From: NeilBrown <neilb@suse.de>
Date: Fri, 16 Oct 2009 05:40:25 +0000 (+1100)
Subject: md/async: don't pass a memory pointer as a page pointer.
X-Git-Tag: v2.6.32-rc6~27^2~5
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5dd33c9a4c29015f6d87568d33521c98931a387e;p=pandora-kernel.git

md/async: don't pass a memory pointer as a page pointer.

md/raid6 passes a list of 'struct page *' to the async_tx routines,
which then either DMA map them for offload, or take the page_address
for CPU based calculations.

For RAID6 we sometime leave 'blanks' in the list of pages.
For CPU based calcs, we want to treat theses as a page of zeros.
For offloaded calculations, we simply don't pass a page to the
hardware.

Currently the 'blanks' are encoded as a pointer to
raid6_empty_zero_page.  This is a 4096 byte memory region, not a
'struct page'.  This is mostly handled correctly but is rather ugly.

So change the code to pass and expect a NULL pointer for the blanks.
When taking page_address of a page, we need to check for a NULL and
in that case use raid6_empty_zero_page.

Signed-off-by: NeilBrown <neilb@suse.de>
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