Re: [PATCH v2] lockd: get rid of reference-counted NSM RPC clients

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, Oct 07, 2015 at 02:39:55PM +0300, Andrey Ryabinin wrote:
> Currently we have reference-counted per-net NSM RPC client
> which created on the first monitor request and destroyed
> after the last unmonitor request. It's needed because
> RPC client need to know 'utsname()->nodename', but utsname()
> might be NULL when nsm_unmonitor() called.
> 
> So instead of holding the rpc client we could just save nodename
> in struct nlm_host and pass it to the rpc_create().
> Thus ther is no need in keeping rpc client until last
> unmonitor request. We could create separate RPC clients
> for each monitor/unmonitor requests.
> 
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> ---
>  Changes since v1:
>   - fixed build warning:
> 	 fs/lockd/mon.c:111:3: warning: format '%d' expects argument of type 'int', but argument 2 has type 'long int' [-Wformat=]
> 
>  fs/lockd/host.c             |  1 +
>  fs/lockd/mon.c              | 89 ++++++++-------------------------------------
>  fs/lockd/netns.h            |  3 --
>  fs/lockd/svc.c              |  1 -
>  include/linux/lockd/lockd.h |  1 +
>  5 files changed, 17 insertions(+), 78 deletions(-)

That's certainly a nice diffstat, thanks for the cleanup.  But
unfortunately this isn't code I look at very often.  One thing I'm
unsure about:

> 
> diff --git a/fs/lockd/host.c b/fs/lockd/host.c
> index b5f3c3a..d716c99 100644
> --- a/fs/lockd/host.c
> +++ b/fs/lockd/host.c
> @@ -161,6 +161,7 @@ static struct nlm_host *nlm_alloc_host(struct nlm_lookup_host_info *ni,
>  	host->h_nsmhandle  = nsm;
>  	host->h_addrbuf    = nsm->sm_addrbuf;
>  	host->net	   = ni->net;
> +	strlcpy(host->nodename, utsname()->nodename, sizeof(host->nodename));
>  
>  out:
>  	return host;
> diff --git a/fs/lockd/mon.c b/fs/lockd/mon.c
> index 6c05cd1..19166d4 100644
> --- a/fs/lockd/mon.c
> +++ b/fs/lockd/mon.c
> @@ -42,7 +42,7 @@ struct nsm_args {
>  	u32			proc;
>  
>  	char			*mon_name;
> -	char			*nodename;
> +	const char		*nodename;
>  };
>  
>  struct nsm_res {
> @@ -86,69 +86,18 @@ static struct rpc_clnt *nsm_create(struct net *net, const char *nodename)
>  	return rpc_create(&args);
>  }
>  
> -static struct rpc_clnt *nsm_client_set(struct lockd_net *ln,
> -		struct rpc_clnt *clnt)
> -{
> -	spin_lock(&ln->nsm_clnt_lock);
> -	if (ln->nsm_users == 0) {
> -		if (clnt == NULL)
> -			goto out;
> -		ln->nsm_clnt = clnt;
> -	}
> -	clnt = ln->nsm_clnt;
> -	ln->nsm_users++;
> -out:
> -	spin_unlock(&ln->nsm_clnt_lock);
> -	return clnt;
> -}
> -
> -static struct rpc_clnt *nsm_client_get(struct net *net, const char *nodename)
> -{
> -	struct rpc_clnt	*clnt, *new;
> -	struct lockd_net *ln = net_generic(net, lockd_net_id);
> -
> -	clnt = nsm_client_set(ln, NULL);
> -	if (clnt != NULL)
> -		goto out;
> -
> -	clnt = new = nsm_create(net, nodename);
> -	if (IS_ERR(clnt))
> -		goto out;
> -
> -	clnt = nsm_client_set(ln, new);
> -	if (clnt != new)
> -		rpc_shutdown_client(new);
> -out:
> -	return clnt;
> -}
> -
> -static void nsm_client_put(struct net *net)
> -{
> -	struct lockd_net *ln = net_generic(net, lockd_net_id);
> -	struct rpc_clnt	*clnt = NULL;
> -
> -	spin_lock(&ln->nsm_clnt_lock);
> -	ln->nsm_users--;
> -	if (ln->nsm_users == 0) {
> -		clnt = ln->nsm_clnt;
> -		ln->nsm_clnt = NULL;
> -	}
> -	spin_unlock(&ln->nsm_clnt_lock);
> -	if (clnt != NULL)
> -		rpc_shutdown_client(clnt);
> -}
> -
>  static int nsm_mon_unmon(struct nsm_handle *nsm, u32 proc, struct nsm_res *res,
> -			 struct rpc_clnt *clnt)
> +			 const struct nlm_host *host)
>  {
>  	int		status;
> +	struct rpc_clnt *clnt;
>  	struct nsm_args args = {
>  		.priv		= &nsm->sm_priv,
>  		.prog		= NLM_PROGRAM,
>  		.vers		= 3,
>  		.proc		= NLMPROC_NSM_NOTIFY,
>  		.mon_name	= nsm->sm_mon_name,
> -		.nodename	= clnt->cl_nodename,
> +		.nodename	= host->nodename,
>  	};
>  	struct rpc_message msg = {
>  		.rpc_argp	= &args,
> @@ -157,6 +106,13 @@ static int nsm_mon_unmon(struct nsm_handle *nsm, u32 proc, struct nsm_res *res,
>  
>  	memset(res, 0, sizeof(*res));
>  
> +	clnt = nsm_create(host->net, host->nodename);
> +	if (IS_ERR(clnt)) {
> +		dprintk("lockd: failed to create NSM upcall transport, "
> +			"status=%ld, net=%p\n", PTR_ERR(clnt), host->net);
> +		return PTR_ERR(clnt);
> +	}
> +
>  	msg.rpc_proc = &clnt->cl_procinfo[proc];
>  	status = rpc_call_sync(clnt, &msg, RPC_TASK_SOFTCONN);
>  	if (status == -ECONNREFUSED) {
> @@ -170,6 +126,8 @@ static int nsm_mon_unmon(struct nsm_handle *nsm, u32 proc, struct nsm_res *res,
>  				status);
>  	else
>  		status = 0;
> +
> +	rpc_shutdown_client(clnt);
>  	return status;
>  }
>  
> @@ -189,32 +147,19 @@ int nsm_monitor(const struct nlm_host *host)
>  	struct nsm_handle *nsm = host->h_nsmhandle;
>  	struct nsm_res	res;
>  	int		status;
> -	struct rpc_clnt *clnt;
> -	const char *nodename = NULL;
>  
>  	dprintk("lockd: nsm_monitor(%s)\n", nsm->sm_name);
>  
>  	if (nsm->sm_monitored)
>  		return 0;
>  
> -	if (host->h_rpcclnt)
> -		nodename = host->h_rpcclnt->cl_nodename;
> -
>  	/*
>  	 * Choose whether to record the caller_name or IP address of
>  	 * this peer in the local rpc.statd's database.
>  	 */
>  	nsm->sm_mon_name = nsm_use_hostnames ? nsm->sm_name : nsm->sm_addrbuf;
>  
> -	clnt = nsm_client_get(host->net, nodename);
> -	if (IS_ERR(clnt)) {
> -		status = PTR_ERR(clnt);
> -		dprintk("lockd: failed to create NSM upcall transport, "
> -				"status=%d, net=%p\n", status, host->net);
> -		return status;
> -	}
> -
> -	status = nsm_mon_unmon(nsm, NSMPROC_MON, &res, clnt);
> +	status = nsm_mon_unmon(nsm, NSMPROC_MON, &res, host);

OK, so here and in nsm_unmonitor we're unconditionally creating a new
rpc client every time, where previously we might have been reusing a
cached one?

In particular, I *think* the reference counting means that we never
actually had to create a new rpc client in the nsm_unmonitor case.  Are
we sure doing so doesn't cause any problems?

But I don't know this code well and haven't tried to review this
carefully, I may be worrying about nothing.

--b.

>  	if (unlikely(res.status != 0))
>  		status = -EIO;
>  	if (unlikely(status < 0)) {
> @@ -246,11 +191,9 @@ void nsm_unmonitor(const struct nlm_host *host)
>  
>  	if (atomic_read(&nsm->sm_count) == 1
>  	 && nsm->sm_monitored && !nsm->sm_sticky) {
> -		struct lockd_net *ln = net_generic(host->net, lockd_net_id);
> -
>  		dprintk("lockd: nsm_unmonitor(%s)\n", nsm->sm_name);
>  
> -		status = nsm_mon_unmon(nsm, NSMPROC_UNMON, &res, ln->nsm_clnt);
> +		status = nsm_mon_unmon(nsm, NSMPROC_UNMON, &res, host);
>  		if (res.status != 0)
>  			status = -EIO;
>  		if (status < 0)
> @@ -258,8 +201,6 @@ void nsm_unmonitor(const struct nlm_host *host)
>  					nsm->sm_name);
>  		else
>  			nsm->sm_monitored = 0;
> -
> -		nsm_client_put(host->net);
>  	}
>  }
>  
> diff --git a/fs/lockd/netns.h b/fs/lockd/netns.h
> index 89fe011..5426189 100644
> --- a/fs/lockd/netns.h
> +++ b/fs/lockd/netns.h
> @@ -12,9 +12,6 @@ struct lockd_net {
>  	struct delayed_work grace_period_end;
>  	struct lock_manager lockd_manager;
>  
> -	spinlock_t nsm_clnt_lock;
> -	unsigned int nsm_users;
> -	struct rpc_clnt *nsm_clnt;
>  	struct list_head nsm_handles;
>  };
>  
> diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
> index 0dff13f..5f31ebd 100644
> --- a/fs/lockd/svc.c
> +++ b/fs/lockd/svc.c
> @@ -592,7 +592,6 @@ static int lockd_init_net(struct net *net)
>  	INIT_DELAYED_WORK(&ln->grace_period_end, grace_ender);
>  	INIT_LIST_HEAD(&ln->lockd_manager.list);
>  	ln->lockd_manager.block_opens = false;
> -	spin_lock_init(&ln->nsm_clnt_lock);
>  	INIT_LIST_HEAD(&ln->nsm_handles);
>  	return 0;
>  }
> diff --git a/include/linux/lockd/lockd.h b/include/linux/lockd/lockd.h
> index fd3b65b..c153738 100644
> --- a/include/linux/lockd/lockd.h
> +++ b/include/linux/lockd/lockd.h
> @@ -68,6 +68,7 @@ struct nlm_host {
>  	struct nsm_handle	*h_nsmhandle;	/* NSM status handle */
>  	char			*h_addrbuf;	/* address eyecatcher */
>  	struct net		*net;		/* host net */
> +	char			nodename[UNX_MAXNODENAME + 1];
>  };
>  
>  /*
> -- 
> 2.4.9