linux-kernel - Re: [RFC v1 08/14] bus1: implement peer management context

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Date:   Fri, 28 Oct 2016 15:23:02 +0200
From:   Tom Gundersen <teg@...m.no>
To:     Richard Weinberger <richard.weinberger@...il.com>
Cc:     David Herrmann <dh.herrmann@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, Greg KH <greg@...ah.com>,
        Hannes Reinecke <hare@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Arnd Bergmann <arnd@...db.de>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC v1 08/14] bus1: implement peer management context

On Fri, Oct 28, 2016 at 3:05 PM, Richard Weinberger
<richard.weinberger@...il.com> wrote:
> On Wed, Oct 26, 2016 at 9:18 PM, David Herrmann <dh.herrmann@...il.com> wrote:
>> +       /* initialize constant fields */
>> +       peer->id = atomic64_inc_return(&peer_ids);
>> +       peer->flags = 0;
>> +       peer->cred = get_cred(current_cred());
>> +       peer->pid_ns = get_pid_ns(task_active_pid_ns(current));
>> +       peer->user = user;
>> +       peer->debugdir = NULL;
>> +       init_waitqueue_head(&peer->waitq);
>> +       bus1_active_init(&peer->active);
>> +
>> +       /* initialize data section */
>> +       mutex_init(&peer->data.lock);
>> +
>> +       /* initialize peer-private section */
>> +       mutex_init(&peer->local.lock);
>> +
>> +       if (!IS_ERR_OR_NULL(bus1_debugdir)) {
>
> How can bus1_debugdir contain an error code? AFACT it is either a
> valid dentry or NULL.

If debugfs is not enabled it will be ERR_PTR(-ENODEV).

>> +               char idstr[22];
>> +
>> +               snprintf(idstr, sizeof(idstr), "peer-%llx", peer->id);
>> +
>> +               peer->debugdir = debugfs_create_dir(idstr, bus1_debugdir);
>> +               if (!peer->debugdir) {
>> +                       pr_err("cannot create debugfs dir for peer %llx\n",
>> +                              peer->id);
>> +               } else if (!IS_ERR_OR_NULL(peer->debugdir)) {
>> +                       bus1_debugfs_create_atomic_x("active", S_IRUGO,
>> +                                                    peer->debugdir,
>> +                                                    &peer->active.count);
>> +               }
>> +       }
>> +
>> +       bus1_active_activate(&peer->active);
>
> This is a no-nop since bus1_active_init() set ->count to BUS1_ACTIVE_NEW.

bus1_active_activate() changes count from BUS1_ACTIVE_NEW to 0.

>> +       return peer;
>> +}
>> +
>> +static int bus1_peer_disconnect(struct bus1_peer *peer)
>> +{
>> +       bus1_active_deactivate(&peer->active);
>> +       bus1_active_drain(&peer->active, &peer->waitq);
>> +
>> +       if (!bus1_active_cleanup(&peer->active, &peer->waitq,
>> +                                NULL, NULL))
>> +               return -ESHUTDOWN;
>> +
>> +       return 0;
>> +}
>> +
>> +/**
>> + * bus1_peer_free() - destroy peer
>> + * @peer:      peer to destroy, or NULL
>> + *
>> + * Destroy a peer object that was previously allocated via bus1_peer_new().
>> + * This synchronously waits for any outstanding operations on this peer to
>> + * finish, then releases all linked resources and deallocates the peer in an
>> + * rcu-delayed manner.
>> + *
>> + * If NULL is passed, this is a no-op.
>> + *
>> + * Return: NULL is returned.
>
> What about making the function of type void?

We are consistently returning the type being freed so we can do

foo->bar = bar_free(bar);

Just a matter of style though.

>> +struct bus1_peer *bus1_peer_free(struct bus1_peer *peer)
>> +{
>> +       if (!peer)
>> +               return NULL;
>> +
>> +       /* disconnect from environment */
>> +       bus1_peer_disconnect(peer);
>> +
>> +       /* deinitialize peer-private section */
>> +       mutex_destroy(&peer->local.lock);
>> +
>> +       /* deinitialize data section */
>> +       mutex_destroy(&peer->data.lock);
>> +
>> +       /* deinitialize constant fields */
>> +       debugfs_remove_recursive(peer->debugdir);
>> +       bus1_active_deinit(&peer->active);
>> +       peer->user = bus1_user_unref(peer->user);
>> +       put_pid_ns(peer->pid_ns);
>> +       put_cred(peer->cred);
>> +       kfree_rcu(peer, rcu);
>> +
>> +       return NULL;
>> +}
>
> --
> Thanks,
> //richard