netdev - Re: [Bugme-new] [Bug 38102] New: BUG kmalloc-2048: Poison overwritten

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Date:	Wed, 06 Jul 2011 18:35:24 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Michael Büsch <m@...s.ch>
Cc:	Neil Horman <nhorman@...driver.com>,
	Alexey Zaytsev <alexey.zaytsev@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	netdev@...r.kernel.org, Gary Zambrano <zambrano@...adcom.com>,
	bugme-daemon@...zilla.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Pekka Pietikainen <pp@...oulu.fi>,
	Florian Schirmer <jolt@...box.org>,
	Felix Fietkau <nbd@...nwrt.org>, Michael Buesch <mb@...sch.de>
Subject: Re: [Bugme-new] [Bug 38102] New: BUG kmalloc-2048: Poison
 overwritten

Le mercredi 06 juillet 2011 à 18:12 +0200, Michael Büsch a écrit :
> On Wed, 06 Jul 2011 18:00:19 +0200
> Eric Dumazet <eric.dumazet@...il.com> wrote:
> > Not exactly :
> > 
> > If we read one skb at descriptor 0, we prepare a new buffer on slot 200,
> > and advance DMARX_PTR to 201*sizeof(descriptor).
> 
> I don't think so. Why do you think this is the case?
> We allocate a new descriptor buffer for the consumed buffer at exactly
> the same place (which is "cons").
> (Alternatively, we leave the buffer in place, and just copy the data to a new buffer).
> And DMARX_PTR is updated to the last "cons", which is one beyond
> the last buffer that we consumed (and pushed up the net stack).

Not at all.

If it was true, b44_recycle_rx() would not even exist as is.

When we allocate a new buffer, we put it at rx_prod index, which is the
slot _after_ window, not the first slot.

First time we dequeue a packet from NIC, rx_prod is something like 200


Oh, it seems we do the following in b44_init_hw()

bp->rx_prod = bp->rx_pending;

But this seems completely wrong, if b44_init_rings() was not able to
allocate rx_pending buffers (b44_alloc_rx_skb() can return NULL)



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