Re: [PATCH v3 05/15] SUNRPC: Add helpers to prevent socket create from racing

[Olga Kornievskaia <aglo@umich.edu>]

Oops. config error. please ignore that.

On Thu, Sep 29, 2016 at 2:52 PM, Olga Kornievskaia <aglo@umich.edu> wrote:
> Hi Trond,
>
> Have you tried nfsv3 mount with this patch?
>
> Currently with this patch upstream kernel hangs.
>
> On Mon, Feb 9, 2015 at 5:48 PM, Trond Myklebust
> <trond.myklebust@primarydata.com> wrote:
>> The socket lock is currently held by the task that is requesting the
>> connection be established. While that is efficient in the case where
>> the connection happens quickly, it is racy in the case where it doesn't.
>> What we really want is for the connect helper to be able to block access
>> to the socket while it is being set up.
>>
>> This patch does so by arranging to transfer the socket lock from the
>> task that is requesting the connect attempt, and then releasing that
>> lock once everything is done.
>> This scheme also gives us automatic protection against collisions with
>> the RPC close code, so we can kill the cancel_delayed_work_sync()
>> call in xs_close().
>>
>> Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
>> ---
>>  include/linux/sunrpc/xprt.h |  3 +++
>>  net/sunrpc/xprt.c           | 37 +++++++++++++++++++++++++++++++++----
>>  net/sunrpc/xprtsock.c       |  7 +++++--
>>  3 files changed, 41 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
>> index 9d27ac45b909..2926e618dbc6 100644
>> --- a/include/linux/sunrpc/xprt.h
>> +++ b/include/linux/sunrpc/xprt.h
>> @@ -347,6 +347,9 @@ void                        xprt_force_disconnect(struct rpc_xprt *xprt);
>>  void                   xprt_conditional_disconnect(struct rpc_xprt *xprt, unsigned int cookie);
>>  int                    xs_swapper(struct rpc_xprt *xprt, int enable);
>>
>> +bool                   xprt_lock_connect(struct rpc_xprt *, struct rpc_task *, void *);
>> +void                   xprt_unlock_connect(struct rpc_xprt *, void *);
>> +
>>  /*
>>   * Reserved bit positions in xprt->state
>>   */
>> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
>> index ebbefad21a37..ff3574df8344 100644
>> --- a/net/sunrpc/xprt.c
>> +++ b/net/sunrpc/xprt.c
>> @@ -690,6 +690,37 @@ out_abort:
>>         spin_unlock(&xprt->transport_lock);
>>  }
>>
>> +bool xprt_lock_connect(struct rpc_xprt *xprt,
>> +               struct rpc_task *task,
>> +               void *cookie)
>> +{
>> +       bool ret = false;
>> +
>> +       spin_lock_bh(&xprt->transport_lock);
>> +       if (!test_bit(XPRT_LOCKED, &xprt->state))
>> +               goto out;
>> +       if (xprt->snd_task != task)
>> +               goto out;
>> +       xprt->snd_task = cookie;
>> +       ret = true;
>> +out:
>> +       spin_unlock_bh(&xprt->transport_lock);
>> +       return ret;
>> +}
>> +
>> +void xprt_unlock_connect(struct rpc_xprt *xprt, void *cookie)
>> +{
>> +       spin_lock_bh(&xprt->transport_lock);
>> +       if (xprt->snd_task != cookie)
>> +               goto out;
>> +       if (!test_bit(XPRT_LOCKED, &xprt->state))
>> +               goto out;
>> +       xprt->snd_task =NULL;
>> +       xprt->ops->release_xprt(xprt, NULL);
>> +out:
>> +       spin_unlock_bh(&xprt->transport_lock);
>> +}
>> +
>>  /**
>>   * xprt_connect - schedule a transport connect operation
>>   * @task: RPC task that is requesting the connect
>> @@ -712,9 +743,7 @@ void xprt_connect(struct rpc_task *task)
>>         if (test_and_clear_bit(XPRT_CLOSE_WAIT, &xprt->state))
>>                 xprt->ops->close(xprt);
>>
>> -       if (xprt_connected(xprt))
>> -               xprt_release_write(xprt, task);
>> -       else {
>> +       if (!xprt_connected(xprt)) {
>>                 task->tk_rqstp->rq_bytes_sent = 0;
>>                 task->tk_timeout = task->tk_rqstp->rq_timeout;
>>                 rpc_sleep_on(&xprt->pending, task, xprt_connect_status);
>> @@ -726,6 +755,7 @@ void xprt_connect(struct rpc_task *task)
>>                 xprt->stat.connect_start = jiffies;
>>                 xprt->ops->connect(xprt, task);
>>         }
>> +       xprt_release_write(xprt, task);
>>  }
>>
>>  static void xprt_connect_status(struct rpc_task *task)
>> @@ -758,7 +788,6 @@ static void xprt_connect_status(struct rpc_task *task)
>>                 dprintk("RPC: %5u xprt_connect_status: error %d connecting to "
>>                                 "server %s\n", task->tk_pid, -task->tk_status,
>>                                 xprt->servername);
>> -               xprt_release_write(xprt, task);
>>                 task->tk_status = -EIO;
>>         }
>>  }
>> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
>> index 0fa7ed93dc20..e57d8ed2c4d8 100644
>> --- a/net/sunrpc/xprtsock.c
>> +++ b/net/sunrpc/xprtsock.c
>> @@ -852,8 +852,6 @@ static void xs_close(struct rpc_xprt *xprt)
>>
>>         dprintk("RPC:       xs_close xprt %p\n", xprt);
>>
>> -       cancel_delayed_work_sync(&transport->connect_worker);
>> -
>>         xs_reset_transport(transport);
>>         xprt->reestablish_timeout = 0;
>>
>> @@ -2101,6 +2099,7 @@ static void xs_udp_setup_socket(struct work_struct *work)
>>         trace_rpc_socket_connect(xprt, sock, 0);
>>         status = 0;
>>  out:
>> +       xprt_unlock_connect(xprt, transport);
>>         xprt_clear_connecting(xprt);
>>         xprt_wake_pending_tasks(xprt, status);
>>  }
>> @@ -2286,6 +2285,7 @@ static void xs_tcp_setup_socket(struct work_struct *work)
>>         case 0:
>>         case -EINPROGRESS:
>>         case -EALREADY:
>> +               xprt_unlock_connect(xprt, transport);
>>                 xprt_clear_connecting(xprt);
>>                 return;
>>         case -EINVAL:
>> @@ -2303,6 +2303,7 @@ static void xs_tcp_setup_socket(struct work_struct *work)
>>  out_eagain:
>>         status = -EAGAIN;
>>  out:
>> +       xprt_unlock_connect(xprt, transport);
>>         xprt_clear_connecting(xprt);
>>         xprt_wake_pending_tasks(xprt, status);
>>  }
>> @@ -2325,6 +2326,8 @@ static void xs_connect(struct rpc_xprt *xprt, struct rpc_task *task)
>>  {
>>         struct sock_xprt *transport = container_of(xprt, struct sock_xprt, xprt);
>>
>> +       WARN_ON_ONCE(!xprt_lock_connect(xprt, task, transport));
>> +
>>         if (transport->sock != NULL && !RPC_IS_SOFTCONN(task)) {
>>                 dprintk("RPC:       xs_connect delayed xprt %p for %lu "
>>                                 "seconds\n",
>> --
>> 2.1.0
>>
>> --
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