[PATCH 10/10] sunrpc: use SKB fragment destructors to delay completion until page is released by network stack.

Ian Campbell
2012-04-10T14:26:24Z

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-Sxgqhf6Nn4DQT0dZR+AlfA@public.gmane.org>
Acked-by: Trond Myklebust <Trond.Myklebust-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org>
Cc: "David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>
Cc: Neil Brown <neilb-l3A5Bk7waGM@public.gmane.org>
Cc: "J. Bruce Fields" <bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org>
Cc: linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Cc: netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.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 7a4cb5f..4e94e2a 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -62,6 +62,7 @@ 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);
@@ -1417,6 +1418,8 @@ 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");
@@ -1582,6 +1585,7 @@ 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;
@@ -1615,8 +1619,8 @@ 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);
}

/*
@@ -1689,7 +1693,8 @@ 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);
@@ -1729,7 +1734,6 @@ 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 */

@@ -1907,12 +1911,14 @@ 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;
@@ -1927,6 +1933,17 @@ 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 706305b..efa95df 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 0cbcd1a..a252759 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 f05082b..b6ee8b7 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

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