xprtrdma: Revert 586a0787ce35

Commit 9ed5af268e88 ("SUNRPC: Clean up the handling of page padding
in rpc_prepare_reply_pages()") [Dec 2020] affects RPC Replies that
have a data payload (i.e., Write chunks).

rpcrdma_prepare_readch(), as its name suggests, sets up Read chunks
which are data payloads within RPC Calls. Those payloads are
constructed by xdr_write_pages(), which continues to stuff the call
buffer's tail kvec with the payload's XDR roundup. Thus removing
the tail buffer logic in rpcrdma_prepare_readch() was the wrong
thing to do.

Fixes: 586a0787ce35 ("xprtrdma: Clean up rpcrdma_prepare_readch()")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
index 649f7d8..c335c13 100644 (file)
--- a/net/sunrpc/xprtrdma/rpc_rdma.c
+++ b/net/sunrpc/xprtrdma/rpc_rdma.c
@@ -628,8 +628,9 @@ out_mapping_err:
        return false;
 }
 
-/* The tail iovec might not reside in the same page as the
- * head iovec.
+/* The tail iovec may include an XDR pad for the page list,
+ * as well as additional content, and may not reside in the
+ * same page as the head iovec.
  */
 static bool rpcrdma_prepare_tail_iov(struct rpcrdma_req *req,
                                     struct xdr_buf *xdr,
@@ -747,19 +748,27 @@ static bool rpcrdma_prepare_readch(struct rpcrdma_xprt *r_xprt,
                                   struct rpcrdma_req *req,
                                   struct xdr_buf *xdr)
 {
-       struct kvec *tail = &xdr->tail[0];
-
        if (!rpcrdma_prepare_head_iov(r_xprt, req, xdr->head[0].iov_len))
                return false;
 
-       /* If there is a Read chunk, the page list is handled
+       /* If there is a Read chunk, the page list is being handled
         * via explicit RDMA, and thus is skipped here.
         */
 
-       if (tail->iov_len) {
-               if (!rpcrdma_prepare_tail_iov(req, xdr,
-                                             offset_in_page(tail->iov_base),
-                                             tail->iov_len))
+       /* Do not include the tail if it is only an XDR pad */
+       if (xdr->tail[0].iov_len > 3) {
+               unsigned int page_base, len;
+
+               /* If the content in the page list is an odd length,
+                * xdr_write_pages() adds a pad at the beginning of
+                * the tail iovec. Force the tail's non-pad content to
+                * land at the next XDR position in the Send message.
+                */
+               page_base = offset_in_page(xdr->tail[0].iov_base);
+               len = xdr->tail[0].iov_len;
+               page_base += len & 3;
+               len -= len & 3;
+               if (!rpcrdma_prepare_tail_iov(req, xdr, page_base, len))
                        return false;
                kref_get(&req->rl_kref);
        }