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

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Date:	Tue, 05 Jul 2011 20:32:55 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	Alexey Zaytsev <alexey.zaytsev@...il.com>,
	Michael Büsch <m@...s.ch>,
	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 mardi 05 juillet 2011 à 20:13 +0200, Eric Dumazet a écrit :
> Le mardi 05 juillet 2011 à 14:06 -0400, Neil Horman a écrit :
> > On Tue, Jul 05, 2011 at 06:47:21PM +0200, Eric Dumazet wrote:
> > > Le mardi 05 juillet 2011 à 12:42 -0400, Neil Horman a écrit :
> > > > On Tue, Jul 05, 2011 at 06:12:32PM +0200, Eric Dumazet wrote:
> > > 
> > > > > So all descriptors before prod are guaranteed to be ready for host
> > > > > consume... Fact that a dma access is running on 'next descriptor' should
> > > > > be irrelevant.
> > > > > 
> > > > But we handle more than one descriptor per b44_rx call - theres a while loop in
> > > > there where we do advance to the next descriptor.
> > > 
> > > Yes, but we advance up to 'prod', which is the very last safe
> > > descriptor.
> > > 
> > > If hardware advertises descriptor X being ready to be handled by host,
> > > while DMA on this X descriptor is not yet finished, this would be a
> > > really useless hardware ;)
> > > 
> > > 
> > > 
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe netdev" in
> > > the body of a message to majordomo@...r.kernel.org
> > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > > 
> > 
> > 
> > Something else just jumped out at me.  During b44_open, we call b44_init_rings.
> > This function allocates bp->rx_pending skb's and iteratively puts them in the rx
> > dma ring. bp->rx_pending is initalized to B44_DEF_RX_RING_PENDING, which is
> > defined as 200 (just about half of the 512 entries that the dma ring actually
> > supports in the hardware.  This is normally ok, as subsequent calls to
> > b44_alloc_rx_skb will fill in entries in the ring as those skbs are consumed.
> > The problem with this however is that b44_alloc_rx_skb only sets the
> > DESC_CTRL_EOT bit in the descriptor of the 512th entry, indicating that the
> > hardware should wrap around and reset the index counter.  If a large volume of
> > traffic is pushed through the adapter early on after initalization, or if the
> > cpu is busy during init, it would be possible that the ring buffer would fill up
> > prior to having additional entries added to the ring, the result being that the
> > dma engine would reach the end of the allocated descriptors, not see an EOT bit
> > set, and continue on using unallocated descriptors.
> > 
> > Just a theory, but it would be interesting to see if the problem subsided if you
> > ensured that you allocated  a full descriptor ring on b44_open
> > Neil
> >  
> > diff --git a/drivers/net/b44.c b/drivers/net/b44.c
> > index 3d247f3..1b58a7c 100644
> > --- a/drivers/net/b44.c
> > +++ b/drivers/net/b44.c
> > @@ -57,7 +57,7 @@
> >  #define B44_MAX_MTU			1500
> >  
> >  #define B44_RX_RING_SIZE		512
> > -#define B44_DEF_RX_RING_PENDING		200
> > +#define B44_DEF_RX_RING_PENDING		512
> >  #define B44_RX_RING_BYTES	(sizeof(struct dma_desc) * \
> >  				 B44_RX_RING_SIZE)
> >  #define B44_TX_RING_SIZE		512
> 
> No
> 
> Please take time to read the driver again.
> 
> 200 desc are setup, and NIC is not allowed to use more than 200 descs.
> 
> ( B44_DMARX_PTR )
> 
> We carefuly advance this pointer after a new desc(s) is(are) setup
> 
> 

Then, maybe the driver model is completely wrong, and should really
setup 512 buffers, or use less descs but set EOT on last one.

Currently it uses a 200 sliding window out of the 512 descs.



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