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Date:	Fri, 30 Jul 2010 09:19:40 -0600
From:	Chris Friesen <>
	Linux Kernel Mailing List <>,
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?



Chris Friesen
Software Developer
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