linux-kernel - Re: [PATCH v2] SUNRPC: skip dead but not buried clients on PipeFS events

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Message-ID: <1335380095.15862.26.camel@lade.trondhjem.org>
Date:	Wed, 25 Apr 2012 18:54:55 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
CC:	Stanislav Kinsbursky <skinsbursky@...allels.com>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...nvz.org" <devel@...nvz.org>
Subject: Re: [PATCH v2] SUNRPC: skip dead but not buried clients on PipeFS
 events

On Wed, 2012-04-25 at 13:30 -0400, J. Bruce Fields wrote:
> On Fri, Apr 20, 2012 at 06:11:02PM +0400, Stanislav Kinsbursky wrote:
> > v2: atomic_inc_return() was replaced by atomic_inc_not_zero().
> > 
> > These clients can't be safely dereferenced if their counter in 0.
> 
> I'm pretty confused by how these notifiers work....
> 
> rpc_release_client decrements cl_count to zero temporarily, to have it
> immediately re-incremented by rpc_free_auth.
> 
> So if we're called concurrently with rpc_release_client then it's sort
> of random whether someone gets this callback.
> 
> Is that a problem?

Not really. If we re-increment the client->cl_count in rpc_free_auth()
then it would be so that we can send off a bunch of NULL rpc calls to
destroy existing RPCSEC_GSS contexts. We shouldn't need to do any more
upcalls in pipefs.

If we care, we could simply move the call to rpc_unregister_client()
into rpc_free_auth() so that the pipefs notifier doesn't see us, or we
could set a flag to have it ignore us.

> Also, is this an existing bug?  (In which case Trond should take it
> now.)


-- 
Trond Myklebust
Linux NFS client maintainer

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