[PATCH] svcrdma: fix offset calculation for non-page aligned sge entries

[Jeff Layton <jlayton@redhat.com>]

The xdr_off value in dma_map_xdr gets passed to ib_dma_map_page as the
offset into the page to be mapped. For the case of the pages array, the
existing calculation always seems to end up at 0, which causes data
corruption when a non-page-aligned READ request comes in. The server ends
up doing the RDMA_WRITE from the wrong part of the page.

Override the xdr_off value with the page_base in that situation to fix
the issue. Obviously, this method can't contend with a page_base that is
larger than PAGE_SIZE. I'm not sure if that's ever the case, but add a
WARN_ON in the event that that ever happens.

Cc: Tom Tucker <tom@opengridcomputing.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 net/sunrpc/xprtrdma/svc_rdma_sendto.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
index c1d124dc772b..76e524b428d0 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
@@ -265,8 +265,11 @@ static dma_addr_t dma_map_xdr(struct svcxprt_rdma *xprt,
 		xdr_off -= xdr->head[0].iov_len;
 		if (xdr_off < xdr->page_len) {
 			/* This offset is in the page list */
-			page = xdr->pages[xdr_off >> PAGE_SHIFT];
-			xdr_off &= ~PAGE_MASK;
+			int pgnum = xdr_off >> PAGE_SHIFT;
+
+			page = xdr->pages[pgnum];
+			WARN_ON(xdr->page_base > PAGE_SIZE);
+			xdr_off = pgnum ? 0 : xdr->page_base;
 		} else {
 			/* This offset is in the tail */
 			xdr_off -= xdr->page_len;
-- 
1.8.5.3