[SCSI] st: fix mdata->page_order handling

dio transfer always resets mdata->page_order to zero. It breaks
high-order pages previously allocated for non-dio transfer.

This patches adds reserved_page_order to st_buffer structure to save
page order for non-dio transfer.

http://bugzilla.kernel.org/show_bug.cgi?id=14563

When enlarge_buffer() allocates 524288 from 0, st uses six-order page
allocation. So mdata->page_order is 6 and frp_seg is 2.

After that, if st uses dio, sgl_map_user_pages() sets
mdata->page_order to 0 for st_do_scsi(). After that, when we call
normalize_buffer(), it frees only free frp_seg * PAGE_SIZE (2 * 4096)
though we should free frp_seg * PAGE_SIZE << 6 (2 * 4096 << 6). So we
see buffer_size is set to 516096 (524288 - 8192).

Reported-by: Joachim Breuer <linux-kernel@jmbreuer.net>
Tested-by: Joachim Breuer <linux-kernel@jmbreuer.net>
Acked-by: Kai Makisara <kai.makisara@kolumbus.fi>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: stable@kernel.org
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/scsi/st.h b/drivers/scsi/st.h
index 544dc6b1f548..f91a67c6d968 100644
--- a/drivers/scsi/st.h
+++ b/drivers/scsi/st.h
@@ -46,6 +46,7 @@ struct st_buffer {
         struct st_request *last_SRpnt;
         struct st_cmdstatus cmdstat;
         struct page **reserved_pages;
+        int reserved_page_order;
         struct page **mapped_pages;
         struct rq_map_data map_data;
         unsigned char *b_data;