[PATCH v2 05/10] svcrdma: Find rmsgp more reliably

Chuck Lever
2015-01-13T16:03:11Z

xdr_start() can return the wrong rmsgp address if an assumption
about how the xdr_buf was constructed changes. When it gets it
wrong, the client receives a reply that has gibberish in the
RPC/RDMA header, preventing it from matching a waiting RPC request.

Instead, make (and document) just one assumption: that the RDMA
header for the client's RPC call is at the start of the first page
in rq_pages.

Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
---

net/sunrpc/xprtrdma/svc_rdma_sendto.c | 18 ++++--------------
1 files changed, 4 insertions(+), 14 deletions(-)

diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
index 7d79897..7de33d1 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
@@ -483,18 +483,6 @@ void svc_rdma_prep_reply_hdr(struct svc_rqst *rqstp)
{
}

-/*
- * Return the start of an xdr buffer.
- */
-static void *xdr_start(struct xdr_buf *xdr)
-{
- return xdr->head[0].iov_base -
- (xdr->len -
- xdr->page_len -
- xdr->tail[0].iov_len -
- xdr->head[0].iov_len);
-}
-
int svc_rdma_sendto(struct svc_rqst *rqstp)
{
struct svc_xprt *xprt = rqstp->rq_xprt;
@@ -512,8 +500,10 @@ int svc_rdma_sendto(struct svc_rqst *rqstp)

dprintk("svcrdma: sending response for rqstp=%p\n", rqstp);

- /* Get the RDMA request header. */
- rdma_argp = xdr_start(&rqstp->rq_arg);
+ /* Get the RDMA request header. The receive logic always
+ * places this at the start of page 0.
+ */
+ rdma_argp = page_address(rqstp->rq_pages[0]);

/* Build an req vec for the XDR */
ctxt = svc_rdma_get_context(rdma);

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