[PATCH 9/9] sunrpc: use SKB fragment destructors to delay completion until page is released by network stack.

[Ian Campbell <ian.campbell@citrix.com>]

This prevents an issue where an ACK is delayed, a retransmit is queued (either
at the RPC or TCP level) and the ACK arrives before the retransmission hits the
wire. If this happens to an NFS WRITE RPC then the write() system call
completes and the userspace process can continue, potentially modifying data
referenced by the retransmission before the retransmission occurs.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Neil Brown <neilb@suse.de>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: linux-nfs@vger.kernel.org
Cc: netdev@vger.kernel.org
---
 include/linux/sunrpc/xdr.h  |    2 ++
 include/linux/sunrpc/xprt.h |    5 ++++-
 net/sunrpc/clnt.c           |   27 ++++++++++++++++++++++-----
 net/sunrpc/svcsock.c        |    3 ++-
 net/sunrpc/xprt.c           |   12 ++++++++++++
 net/sunrpc/xprtsock.c       |    3 ++-
 6 files changed, 44 insertions(+), 8 deletions(-)

diff --git a/include/linux/sunrpc/xdr.h b/include/linux/sunrpc/xdr.h
index af70af3..ff1b121 100644
--- a/include/linux/sunrpc/xdr.h
+++ b/include/linux/sunrpc/xdr.h
@@ -16,6 +16,7 @@
 #include <asm/byteorder.h>
 #include <asm/unaligned.h>
 #include <linux/scatterlist.h>
+#include <linux/skbuff.h>
 
 /*
  * Buffer adjustment
@@ -57,6 +58,7 @@ struct xdr_buf {
 			tail[1];	/* Appended after page data */
 
 	struct page **	pages;		/* Array of contiguous pages */
+	struct skb_frag_destructor *destructor;
 	unsigned int	page_base,	/* Start of page data */
 			page_len,	/* Length of page data */
 			flags;		/* Flags for data disposition */
diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
index 77d278d..e8d3f18 100644
--- a/include/linux/sunrpc/xprt.h
+++ b/include/linux/sunrpc/xprt.h
@@ -92,7 +92,10 @@ struct rpc_rqst {
 						/* A cookie used to track the
 						   state of the transport
 						   connection */
-	
+	struct skb_frag_destructor destructor;	/* SKB paged fragment
+						 * destructor for
+						 * transmitted pages*/
+
 	/*
 	 * Partial send handling
 	 */
diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 6797246..351bf3d 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -61,6 +61,7 @@ static void	call_reserve(struct rpc_task *task);
 static void	call_reserveresult(struct rpc_task *task);
 static void	call_allocate(struct rpc_task *task);
 static void	call_decode(struct rpc_task *task);
+static void	call_complete(struct rpc_task *task);
 static void	call_bind(struct rpc_task *task);
 static void	call_bind_status(struct rpc_task *task);
 static void	call_transmit(struct rpc_task *task);
@@ -1416,6 +1417,8 @@ rpc_xdr_encode(struct rpc_task *task)
 			 (char *)req->rq_buffer + req->rq_callsize,
 			 req->rq_rcvsize);
 
+	req->rq_snd_buf.destructor = &req->destructor;
+
 	p = rpc_encode_header(task);
 	if (p == NULL) {
 		printk(KERN_INFO "RPC: couldn't encode RPC header, exit EIO\n");
@@ -1581,6 +1584,7 @@ call_connect_status(struct rpc_task *task)
 static void
 call_transmit(struct rpc_task *task)
 {
+	struct rpc_rqst *req = task->tk_rqstp;
 	dprint_status(task);
 
 	task->tk_action = call_status;
@@ -1614,8 +1618,8 @@ call_transmit(struct rpc_task *task)
 	call_transmit_status(task);
 	if (rpc_reply_expected(task))
 		return;
-	task->tk_action = rpc_exit_task;
-	rpc_wake_up_queued_task(&task->tk_xprt->pending, task);
+	task->tk_action = call_complete;
+	skb_frag_destructor_unref(&req->destructor);
 }
 
 /*
@@ -1688,7 +1692,8 @@ call_bc_transmit(struct rpc_task *task)
 		return;
 	}
 
-	task->tk_action = rpc_exit_task;
+	task->tk_action = call_complete;
+	skb_frag_destructor_unref(&req->destructor);
 	if (task->tk_status < 0) {
 		printk(KERN_NOTICE "RPC: Could not send backchannel reply "
 			"error: %d\n", task->tk_status);
@@ -1728,7 +1733,6 @@ call_bc_transmit(struct rpc_task *task)
 			"error: %d\n", task->tk_status);
 		break;
 	}
-	rpc_wake_up_queued_task(&req->rq_xprt->pending, task);
 }
 #endif /* CONFIG_SUNRPC_BACKCHANNEL */
 
@@ -1906,12 +1910,14 @@ call_decode(struct rpc_task *task)
 		return;
 	}
 
-	task->tk_action = rpc_exit_task;
+	task->tk_action = call_complete;
 
 	if (decode) {
 		task->tk_status = rpcauth_unwrap_resp(task, decode, req, p,
 						      task->tk_msg.rpc_resp);
 	}
+	rpc_sleep_on(&req->rq_xprt->pending, task, NULL);
+	skb_frag_destructor_unref(&req->destructor);
 	dprintk("RPC: %5u call_decode result %d\n", task->tk_pid,
 			task->tk_status);
 	return;
@@ -1926,6 +1932,17 @@ out_retry:
 	}
 }
 
+/*
+ * 8.	Wait for pages to be released by the network stack.
+ */
+static void
+call_complete(struct rpc_task *task)
+{
+	dprintk("RPC: %5u call_complete result %d\n",
+		task->tk_pid, task->tk_status);
+	task->tk_action = rpc_exit_task;
+}
+
 static __be32 *
 rpc_encode_header(struct rpc_task *task)
 {
diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index f6d8c73..1145929 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -198,7 +198,8 @@ int svc_send_common(struct socket *sock, struct xdr_buf *xdr,
 	while (pglen > 0) {
 		if (slen == size)
 			flags = 0;
-		result = kernel_sendpage(sock, *ppage, NULL, base, size, flags);
+		result = kernel_sendpage(sock, *ppage, xdr->destructor,
+					 base, size, flags);
 		if (result > 0)
 			len += result;
 		if (result != size)
diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 6fe2dce..f8418a0 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1108,6 +1108,16 @@ static inline void xprt_init_xid(struct rpc_xprt *xprt)
 	xprt->xid = net_random();
 }
 
+static int xprt_complete_skb_pages(struct skb_frag_destructor *destroy)
+{
+	struct rpc_rqst	*req =
+		container_of(destroy, struct rpc_rqst, destructor);
+
+	dprintk("RPC: %5u completing skb pages\n", req->rq_task->tk_pid);
+	rpc_wake_up_queued_task(&req->rq_xprt->pending, req->rq_task);
+	return 0;
+}
+
 static void xprt_request_init(struct rpc_task *task, struct rpc_xprt *xprt)
 {
 	struct rpc_rqst	*req = task->tk_rqstp;
@@ -1120,6 +1130,8 @@ static void xprt_request_init(struct rpc_task *task, struct rpc_xprt *xprt)
 	req->rq_xid     = xprt_alloc_xid(xprt);
 	req->rq_release_snd_buf = NULL;
 	xprt_reset_majortimeo(req);
+	atomic_set(&req->destructor.ref, 1);
+	req->destructor.destroy = &xprt_complete_skb_pages;
 	dprintk("RPC: %5u reserved req %p xid %08x\n", task->tk_pid,
 			req, ntohl(req->rq_xid));
 }
diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index f1995dc..44e07f3 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -408,7 +408,8 @@ static int xs_send_pagedata(struct socket *sock, struct xdr_buf *xdr, unsigned i
 		remainder -= len;
 		if (remainder != 0 || more)
 			flags |= MSG_MORE;
-		err = sock->ops->sendpage(sock, *ppage, NULL, base, len, flags);
+		err = sock->ops->sendpage(sock, *ppage, xdr->destructor,
+					  base, len, flags);
 		if (remainder == 0 || err != len)
 			break;
 		sent += err;
-- 
1.7.2.5