netdev - Re: [PATCH 5/5] sunrpc/auth_gss: Call rcu

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Date:	Mon, 08 Jun 2009 13:00:49 -0400
From:	Trond Myklebust <Trond.Myklebust@...app.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Jesper Dangaard Brouer <hawk@...x.dk>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, urs.thuermann@...kswagen.de,
	oliver.hartkopp@...kswagen.de, wg@...ndegger.com,
	vladislav.yasevich@...com, sri@...ibm.com,
	linux-sctp@...r.kernel.org, linux-nfs@...r.kernel.org,
	netfilter-devel@...r.kernel.org
Subject: Re: [PATCH 5/5] sunrpc/auth_gss: Call rcu_barrier() on module
 unload.

On Mon, 2009-06-08 at 09:26 -0700, Paul E. McKenney wrote:
> On Mon, Jun 08, 2009 at 03:11:48PM +0200, Jesper Dangaard Brouer wrote:
> > As the module uses rcu_call() we should make sure that all
> > rcu callback has been completed before removing the code.
> 
> Good improvement!!!  Assuming that gss_svc_shutdown() and
> rpcauth_unregister() prevent any future RCU callbacks to be registered,
> this patch will fix things up.
> 
> Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> > Signed-off-by: Jesper Dangaard Brouer <hawk@...x.dk>
> > ---
> > 
> >  net/sunrpc/auth_gss/auth_gss.c |    1 +
> >  1 files changed, 1 insertions(+), 0 deletions(-)
> > 
> > diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
> > index e630b38..66d458f 100644
> > --- a/net/sunrpc/auth_gss/auth_gss.c
> > +++ b/net/sunrpc/auth_gss/auth_gss.c
> > @@ -1548,6 +1548,7 @@ static void __exit exit_rpcsec_gss(void)
> >  {
> >  	gss_svc_shutdown();
> >  	rpcauth_unregister(&authgss_ops);
> > +	rcu_barrier(); /* Wait for completion of call_rcu()'s */
> >  }
> > 
> >  MODULE_LICENSE("GPL");
> > 

Hmm... If this is about ensuring that all the call_rcu() callbacks
complete before we remove the module, then don't we also need similar
barriers in net/sunrpc/sunrpc_syms.c:cleanup_sunrpc() and in
fs/nfs/inode.c:exit_nfs_fs()?

Cheers
  Trond
-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com
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