[PATCH 3.10 52/97] SUNRPC: Fix races in xs_nospace()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

3.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Trond Myklebust <trond.myklebust@primarydata.com>

commit 06ea0bfe6e6043cb56a78935a19f6f8ebc636226 upstream.

When a send failure occurs due to the socket being out of buffer space,
we call xs_nospace() in order to have the RPC task wait until the
socket has drained enough to make it worth while trying again.
The current patch fixes a race in which the socket is drained before
we get round to setting up the machinery in xs_nospace(), and which
is reported to cause hangs.

Link: http://lkml.kernel.org/r/20140210170315.33dfc621@notabene.brown
Fixes: a9a6b52ee1ba (SUNRPC: Don't start the retransmission timer...)
Reported-by: Neil Brown <neilb@suse.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/sunrpc/xprtsock.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -502,6 +502,7 @@ static int xs_nospace(struct rpc_task *t
 	struct rpc_rqst *req = task->tk_rqstp;
 	struct rpc_xprt *xprt = req->rq_xprt;
 	struct sock_xprt *transport = container_of(xprt, struct sock_xprt, xprt);
+	struct sock *sk = transport->inet;
 	int ret = -EAGAIN;
 
 	dprintk("RPC: %5u xmit incomplete (%u left of %u)\n",
@@ -519,7 +520,7 @@ static int xs_nospace(struct rpc_task *t
 			 * window size
 			 */
 			set_bit(SOCK_NOSPACE, &transport->sock->flags);
-			transport->inet->sk_write_pending++;
+			sk->sk_write_pending++;
 			/* ...and wait for more buffer space */
 			xprt_wait_for_buffer_space(task, xs_nospace_callback);
 		}
@@ -529,6 +530,9 @@ static int xs_nospace(struct rpc_task *t
 	}
 
 	spin_unlock_bh(&xprt->transport_lock);
+
+	/* Race breaker in case memory is freed before above code is called */
+	sk->sk_write_space(sk);
 	return ret;
 }