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

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Date:	Tue, 22 May 2012 19:03:37 +0400
From:	Stanislav Kinsbursky <skinsbursky@...allels.com>
To:	"Myklebust, Trond" <Trond.Myklebust@...app.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 22.05.2012 18:29, Myklebust, Trond 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.
>

It looks like in this case we will have another races:

CPU#0						CPU#1
_____						_____

nfs4_init_client
nfs_idmap_new
nfs_idmap_register
rpc_get_sb_net (fail - no pipefs)
  					rpc_fill_super
  					rpc_pipefs_event
  					nfs_get_client_for_event
					(skip client - NFS_CS_READY is not set)
nfs_mark_client_ready(NFS_CS_READY)


And we are having client without idmap pipe...


> Cheers
>    Trond
>


-- 
Best regards,
Stanislav Kinsbursky
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