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

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Date:	Wed, 28 Jan 2009 13:52:15 -0800
From:	Roland Dreier <rdreier@...co.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
	general@...ts.openfabrics.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.

 > They all look like lurking (and untested) bug paths. mv643xx is especially
 > bad since it can leak skb. But it should be possible to call pull_tail
 > if bh is disabled (as long as irqs are enabled).

Yes.  The only obvious problem with __pskb_pull_tail() with BHs disabled
is that with CONFIG_HIGHMEM set, it goes into kmap_skb_frag(), which
then unconditionally does local_bh_disable()/local_bh_enable().  There's
no reason in principle that kmap_skb_frag() couldn't do
local_save_flags()/local_restore_flags() instead.

Just grepping around I see other potential issues related to this, for
example the (unused but exported) function fcoe_fc_crc() does
kmap_atomic(KM_SKB_DATA_SOFTIRQ) without any particular BH disabling,
which might run into trouble if used in the wrong context...

 - R.
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