Patch "xprtrdma: Disable pad optimization by default" has been added to the 4.10-stable tree

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

xprtrdma: Disable pad optimization by default

to the 4.10-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-disable-pad-optimization-by-default.patch
and it can be found in the queue-4.10 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 17:00:02 -0500
Subject: xprtrdma: Disable pad optimization by default

From: Chuck Lever <[email protected]>

commit c95a3c6b88658bcb8f77f85f31a0b9d9036e8016 upstream.

Commit d5440e27d3e5 ("xprtrdma: Enable pad optimization") made the Linux client omit XDR round-up padding in normal Read and Write chunks so that the client doesn't have to register and invalidate 3-byte memory regions that contain no real data.

Unfortunately, my cheery 2014 assessment that this optimization "is supported now by both Linux and Solaris servers" was premature. We've found bugs in Solaris in this area since commit d5440e27d3e5 ("xprtrdma: Enable pad optimization") was merged (SYMLINK is the main offender).

So for maximum interoperability, I'm disabling this optimization again. If a CM private message is exchanged when connecting, the client recognizes that the server is Linux, and enables the optimization for that connection.

Until now the Solaris server bugs did not impact common operations, and were thus largely benign. Soon, less capable devices on Linux NFS/RDMA clients will make use of Read chunks more often, and these Solaris bugs will prevent interoperation in more cases.

---
 net/sunrpc/xprtrdma/transport.c |    2 +-
 net/sunrpc/xprtrdma/verbs.c     |    1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

@@ -67,7 +67,7 @@ unsigned int xprt_rdma_max_inline_read =
 static unsigned int xprt_rdma_max_inline_write = RPCRDMA_DEF_INLINE;
 static unsigned int xprt_rdma_inline_write_padding;
 static unsigned int xprt_rdma_memreg_strategy = RPCRDMA_FRMR;
-		int xprt_rdma_pad_optimize = 1;
+		int xprt_rdma_pad_optimize = 0;
 
 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
 

@@ -216,6 +216,7 @@ rpcrdma_update_connect_private(struct rp
 	    pmsg->cp_magic == rpcrdma_cmp_magic &&
 	    pmsg->cp_version == RPCRDMA_CMP_VERSION) {
 		r_xprt->rx_ia.ri_reminv_expected = true;
+		r_xprt->rx_ia.ri_implicit_roundup = true;
 		rsize = rpcrdma_decode_buffer_size(pmsg->cp_send_size);
 		wsize = rpcrdma_decode_buffer_size(pmsg->cp_recv_size);
 	}

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

queue-4.10/xprtrdma-disable-pad-optimization-by-default.patch queue-4.10/xprtrdma-fix-read-chunk-padding.patch queue-4.10/xprtrdma-reduce-required-number-of-send-sges.patch queue-4.10/nfsd-special-case-truncates-some-more.patch queue-4.10/xprtrdma-per-connection-pad-optimization.patch