SUNRPC: Fix races in xs_nospace()

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>
Cc: stable@vger.kernel.org
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 817a1e5..0addefc 100644 (file)
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -510,6 +510,7 @@ static int xs_nospace(struct rpc_task *task)
        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",
@@ -527,7 +528,7 @@ static int xs_nospace(struct rpc_task *task)
                         * 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);
                }
@@ -537,6 +538,9 @@ static int xs_nospace(struct rpc_task *task)
        }
 
        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;
 }