Patch "svcrdma: Change maximum server payload back to RPCSVC_MAXPAYLOAD" has been added to the 4.2-stable tree

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

svcrdma: Change maximum server payload back to RPCSVC_MAXPAYLOAD

to the 4.2-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:
svcrdma-change-maximum-server-payload-back-to-rpcsvc_maxpayload.patch
and it can be found in the queue-4.2 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: Fri, 7 Aug 2015 16:55:46 -0400
Subject: svcrdma: Change maximum server payload back to RPCSVC_MAXPAYLOAD

From: Chuck Lever <[email protected]>

commit cc9a903d915c21626b6b2fbf8ed0ff16a7f82210 upstream.

Both commit 0380a3f375 ("svcrdma: Add a separate "max data segs" macro for svcrdma") and commit 7e5be28827bf ("svcrdma: advertise the correct max payload") are incorrect. This commit reverts both changes, restoring the server's maximum payload size to 1MB.

Commit 7e5be28827bf based the server's maximum payload on the _client's_ RPCRDMA_MAX_DATA_SEGS value. That was wrong.

Commit 0380a3f375 tried to fix this so that the client maximum payload size could be raised without affecting the server, but managed to confuse matters more on the server side.

More importantly, limiting the advertised maximum payload size was meant to be a workaround, not the actual fix. We need to revisit

https://bugzilla.linux-nfs.org/show_bug.cgi?id=270

A Linux client on a platform with 64KB pages can overrun and crash an x86_64 NFS/RDMA server when the r/wsize is 1MB. An x86/64 Linux client seems to work fine using 1MB reads and writes when the Linux server's maximum payload size is restored to 1MB.

---
 include/linux/sunrpc/svc_rdma.h          |    9 ++-------
 net/sunrpc/xprtrdma/svc_rdma_transport.c |    2 +-
 net/sunrpc/xprtrdma/xprt_rdma.h          |    1 -
 3 files changed, 3 insertions(+), 9 deletions(-)

@@ -172,13 +172,6 @@ struct svcxprt_rdma {
 #define RDMAXPRT_SQ_PENDING	2
 #define RDMAXPRT_CONN_PENDING	3
 
-#define RPCRDMA_MAX_SVC_SEGS	(64)	/* server max scatter/gather */
-#if RPCSVC_MAXPAYLOAD < (RPCRDMA_MAX_SVC_SEGS << PAGE_SHIFT)
-#define RPCRDMA_MAXPAYLOAD	RPCSVC_MAXPAYLOAD
-#else
-#define RPCRDMA_MAXPAYLOAD	(RPCRDMA_MAX_SVC_SEGS << PAGE_SHIFT)
-#endif
-
 #define RPCRDMA_LISTEN_BACKLOG  10
 /* The default ORD value is based on two outstanding full-size writes with a
  * page size of 4k, or 32k * 2 ops / 4k = 16 outstanding RDMA_READ.  */

@@ -187,6 +180,8 @@ struct svcxprt_rdma {
 #define RPCRDMA_MAX_REQUESTS    32
 #define RPCRDMA_MAX_REQ_SIZE    4096
 
+#define RPCSVC_MAXPAYLOAD_RDMA	RPCSVC_MAXPAYLOAD
+
 /* svc_rdma_marshal.c */
 extern int svc_rdma_xdr_decode_req(struct rpcrdma_msg **, struct svc_rqst *);
 extern int svc_rdma_xdr_encode_error(struct svcxprt_rdma *,

@@ -91,7 +91,7 @@ struct svc_xprt_class svc_rdma_class = {
 	.xcl_name = "rdma",
 	.xcl_owner = THIS_MODULE,
 	.xcl_ops = &svc_rdma_ops,
-	.xcl_max_payload = RPCRDMA_MAXPAYLOAD,
+	.xcl_max_payload = RPCSVC_MAXPAYLOAD_RDMA,
 	.xcl_ident = XPRT_TRANSPORT_RDMA,
 };
 

@@ -51,7 +51,6 @@
 #include <linux/sunrpc/clnt.h> 		/* rpc_xprt */
 #include <linux/sunrpc/rpc_rdma.h> 	/* RPC/RDMA protocol */
 #include <linux/sunrpc/xprtrdma.h> 	/* xprt parameters */
-#include <linux/sunrpc/svc.h>		/* RPCSVC_MAXPAYLOAD */
 
 #define RDMA_RESOLVE_TIMEOUT	(5000)	/* 5 seconds */
 #define RDMA_CONNECT_RETRY_MAX	(2)	/* retries if no listener backlog */

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

queue-4.2/svcrdma-change-maximum-server-payload-back-to-rpcsvc_maxpayload.patch queue-4.2/nfs-don-t-let-the-ctime-override-attribute-barriers.patch