linux-kernel - Re: [PATCH] device-dax: don't set kobj parent during cdev init

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Message-ID: <CAPcyv4g3KO8W0T9aNCB=Z40Zk4OF_SVz3jOb3fGfM6eE6M-VgA@mail.gmail.com>
Date:   Sat, 11 Feb 2017 10:55:26 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Sajjan Vikas C <vikas.cha.sajjan@....com>,
        Arnd Bergmann <arnd@...db.de>, Jan Kara <jack@...e.cz>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: Re: [PATCH] device-dax: don't set kobj parent during cdev init

On Sat, Feb 11, 2017 at 10:43 AM, Logan Gunthorpe <logang@...tatee.com> wrote:
>
> On 11/02/17 11:27 AM, Dan Williams wrote:
>> Why, when the lifetime of the cdev is already correct?
>
> Well, it's only correct if you use the kobj parent trick which Greg is
> arguing against. As someone reviewing/copying code that trick is
> unclear, undocumented and it looks rather odd messing with internal
> kobjects. Taking the explicit reference would be very clear, very
> standard and only net one additional line.
>
>> See commit ba09c01d2fa8 "dax: convert to the cdev api". I used to take
>> explicit references like you suggest, but cdev made it cleaner.
>
> I agree that, on the whole, that patch makes things a good deal cleaner.
> I'm not so sure that this one small aspect is an improvement.
>
> In any case, it's up to you. If you'd like I can certainly submit a v2
> patch that adds the get/put.

Can we meet in the middle and just add some comments about what is going on?

It's a shame to add reference counts for something that is already
properly reference counted.