From: John Hubbard <jhubbard@nvidia.com>
To: Greg KH <gregkh@linuxfoundation.org>, Minchan Kim <minchan@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>, <surenb@google.com>,
<joaodias@google.com>, <willy@infradead.org>
Subject: Re: [PATCH v2] mm: cma: support sysfs
Date: Tue, 9 Feb 2021 12:11:20 -0800 [thread overview]
Message-ID: <09e60732-6a46-dd00-f9d5-4ef17ee685c8@nvidia.com> (raw)
In-Reply-To: <YCLLKDEQ4NYqb5Y5@kroah.com>
On 2/9/21 9:49 AM, Greg KH wrote:
>>> That's fine if you want to add it to the parent. If so, then the
>>> kobject controls the lifetime of the structure, nothing else can.
>>
>> The problem was parent object(i.e., struct cma cma_areas) is
>> static arrary so kobj->release function will be NULL or just
>> dummy. Is it okay? I thought it was one of the what you wanted
>> to avoid it.
>
> No, that is not ok.
>
>>> Either is fine with me, what is "forbidden" is having a kobject and
>>> somehow thinking that it does not control the lifetime of the structure.
>>
>> Since parent object is static arrary, there is no need to control the
>> lifetime so I am curious if parent object approach is okay from kobject
>> handling point of view.
>
> So the array is _NEVER_ freed? If not, fine, don't provide a release
> function for the kobject, but ick, just make a dynamic kobject I don't
> see the problem for something so tiny and not very many...
>
Yeah, I wasn't trying to generate so much discussion, I initially thought it
would be a minor comment: "just use an embedded struct and avoid some extra
code", at first.
> I worry that any static kobject might be copied/pasted as someone might
> think this is an ok thing to do. And it's not an ok thing to do.
>
Overall, then, we're seeing that there is a small design hole: in order
to use sysfs most naturally, you either much provide a dynamically allocated
item for it, or you must use the static kobject, and the second one sets a
bad example.
I think we should just use a static kobject, with a cautionary comment to
would-be copy-pasters, that explains the design constraints above. That way,
we still get a nice, less-code implementation, a safe design, and it only
really costs us a single carefully written comment.
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2021-02-09 20:11 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-08 18:01 [PATCH v2] mm: cma: support sysfs Minchan Kim
2021-02-08 21:34 ` John Hubbard
2021-02-08 23:36 ` Minchan Kim
2021-02-09 1:57 ` John Hubbard
2021-02-09 4:19 ` Minchan Kim
2021-02-09 5:18 ` John Hubbard
2021-02-09 5:27 ` John Hubbard
2021-02-09 6:13 ` Greg KH
2021-02-09 6:27 ` John Hubbard
2021-02-09 6:34 ` John Hubbard
2021-02-09 6:56 ` Greg KH
2021-02-09 15:55 ` Minchan Kim
2021-02-09 17:49 ` Greg KH
2021-02-09 20:11 ` John Hubbard [this message]
2021-02-09 21:13 ` Minchan Kim
2021-02-10 6:43 ` Greg KH
2021-02-10 7:12 ` Minchan Kim
2021-02-10 7:16 ` John Hubbard
2021-02-10 7:26 ` Greg KH
2021-02-10 7:50 ` John Hubbard
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