Patch "xprtrdma: Fix Read chunk padding" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

xprtrdma: Fix Read chunk padding

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
xprtrdma-fix-read-chunk-padding.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Chuck Lever <[email protected]>
Date: Wed, 8 Feb 2017 16:59:46 -0500
Subject: xprtrdma: Fix Read chunk padding

From: Chuck Lever <[email protected]>

commit 24abdf1be15c478e2821d6fc903a4a4440beff02 upstream.

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.

---
 net/sunrpc/xprtrdma/rpc_rdma.c |   10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

@@ -226,8 +226,10 @@ rpcrdma_convert_iovs(struct xdr_buf *xdr
 	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 *xdr
 		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;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/xprtrdma-disable-pad-optimization-by-default.patch queue-4.9/xprtrdma-fix-read-chunk-padding.patch queue-4.9/xprtrdma-reduce-required-number-of-send-sges.patch queue-4.9/nfsd-special-case-truncates-some-more.patch queue-4.9/xprtrdma-per-connection-pad-optimization.patch