Re: [PATCH v5 1/8] SUNRPC: introduce helpers for reference countedrpcbind clients

[Stanislav Kinsbursky]

20.09.2011 18:24, Jeff Layton ÐÐÑÐÑ:
> On Tue, 20 Sep 2011 17:49:27 +0400
> Stanislav Kinsbursky<skinsbursky@xxxxxxxxxxxxx>  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@xxxxxxxxxxxxx>
> >
> > ---
> >    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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