netdev - Re: [PATCH] gianfar: Fix crashes on RX path

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Date:	Tue, 26 Oct 2010 23:20:42 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, eminak71@...il.com,
	akpm@...ux-foundation.org, netdev@...r.kernel.org,
	bugzilla-daemon@...zilla.kernel.org,
	bugme-daemon@...zilla.kernel.org, avorontsov@...sta.com,
	afleming@...escale.com
Subject: Re: [PATCH] gianfar: Fix crashes on RX path

On Tue, Oct 26, 2010 at 10:42:57AM -0700, David Miller wrote:
> From: Jarek Poplawski <jarkao2@...il.com>
> Date: Fri, 22 Oct 2010 08:52:48 +0000
> 
> > On Fri, Oct 22, 2010 at 06:52:31AM +0000, Jarek Poplawski wrote:
> >> On Fri, Oct 22, 2010 at 08:11:57AM +0200, Eric Dumazet wrote:
> > ...
> >> > Gianfar claims to be multiqueue, but only one cpu can run gfar_poll()
> >> > and call gfar_clean_tx_ring() / gfar_clean_rx_ring()
> >> > 
> >> > If not, there would be more bugs than only rx_recycle thing
> >> 
> >> I didn't find what prevents running gfar_poll on many cpus and don't
> >> claim there is no more bugs around.
> > 
> > On the other hand, I don't see your point in the code below either.
> > These're only per gfargrp queues - not per device, aren't they?
> 
> I am still not at the point where I feel confortable applying this bug
> fix, in fact I am very far from that.
> 
> None of the logic is consistent in what we are saying causes the
> problem.
> 
> Anything that would make the RX recycling code racy and corrupt
> recycling queue of the gianfar driver, would also corrupt all of the
> other RX side and other driver state.
> 
> The NAPI state is unary for gianfar, and inside of that singular
> ->poll() instance it iterates over the queues.

IMHO, the NAPI state is unary only for gfargrp, and multiple ->poll()
instances share a (unary) rx_recycle queue without proper locking.

Thanks,
Jarek P.
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