netdev - Re: [ofa-general] NetEffect, iw

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Date:	Fri, 30 Jan 2009 09:35:52 -0800
From:	Roland Dreier <rdreier@...co.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	davem@...emloft.net, aluno3@...zta.onet.pl,
	general@...ts.openfabrics.org, netdev@...r.kernel.org
Subject: Re: [ofa-general] NetEffect, iw_nes and kernel warning

 > > OK, thanks... what confused me is that several other drivers also do
 > > skb_linearize() in their hard_start_xmit method... eg bnx2x,
 > > via-velocity, mv643xx_eth.  So there are several other lurking bugs to
 > > deal with here I guess.
 > 
 > I don't know about the rest but bnx2x is certainly OK since it
 > only does so with IRQ enabled.  It is legal to call skb_linearize
 > as long as you're sure that IRQs are enabled, which is always the
 > case for hard_start_xmit upon entry.

I don't believe this is accurate.  Calling skb_linearize() (on a kernel
with CONFIG_HIGHMEM set) can end up calling local_bh_enable() in
kunmap_skb_frag(), which can obviously cause problems if the initial
context relies on having BHs disabled (as hard_start_xmit does).

 - R.
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