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

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Date:   Fri, 28 Oct 2016 15:18:59 +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 2:06 PM, Richard Weinberger
<richard.weinberger@...il.com> wrote:
> David, Tom,
>
> On Wed, Oct 26, 2016 at 9:18 PM, David Herrmann <dh.herrmann@...il.com> wrote:
>> +struct bus1_peer *bus1_peer_new(void)
>> +{
>> +       static atomic64_t peer_ids = ATOMIC64_INIT(0);
>> +       const struct cred *cred = current_cred();
>> +       struct bus1_peer *peer;
>> +       struct bus1_user *user;
>> +
>> +       user = bus1_user_ref_by_uid(cred->uid);
>> +       if (IS_ERR(user))
>> +               return ERR_CAST(user);
>> +
>> +       peer = kmalloc(sizeof(*peer), GFP_KERNEL);
>> +       if (!peer) {
>> +               bus1_user_unref(user);
>> +               return ERR_PTR(-ENOMEM);
>> +       }
>> +
>> +       /* initialize constant fields */
>> +       peer->id = atomic64_inc_return(&peer_ids);
>
> What is the purpose of this id? Do other components depend on it
> and are they aware of possible overflows?

The id is used purely to give a name to the peer in debugfs.

> Since it is an 64bit integer overflowing it is hard but not impossible.

Hm, what scenario do you have in mind? I cannot see how this could
happen (short of creating peers in a loop for hundreds of years).

Cheers,

Tom