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Subject: Re: [PATCH 0/2] sunrpc: more reliable detection of running gssd
From: Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <1384261225-28559-1-git-send-email-jlayton@redhat.com>
Date: Tue, 12 Nov 2013 11:02:42 -0500
Cc: trond.myklebust@netapp.com, linux-nfs@vger.kernel.org, steved@redhat.com
Message-Id: <A0488E98-0DF9-4ECE-A39D-C8E460E4C546@oracle.com>
References: <1384261225-28559-1-git-send-email-jlayton@redhat.com>
To: Jeff Layton <jlayton@redhat.com>
Sender: linux-nfs-owner@vger.kernel.org


On Nov 12, 2013, at 8:00 AM, Jeff Layton <jlayton@redhat.com> wrote:

> We've gotten a lot of complaints recently about the 15s delay when
> doing a sec=sys mount without gssd running.
> 
> A large part of the problem is that the kernel isn't able to reliably
> detect when rpc.gssd is running. What we currently have is a
> gssd_running flag that is initially set to 1. When an upcall times out,
> that gets set to 0, and subsequent upcalls get a much shorter timeout
> (1/4s instead of 15s). It's reset back to '1' when a pipe is reopened.
> 
> The approach of using a flag like this is pretty inadequate. First, it
> doesn't eliminate the long delay on the initial upcall attempt. Also,
> if gssd spontaneously dies, then the flag will still be set to 1 until
> the next upcall attempt times out. Finally, it currently requires that
> the pipe be reopened in order to reset the flag back to true.
> 
> This patchset replaces that flag with a more reliable mechanism for
> detecting when gssd is running. When rpc_pipefs is mounted, it creates a
> new "dummy" pipe that gssd will naturally find and hold open. We'll
> never send an upcall down this pipe, and writing to it always fails.
> But, since we can detect when something is holding it open, we can use
> that to determine whether gssd is running.
> 
> The current patch just uses this mechanism to replace the gssd_running
> flag with this new mechanism. This shortens the long delay when mounting
> without gssd running, but does not silence these warnings:
> 
>    RPC: AUTH_GSS upcall timed out.
>    Please check user daemon is running.
> 
> I'm willing to add a patch to do that, but I'm a little unclear on the
> best way to do so. Those messages are generated by the auth_gss code. We
> probably do want to print them if someone mounted with sec=krb5, but
> suppress them when mounting with sec=sys.
> 
> Do we need to somehow pass down that intent to auth_gss? Another idea
> would be to call gssd_running() from the nfs mount code and use that to
> determine whether to try and use krb5 at all...
> 
> Discuss!

I'd like to pursue the module loading solution as well.


> 
> Jeff Layton (2):
>  sunrpc: create a new dummy pipe for gssd to hold open
>  sunrpc: replace sunrpc_net->gssd_running flag with a better mechanism
> 
> include/linux/sunrpc/rpc_pipe_fs.h |  4 ++
> net/sunrpc/auth_gss/auth_gss.c     | 13 ++++--
> net/sunrpc/netns.h                 |  3 +-
> net/sunrpc/rpc_pipe.c              | 95 ++++++++++++++++++++++++++++++++++++--
> 4 files changed, 106 insertions(+), 9 deletions(-)
> 
> -- 
> 1.8.3.1
> 
> --
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-- 
Chuck Lever
chuck[dot]lever[at]oracle[dot]com