Re: [PATCH] sunrpc: wake up SOFTCONN tasks when a connection error happens.

Chuck Lever
2011-11-07T14:57:20Z

On Nov 6, 2011, at 11:06 PM, NeilBrown wrote:

>
> hi all,
> It being over a year since I last raised this I thought it might be time to
> try again.
>
> The problem is that an NFSv4 mount request (the default) to an unrouteable
> server results in a 3 minute timeout instead of an instant failure.
>
> This is easy to test by simply removing your default route then trying to
> mount something outside your local network.

Awesome, thanks for the simple reproducer!

> This patch causes any SOFTCONN task to be woken up as soon as a connection
> error occurs so that it can fail promptly. The failure reasons gets passed
> back and as it is not ETIMEDOUT it causes immediate failure.
>
> Is this a reasonable approach?

I don't have a philosophical objection to this. However, Trond knows the architecture of TCP reconnection the best; I can't comment on the choice of returning the actual errno instead of ETIMEDOUT.

> Thanks,
> NeilBrown
>
>
>
>
> From a1aea8fc3977ffa9951c3d7f27dbb1905e5f560f Mon Sep 17 00:00:00 2001
> From: NeilBrown <neilb@suse.de>
> Date: Mon, 7 Nov 2011 15:00:17 +1100
> Subject: [PATCH] sunrpc: wake up SOFTCONN tasks when a connection error
> happens.
>
> A 'SOFTCONN' task should fail if there is an error or a major timeout
> during connection.
>
> However errors are currently converted into a timeout (60seconds for
> TCP) which is treated as a minor timeout and 3 of these are required
> before failure.
>
> The result of this is that if you try to mount an NFSv4 filesystem
> (which doesn't require rpcbind and the failure modes that provides)
> from a server which you do not have a route to (an so get
> NETUNREACHABLE), you have an unnecessary 3 minutes timeout.
>
> So when ENETUNREACH is reported for a connection - or other errors
> which are fatal, wake up any SOFTCONN tasks with that error - rather
> than letting them wait 60 seconds and then generate ETIMEDOUT.
>
> This causes the above mentioned mount attempt to fail instantly.
>
> Signed-off-by: NeilBrown <neilb@suse.de>
> ---
> include/linux/sunrpc/sched.h | 1 +
> net/sunrpc/sched.c | 29 +++++++++++++++++++++++++++++
> net/sunrpc/xprtsock.c | 6 +++++-
> 3 files changed, 35 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/sunrpc/sched.h b/include/linux/sunrpc/sched.h
> index e775689..b85451b 100644
> --- a/include/linux/sunrpc/sched.h
> +++ b/include/linux/sunrpc/sched.h
> @@ -236,6 +236,7 @@ void rpc_wake_up_queued_task(struct rpc_wait_queue *,
> void rpc_wake_up(struct rpc_wait_queue *);
> struct rpc_task *rpc_wake_up_next(struct rpc_wait_queue *);
> void rpc_wake_up_status(struct rpc_wait_queue *, int);
> +void rpc_wake_up_softconn_status(struct rpc_wait_queue *, int);
> int rpc_queue_empty(struct rpc_wait_queue *);
> void rpc_delay(struct rpc_task *, unsigned long);
> void * rpc_malloc(struct rpc_task *, size_t);
> diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
> index d12ffa5..d92000a 100644
> --- a/net/sunrpc/sched.c
> +++ b/net/sunrpc/sched.c
> @@ -543,6 +543,35 @@ void rpc_wake_up_status(struct rpc_wait_queue *queue, int status)
> }
> EXPORT_SYMBOL_GPL(rpc_wake_up_status);
>
> +/**
> + * rpc_wake_up_softconn_status - wake up all SOFTCONN rpc_tasks and set their
> + * status value.
> + * @queue: rpc_wait_queue on which the tasks are sleeping
> + * @status: status value to set
> + *
> + * Grabs queue->lock
> + */
> +void rpc_wake_up_softconn_status(struct rpc_wait_queue *queue, int status)
> +{
> + struct rpc_task *task, *next;
> + struct list_head *head;
> +
> + spin_lock_bh(&queue->lock);
> + head = &queue->tasks[queue->maxpriority];
> + for (;;) {
> + list_for_each_entry_safe(task, next, head, u.tk_wait.list)
> + if (RPC_IS_SOFTCONN(task)) {
> + task->tk_status = status;
> + rpc_wake_up_task_queue_locked(queue, task);
> + }
> + if (head == &queue->tasks[0])
> + break;
> + head--;
> + }
> + spin_unlock_bh(&queue->lock);
> +}
> +EXPORT_SYMBOL_GPL(rpc_wake_up_softconn_status);
> +
> static void __rpc_queue_timer_fn(unsigned long ptr)
> {
> struct rpc_wait_queue *queue = (struct rpc_wait_queue *)ptr;
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index d7f97ef..02c683b 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -2158,7 +2158,11 @@ static void xs_tcp_setup_socket(struct work_struct *work)
> case -ECONNREFUSED:
> case -ECONNRESET:
> case -ENETUNREACH:
> - /* retry with existing socket, after a delay */
> + /* Retry with existing socket after a delay, except
> + * for SOFTCONN tasks which fail. */
> + xprt_clear_connecting(xprt);
> + rpc_wake_up_softconn_status(&xprt->pending, status);
> + return;
> case 0:
> case -EINPROGRESS:
> case -EALREADY:
> --
> 1.7.7
>

--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com