linux-kernel - Re: [PATCH v2] SUNRPC: check current nsproxy before set of node name on client creation

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Date:	Mon, 10 Sep 2012 12:43:31 +0400
From:	Stanislav Kinsbursky <skinsbursky@...allels.com>
To:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
CC:	Jeff Layton <jlayton@...hat.com>,
	"bfields@...ldses.org" <bfields@...ldses.org>,
	"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: check current nsproxy before set of node name
 on client creation

08.09.2012 18:33, Myklebust, Trond пишет:
> On Sat, 2012-09-08 at 08:59 +0300, Stanislav Kinsbursky wrote:
>> 08.09.2012 01:32, Myklebust, Trond пишет:
>>> On Mon, 2012-08-13 at 08:10 -0400, Jeff Layton wrote:
>>>> On Mon, 13 Aug 2012 15:37:31 +0400
>>>> Stanislav Kinsbursky <skinsbursky@...allels.com> wrote:
>>>>
>>>>> v2:
>>>>> 1) rpc_clnt_set_nodename() prototype updated.
>>>>> 2) fixed errors in comment.
>>>>>
>>>>> When child reaper exits, it can destroy mount namespace it belongs to, and if
>>>>> there are NFS mounts inside, then it will try to umount them. But in this
>>>>> point current->nsproxy is set to NULL and all namespaces will be destroyed one
>>>>> by one. I.e. we can't dereference current->nsproxy to obtain uts namespace.
>>>>>
>>>>> Signed-off-by: Stanislav Kinsbursky <skinsbursky@...allels.com>
>>>>> ---
>>>>>    net/sunrpc/clnt.c |   16 +++++++++++++---
>>>>>    1 files changed, 13 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
>>>>> index 9a9676e..8fbcbc8 100644
>>>>> --- a/net/sunrpc/clnt.c
>>>>> +++ b/net/sunrpc/clnt.c
>>>>> @@ -277,8 +277,18 @@ void rpc_clients_notifier_unregister(void)
>>>>>    	return rpc_pipefs_notifier_unregister(&rpc_clients_block);
>>>>>    }
>>>>>
>>>>> -static void rpc_clnt_set_nodename(struct rpc_clnt *clnt, const char *nodename)
>>>>> +static void rpc_clnt_set_nodename(struct rpc_clnt *clnt)
>>>>>    {
>>>>> +	const char *nodename;
>>>>> +
>>>>> +	/*
>>>>> +	 * We have to protect against dying child reaper, which has released
>>>>> +	 * its nsproxy already and is trying to destroy mount namespace.
>>>>> +	 */
>>>>> +	if (current->nsproxy == NULL)
>>>>> +		return;
>>>>> +
>>>>> +	nodename = utsname()->nodename;
>>>>>    	clnt->cl_nodelen = strlen(nodename);
>>>>>    	if (clnt->cl_nodelen > UNX_MAXNODENAME)
>>>>>    		clnt->cl_nodelen = UNX_MAXNODENAME;
>>>>> @@ -365,7 +375,7 @@ static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, stru
>>>>>    	}
>>>>>
>>>>>    	/* save the nodename */
>>>>> -	rpc_clnt_set_nodename(clnt, utsname()->nodename);
>>>>> +	rpc_clnt_set_nodename(clnt);
>>>>>    	rpc_register_client(clnt);
>>>>>    	return clnt;
>>>>>
>>>>> @@ -524,7 +534,7 @@ rpc_clone_client(struct rpc_clnt *clnt)
>>>>>    	err = rpc_setup_pipedir(new, clnt->cl_program->pipe_dir_name);
>>>>>    	if (err != 0)
>>>>>    		goto out_no_path;
>>>>> -	rpc_clnt_set_nodename(new, utsname()->nodename);
>>>>> +	rpc_clnt_set_nodename(new);
>>>>>    	if (new->cl_auth)
>>>>>    		atomic_inc(&new->cl_auth->au_count);
>>>>>    	atomic_inc(&clnt->cl_count);
>>>>>
>>>>> --
>>>>> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
>>>>> the body of a message to majordomo@...r.kernel.org
>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>> Acked-by: Jeff Layton <jlayton@...hat.com>
>>> OK, colour me confused (again).
>>
>> What color?
>>
>>> Why should a umount trigger an
>>> rpc_create() or rpc_clone_client()?
>>
>> It calls nsm_create().
>> Here is the trace (https://bugzilla.redhat.com/show_bug.cgi?id=830862,
>> comment 68):
>
> Right, but if we're using NFSv3 lock monitoring, we know in advance that
> we're going to need an nsm call to localhost. Why can't we just cache
> the one that we used to start lock monitoring in the first place?
>

Do you suggest to cache the call or the client for the call?

-- 
Best regards,
Stanislav Kinsbursky
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