linux-kernel - Re: [PATCH] NFS: init client before declaration

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Date:	Tue, 22 May 2012 15:00:17 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
CC:	"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] NFS: init client before declaration

On Tue, 2012-05-22 at 10:29 -0400, Trond Myklebust wrote:
> On Tue, 2012-05-22 at 16:40 +0400, Stanislav Kinsbursky wrote:
> > Client have to be initialized prior to adding it to per-net clients list,
> > because otherwise there are races, shown below:
> > 
> > CPU#0					CPU#1
> > _____					_____
> > 
> > nfs_get_client
> > nfs_alloc_client
> > list_add(..., nfs_client_list)
> > 					rpc_fill_super
> > 					rpc_pipefs_event
> > 					nfs_get_client_for_event
> > 					__rpc_pipefs_event
> > 					(clp->cl_rpcclient is uninitialized)
> > 					BUG()
> > init_client
> > clp->cl_rpcclient = ...
> > 
> 
> Why not simply change nfs_get_client_for_event() so that it doesn't
> touch nfs_clients that have clp->cl_cons_state!=NFS_CS_READY?
> 
> That should ensure that it doesn't touch nfs_clients that failed to
> initialise and/or are still in the process of being initialised.

...actually, come to think of it. Why not just add a helper function
"bool nfs_client_active(const struct nfs_client *clp)" to
fs/nfs/client.c that does a call to
	wait_event_killable(nfs_client_active_wq, clp->cl_cons_state < NFS_CS_INITING);
and checks the resulting value of clp->cl_cons_state?

-- 
Trond Myklebust
Linux NFS client maintainer

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