SUNRPC: Fixup socket wait for memory

We're seeing hangs in the NFS client code, with loops of the form:

 RPC: 30317 xmit incomplete (267368 left of 524448)
 RPC: 30317 call_status (status -11)
 RPC: 30317 call_transmit (status 0)
 RPC: 30317 xprt_prepare_transmit
 RPC: 30317 xprt_transmit(524448)
 RPC:       xs_tcp_send_request(267368) = -11
 RPC: 30317 xmit incomplete (267368 left of 524448)
 RPC: 30317 call_status (status -11)
 RPC: 30317 call_transmit (status 0)
 RPC: 30317 xprt_prepare_transmit
 RPC: 30317 xprt_transmit(524448)

Turns out commit ceb5d58b2170 ("net: fix sock_wake_async() rcu protection")
moved SOCKWQ_ASYNC_NOSPACE out of sock->flags and into sk->sk_wq->flags,
however it never tried to fix up the code in net/sunrpc.

The new idiom is to use the flags in the RCU protected struct socket_wq.
While we're at it, clear out the now redundant places where we set/clear
SOCKWQ_ASYNC_NOSPACE and SOCK_NOSPACE. In principle, sk_stream_wait_memory()
is supposed to set these for us, so we only need to clear them in the
particular case of our ->write_space() callback.

Fixes: ceb5d58b2170 ("net: fix sock_wake_async() rcu protection")
Cc: Eric Dumazet <edumazet@google.com>
Cc: stable@vger.kernel.org # 4.4
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 21 insertions, 28 deletions

diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 2ffaf6a79499..027c9ef8a263 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -398,7 +398,6 @@ static int xs_sendpages(struct socket *sock, struct sockaddr *addr, int addrlen,
         if (unlikely(!sock))
                 return -ENOTSOCK;
 
-        clear_bit(SOCKWQ_ASYNC_NOSPACE, &sock->flags);
         if (base != 0) {
                 addr = NULL;
                 addrlen = 0;
@@ -442,7 +441,6 @@ static void xs_nospace_callback(struct rpc_task *task)
         struct sock_xprt *transport = container_of(task->tk_rqstp->rq_xprt, struct sock_xprt, xprt);
 
         transport->inet->sk_write_pending--;
-        clear_bit(SOCKWQ_ASYNC_NOSPACE, &transport->sock->flags);
 }
 
 /**
@@ -467,20 +465,11 @@ static int xs_nospace(struct rpc_task *task)
 
         /* Don't race with disconnect */
         if (xprt_connected(xprt)) {
-                if (test_bit(SOCKWQ_ASYNC_NOSPACE, &transport->sock->flags)) {
-                        /*
-                         * Notify TCP that we're limited by the application
-                         * window size
-                         */
-                        set_bit(SOCK_NOSPACE, &transport->sock->flags);
-                        sk->sk_write_pending++;
-                        /* ...and wait for more buffer space */
-                        xprt_wait_for_buffer_space(task, xs_nospace_callback);
-                }
-        } else {
-                clear_bit(SOCKWQ_ASYNC_NOSPACE, &transport->sock->flags);
+                /* wait for more buffer space */
+                sk->sk_write_pending++;
+                xprt_wait_for_buffer_space(task, xs_nospace_callback);
+        } else
                 ret = -ENOTCONN;
-        }
 
         spin_unlock_bh(&xprt->transport_lock);
 
@@ -616,9 +605,6 @@ process_status:
         case -EAGAIN:
                 status = xs_nospace(task);
                 break;
-        default:
-                dprintk("RPC:       sendmsg returned unrecognized error %d\n",
-                        -status);
         case -ENETUNREACH:
         case -ENOBUFS:
         case -EPIPE:
@@ -626,7 +612,10 @@ process_status:
         case -EPERM:
                 /* When the server has died, an ICMP port unreachable message
                  * prompts ECONNREFUSED. */
-                clear_bit(SOCKWQ_ASYNC_NOSPACE, &transport->sock->flags);
+                break;
+        default:
+                dprintk("RPC:       sendmsg returned unrecognized error %d\n",
+                        -status);
         }
 
         return status;
@@ -706,16 +695,16 @@ static int xs_tcp_send_request(struct rpc_task *task)
         case -EAGAIN:
                 status = xs_nospace(task);
                 break;
-        default:
-                dprintk("RPC:       sendmsg returned unrecognized error %d\n",
-                        -status);
         case -ECONNRESET:
         case -ECONNREFUSED:
         case -ENOTCONN:
         case -EADDRINUSE:
         case -ENOBUFS:
         case -EPIPE:
-                clear_bit(SOCKWQ_ASYNC_NOSPACE, &transport->sock->flags);
+                break;
+        default:
+                dprintk("RPC:       sendmsg returned unrecognized error %d\n",
+                        -status);
         }
 
         return status;
@@ -1609,19 +1598,23 @@ static void xs_tcp_state_change(struct sock *sk)
 
 static void xs_write_space(struct sock *sk)
 {
-        struct socket *sock;
+        struct socket_wq *wq;
         struct rpc_xprt *xprt;
 
-        if (unlikely(!(sock = sk->sk_socket)))
+        if (!sk->sk_socket)
                 return;
-        clear_bit(SOCK_NOSPACE, &sock->flags);
+        clear_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
 
         if (unlikely(!(xprt = xprt_from_sock(sk))))
                 return;
-        if (test_and_clear_bit(SOCKWQ_ASYNC_NOSPACE, &sock->flags) == 0)
-                return;
+        rcu_read_lock();
+        wq = rcu_dereference(sk->sk_wq);
+        if (!wq || test_and_clear_bit(SOCKWQ_ASYNC_NOSPACE, &wq->flags) == 0)
+                goto out;
 
         xprt_write_space(xprt);
+out:
+        rcu_read_unlock();
 }
 
 /**