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>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index c4366c9373c5..dcd9e659ed9d 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -720,7 +720,7 @@ static int set_syndrome_sources(struct page **srcs, struct stripe_head *sh)
         int i;
 
         for (i = 0; i < disks; i++)
-                srcs[i] = (void *)raid6_empty_zero_page;
+                srcs[i] = NULL;
 
         count = 0;
         i = d0_idx;
@@ -816,7 +816,7 @@ ops_run_compute6_2(struct stripe_head *sh, struct raid5_percpu *percpu)
          * slot number conversion for 'faila' and 'failb'
          */
         for (i = 0; i < disks ; i++)
-                blocks[i] = (void *)raid6_empty_zero_page;
+                blocks[i] = NULL;
         count = 0;
         i = d0_idx;
         do {