,
	Timur Tabi <timur@...escale.com>, linuxppc-dev@...abs.org
Subject: Re: [PATCH v2 3/3] ucc_geth: Fix hangs after switching from full
 to	half duplex

On Thu, Sep 10, 2009 at 01:04:32PM -0500, Scott Wood wrote:
> Anton Vorontsov wrote:
> >MPC8360 QE UCC ethernet controllers hang when changing link duplex
> >under a load (a bit of NFS activity is enough).
> >
> >  PHY: mdio@...02120:00 - Link is Up - 1000/Full
> >  sh-3.00# ethtool -s eth0 speed 100 duplex half autoneg off
> >  PHY: mdio@...02120:00 - Link is Down
> >  PHY: mdio@...02120:00 - Link is Up - 100/Half
> >  NETDEV WATCHDOG: eth0 (ucc_geth): transmit queue 0 timed out
> >  ------------[ cut here ]------------
> >  Badness at c01fcbd0 [verbose debug info unavailable]
> >  NIP: c01fcbd0 LR: c01fcbd0 CTR: c0194e44
> >  ...
> >
> >The cure is to disable the controller before changing speed/duplex
> >and enable it afterwards.
> >
> >Since ugeth_graceful_stop_{tx,rx} now may be called from an atomic
> >context, switch the two functions from msleep() to mdelay().
> 
> Ouch.

Yeah, right... delaying for 10ms with irqs off isn't good.

> Can we put this in a workqueue or something?

adjust_link() itself isn't called from an atomic context.

It's we are grabbing ugeth->lock, i.e. a spinlock. I don't see
why the lock is needed in adjust_link() in its current form,
but if we're going to disable the controller for some time,
we'll have to make sure that no start_xmit() or NAPI is running,
scheduled or will be scheduled until we say so.

I think that lock-less, and thus completely sleep-able variant
of adjust_link is doable.

Thanks,

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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