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

NeilBrown
2011-11-08T00:13:56Z

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On Mon, 07 Nov 2011 14:49:03 -0500 Trond Myklebust
<Trond.Myklebust@netapp.com> wrote:

> On Sun, 2011-11-06 at 20:06 -0800, 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.
> >
> > 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?
> >
> > 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);
> > + }
>
> This is basically rpc_wake_up_status() with an extra conditional test
> (which again is just rpc_wake_up() with an extra status argument).
> Should we consider merging these functions?

I wondered a bit about this, but felt it safest to leave the code structured
as it was.
You could possibly combine them all into one function with:

if ((task->tk_flags & flags) == flags) {
if (status < 0)
task->tk_status = status;
rpc_wake_up.....
}
in the heart of the loop. Though that would only be right if
rpc_wake_up_status was never called with a zero status (or positive).

>
> > + if (head == &queue->tasks[0])
> > + break;
> > + head--;
> > + }
> > + spin_unlock_bh(&queue->lock);
> > +}
> > +EXPORT_SYMBOL_GPL(rpc_wake_up_softconn_status);
>
> Why do we want to export this?
>

We probably don't. It is just a copy/paste artefact.

If you agree with the approach, and suggest how you would like to handle the
proliferation of rpc_wake_up_* I can respin that patch as a formal submission.

Thanks,
NeilBrown

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