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

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Message-ID: <4FBBB0DB.6050708@parallels.com>
Date:	Tue, 22 May 2012 19:29:31 +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 19:00, Myklebust, Trond wrote:
> 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?
>

Sorry, but I don't understand the idea...
Where are you proposing to call this function?
In __rpc_pipefs_event() prior to dentries creatios?


-- 
Best regards,
Stanislav Kinsbursky
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