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

From: J. Bruce Fields
Date: Wed Oct 07 2015 - 16:41:27 EST

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@xxxxxxxxxxxxx>
> ---
> 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
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