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

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Message-ID: <1309896940.2545.34.camel@edumazet-laptop>
Date:	Tue, 05 Jul 2011 22:15:40 +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 22:02 +0200, Eric Dumazet a écrit :
> Le mardi 05 juillet 2011 à 15:53 -0400, Neil Horman a écrit :
> > I think this is a goo idea, at least for testing.  It seems odd to me that we
> > have the B44_DMARX_PTR value which indicates (ostensibly) the pointer to the
> > descriptor to be processed next (the documentation isnt' very verbose on the
> > subject), along with the EOT bit on a descriptor.  It seems like both the
> > register and the bit are capable of conveying the same (or at least overlapping)
> > information.
> > 
> > I think what I'm having the most trouble with is understanding when the hw looks
> > at the EOT bit in the descriptor.  If it completes a DMA and sees the EOT bit
> > set, does the next DMA occur to the descriptor pointed to by the DMARX_ADDR
> > register?  Of does it stall until such time as the DMARX_PTR register is rotated
> > around?  What if it doesn't see the EOT bit set?  Does it just keep going with
> > the next descriptor?  

Since there is no OWN bit (at least not on the online doc I got : it
says the rx_ring is read only by the NIC), I would say we really need to
advance DMARX_PTR to signal NIC a new entry is available for following
incoming frames.

This is the reason rx_pending max value is B44_RX_RING_SIZE - 1, or else
chip could loop on a circular rx_ring.




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