block: add helpers to run flush_dcache_page() against a bio and a request's pages

Mtdblock driver doesn't call flush_dcache_page for pages in request.  So,
this causes problems on architectures where the icache doesn't fill from
the dcache or with dcache aliases.  The patch fixes this.

The ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE symbol was introduced to avoid
pointless empty cache-thrashing loops on architectures for which
flush_dcache_page() is a no-op.  Every architecture was provided with this
flush pages on architectires where ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE is
equal 1 or do nothing otherwise.

See "fix mtd_blkdevs problem with caches on some architectures" discussion
on LKML for more information.

Signed-off-by: Ilya Loginov <isloginov@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Peter Horton <phorton@bitbox.co.uk>
Cc: "Ed L. Cashin" <ecashin@coraid.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index 8ca17a3e96ea..64e2b379a350 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -59,12 +59,14 @@ static int do_blktrans_request(struct mtd_blktrans_ops *tr,
                 for (; nsect > 0; nsect--, block++, buf += tr->blksize)
                         if (tr->readsect(dev, block, buf))
                                 return -EIO;
+                rq_flush_dcache_pages(req);
                 return 0;
 
         case WRITE:
                 if (!tr->writesect)
                         return -EIO;
 
+                rq_flush_dcache_pages(req);
                 for (; nsect > 0; nsect--, block++, buf += tr->blksize)
                         if (tr->writesect(dev, block, buf))
                                 return -EIO;