xprtrdma: Fix Read chunk padding

When pad optimization is disabled, rpcrdma_convert_iovs still
does not add explicit XDR round-up padding to a Read chunk.

Commit 677eb17e94ed ("xprtrdma: Fix XDR tail buffer marshalling")
incorrectly short-circuited the test for whether round-up padding
is needed that appears later in rpcrdma_convert_iovs.

However, if this is indeed a regular Read chunk (and not a
Position-Zero Read chunk), the tail iovec _always_ contains the
chunk's padding, and never anything else.

So, it's easy to just skip the tail when padding optimization is
enabled, and add the tail in a subsequent Read chunk segment, if
disabled.

Fixes: 677eb17e94ed ("xprtrdma: Fix XDR tail buffer marshalling")
Cc: stable@vger.kernel.org # v4.9+
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

1 files changed, 4 insertions, 6 deletions

diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
index c52e0f2ffe52..a524d3c2e8ac 100644
--- a/net/sunrpc/xprtrdma/rpc_rdma.c
+++ b/net/sunrpc/xprtrdma/rpc_rdma.c
@@ -226,8 +226,10 @@ rpcrdma_convert_iovs(struct xdr_buf *xdrbuf, unsigned int pos,
         if (len && n == RPCRDMA_MAX_SEGS)
                 goto out_overflow;
 
-        /* When encoding the read list, the tail is always sent inline */
-        if (type == rpcrdma_readch)
+        /* When encoding a Read chunk, the tail iovec contains an
+         * XDR pad and may be omitted.
+         */
+        if (type == rpcrdma_readch && xprt_rdma_pad_optimize)
                 return n;
 
         /* When encoding the Write list, some servers need to see an extra
@@ -238,10 +240,6 @@ rpcrdma_convert_iovs(struct xdr_buf *xdrbuf, unsigned int pos,
                 return n;
 
         if (xdrbuf->tail[0].iov_len) {
-                /* the rpcrdma protocol allows us to omit any trailing
-                 * xdr pad bytes, saving the server an RDMA operation. */
-                if (xdrbuf->tail[0].iov_len < 4 && xprt_rdma_pad_optimize)
-                        return n;
                 n = rpcrdma_convert_kvec(&xdrbuf->tail[0], seg, n);
                 if (n == RPCRDMA_MAX_SEGS)
                         goto out_overflow;