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Date:	Fri, 30 Jul 2010 09:19:40 -0600
From:	Chris Friesen <chris.friesen@...band.com>
To:	netdev@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	davem@...emloft.net
Subject: where are the memory barriers in net driver rx DMA operations?


Documentation/DMA-API-HOWTO.txt says that memory barriers are still
required when accessing consistent mappings.  The example they give is
for reordering stores to consistent memory but I assume this also
applies to reordering loads.

However, I see many net drivers accessing the descriptor ring (in
consistent memory), checking the status bit for the buffer, then calling
dma_unmap_single() and accessing the data without any explicit memory
barrier.  Does the unmapping call act as a barrier in this case?

Thanks,

Chris

-- 
Chris Friesen
Software Developer
GENBAND
chris.friesen@...band.com
www.genband.com
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