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, 12 insertions, 0 deletions

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 474792b825d..7fc5606e6ea 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -391,6 +391,18 @@ extern struct bio *bio_copy_kern(struct request_queue *, void *, unsigned int,
                                  gfp_t, int);
 extern void bio_set_pages_dirty(struct bio *bio);
 extern void bio_check_pages_dirty(struct bio *bio);
+
+#ifndef ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
+# error "You should define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE for your platform"
+#endif
+#if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
+extern void bio_flush_dcache_pages(struct bio *bi);
+#else
+static inline void bio_flush_dcache_pages(struct bio *bi)
+{
+}
+#endif
+
 extern struct bio *bio_copy_user(struct request_queue *, struct rq_map_data *,
                                  unsigned long, unsigned int, int, gfp_t);
 extern struct bio *bio_copy_user_iov(struct request_queue *,