linux-kernel - Re: [PATCH v5 1/8] SUNRPC: introduce helpers for reference counted rpcbind clients

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Date:	Tue, 20 Sep 2011 18:43:45 +0400
From:	Stanislav Kinsbursky <skinsbursky@...allels.com>
To:	Jeff Layton <jlayton@...hat.com>
CC:	"Trond.Myklebust@...app.com" <Trond.Myklebust@...app.com>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	Pavel Emelianov <xemul@...allels.com>,
	"neilb@...e.de" <neilb@...e.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"bfields@...ldses.org" <bfields@...ldses.org>,
	"davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [PATCH v5 1/8] SUNRPC: introduce helpers for reference counted
 rpcbind clients

20.09.2011 18:24, Jeff Layton пишет:
> On Tue, 20 Sep 2011 17:49:27 +0400
> Stanislav Kinsbursky<skinsbursky@...allels.com>  wrote:
>
>> v5: fixed races with rpcb_users in rpcb_get_local()
>>
>> This helpers will be used for dynamical creation and destruction of rpcbind
>> clients.
>> Variable rpcb_users is actually a counter of lauched RPC services. If rpcbind
>> clients has been created already, then we just increase rpcb_users.
>>
>> Signed-off-by: Stanislav Kinsbursky<skinsbursky@...allels.com>
>>
>> ---
>>    net/sunrpc/rpcb_clnt.c |   53 ++++++++++++++++++++++++++++++++++++++++++++++++
>>    1 files changed, 53 insertions(+), 0 deletions(-)
>>
>> diff --git a/net/sunrpc/rpcb_clnt.c b/net/sunrpc/rpcb_clnt.c
>> index e45d2fb..5f4a406 100644
>> --- a/net/sunrpc/rpcb_clnt.c
>> +++ b/net/sunrpc/rpcb_clnt.c
>> @@ -114,6 +114,9 @@ static struct rpc_program	rpcb_program;
>>    static struct rpc_clnt *	rpcb_local_clnt;
>>    static struct rpc_clnt *	rpcb_local_clnt4;
>>    +DEFINE_SPINLOCK(rpcb_clnt_lock);
>> +unsigned int			rpcb_users;
>> +
>>    struct rpcbind_args {
>>    	struct rpc_xprt *	r_xprt;
>>    @@ -161,6 +164,56 @@ static void rpcb_map_release(void *data)
>>    	kfree(map);
>>    }
>>    +static int rpcb_get_local(void)
>> +{
>> +	int cnt;
>> +
>> +	spin_lock(&rpcb_clnt_lock);
>> +	if (rpcb_users)
>> +		rpcb_users++;
>> +	cnt = rpcb_users;
>> +	spin_unlock(&rpcb_clnt_lock);
>> +
>> +	return cnt;
>> +}
>> +
>> +void rpcb_put_local(void)
>> +{
>> +	struct rpc_clnt *clnt = rpcb_local_clnt;
>> +	struct rpc_clnt *clnt4 = rpcb_local_clnt4;
>> +	int shutdown;
>> +
>> +	spin_lock(&rpcb_clnt_lock);
>> +	if (--rpcb_users == 0) {
>> +		rpcb_local_clnt = NULL;
>> +		rpcb_local_clnt4 = NULL;
>> +	}
>
> In the function below, you mention that the above pointers are
> protected by rpcb_create_local_mutex, but it looks like they get reset
> here without that being held?
>

Assigning of them is protected by rpcb_create_local_mutex.
Dereferencing of them is protected by rpcb_clnt_lock.

> Might it be simpler to just protect rpcb_users with the
> rpcb_create_local_mutex and ensure that it's held whenever you call one
> of these routines? None of these are codepaths are particularly hot.
>

I just inherited this lock-mutex logic.
Actually, you right. This codepaths are used rarely.
But are use sure, that we need to remove this "speed-up" logic if we take into 
account that it was here already?

>> +	shutdown = !rpcb_users;
>> +	spin_unlock(&rpcb_clnt_lock);
>> +
>> +	if (shutdown) {
>> +		/*
>> +		 * cleanup_rpcb_clnt - remove xprtsock's sysctls, unregister
>> +		 */
>> +		if (clnt4)
>> +			rpc_shutdown_client(clnt4);
>> +		if (clnt)
>> +			rpc_shutdown_client(clnt);
>> +	}
>> +	return;
>> +}
>> +
>> +static void rpcb_set_local(struct rpc_clnt *clnt, struct rpc_clnt *clnt4)
>> +{
>> +	/* Protected by rpcb_create_local_mutex */
>> +	rpcb_local_clnt = clnt;
>> +	rpcb_local_clnt4 = clnt4;
>> +	rpcb_users++;
>> +	dprintk("RPC:       created new rpcb local clients (rpcb_local_clnt: "
>> +			"%p, rpcb_local_clnt4: %p)\n", rpcb_local_clnt,
>> +			rpcb_local_clnt4);
>> +}
>> +
>>    /*
>>     * Returns zero on success, otherwise a negative errno value
>>     * is returned.
>> --
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>
>


-- 
Best regards,
Stanislav Kinsbursky
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