linux-kernel - Re: [PATCH 0/2] use DEFINE_DEBUGFS_ATTRIBUTE instead of DEFINE_SIMPLE

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Date:   Tue, 31 Mar 2020 13:08:00 +0200
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     "Sa, Nuno" <Nuno.Sa@...log.com>,
        "Ardelean, Alexandru" <alexandru.Ardelean@...log.com>,
        "jic23@...nel.org" <jic23@...nel.org>,
        "rohitsarkar5398@...il.com" <rohitsarkar5398@...il.com>
Cc:     "stefan.popa@...log.com" <stefan.popa@...log.com>,
        "zhongjiang@...wei.com" <zhongjiang@...wei.com>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "Bogdan, Dragos" <Dragos.Bogdan@...log.com>,
        "pmeerw@...erw.net" <pmeerw@...erw.net>,
        "knaack.h@....de" <knaack.h@....de>,
        "Hennerich, Michael" <Michael.Hennerich@...log.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] use DEFINE_DEBUGFS_ATTRIBUTE instead of
 DEFINE_SIMPLE_ATTRIBUTE

On 3/31/20 12:58 PM, Sa, Nuno wrote:
> Hi Rohit,
>
>> From: linux-iio-owner@...r.kernel.org <linux-iio-owner@...r.kernel.org> On
>> Behalf Of Ardelean, Alexandru
>> Sent: Montag, 30. März 2020 11:20
>> To: jic23@...nel.org; rohitsarkar5398@...il.com
>> Cc: stefan.popa@...log.com; zhongjiang@...wei.com; linux-
>> iio@...r.kernel.org; Bogdan, Dragos <Dragos.Bogdan@...log.com>;
>> pmeerw@...erw.net; knaack.h@....de; Hennerich, Michael
>> <Michael.Hennerich@...log.com>; linux-kernel@...r.kernel.org;
>> lars@...afoo.de
>> Subject: Re: [PATCH 0/2] use DEFINE_DEBUGFS_ATTRIBUTE instead of
>> DEFINE_SIMPLE_ATTRIBUTE
>>
>> On Sun, 2020-03-29 at 10:38 +0100, Jonathan Cameron wrote:
>>> On Sat, 28 Mar 2020 12:04:53 +0530
>>> Rohit Sarkar <rohitsarkar5398@...il.com> wrote:
>>>
>>>> The debugfs_create_file_unsafe method does not protect the fops given to
>>>> it from file removal. It must be used with DEFINE_DEBUGFS_ATTRIBUTE
>>>> which makes the fops aware of the file lifetime.
>>>>
>>>> Further using DEFINE_DEBUGFS_ATTRIBUTE along with
>>>> debugfs_create_file_unsafe significantly reduces the overhead introduced
>> by
>>>> debugfs_create_file which creates a lifetime managing proxy around each
>>>> fops handed in. Refer [1] for more on this.
>>>>
>>>> Fixes the following warnings reported by coccinelle:
>>>> drivers/iio/imu//adis16460.c:126:0-23: WARNING:
>> adis16460_flash_count_fops
>>>> should be defined with DEFINE_DEBUGFS_ATTRIBUTE
>>>> drivers/iio/imu//adis16460.c:108:0-23: WARNING:
>> adis16460_product_id_fops
>>>> should be defined with DEFINE_DEBUGFS_ATTRIBUTE
>>>> drivers/iio/imu//adis16460.c:90:0-23: WARNING:
>> adis16460_serial_number_fops
>>>> should be defined with DEFINE_DEBUGFS_ATTRIBUTE
>>>> drivers/iio/imu//adis16400.c:278:0-23: WARNING:
>> adis16400_flash_count_fops
>>>> should be defined with DEFINE_DEBUGFS_ATTRIBUTE
>>>> drivers/iio/imu//adis16400.c:261:0-23: WARNING:
>> adis16400_product_id_fops
>>>> should be defined with DEFINE_DEBUGFS_ATTRIBUTE
>>>>
>>>> [1]: https://lists.gt.net/linux/kernel/2369498
>>>>
>>>> Rohit Sarkar (2):
>>>>    iio: imu: adis16400: use DEFINE_DEBUGFS_ATTRIBUTE instead of
>>>>      DEFINE_SIMPLE_ATTRIBUTE
>>>>    iio: imu: adis16460: use DEFINE_DEBUGFS_ATTRIBUTE instead of
>>>>      DEFINE_SIMPLE_ATTRIBUTE
>>>>
>>>>   drivers/iio/imu/adis16400.c | 4 ++--
>>>>   drivers/iio/imu/adis16460.c | 6 +++---
>>>>   2 files changed, 5 insertions(+), 5 deletions(-)
>>>>
>>> Hi Rohit,
>>>
>>> You've opened a can of worms with this one.  There as a previous series
>>> posted doing exactly this change back in 2019 by Zhong Jiang (cc'd)
>>>
>>> At the time I did a bit of looking into why this had been universally taken
>>> up cross tree and turned out there are some potential issues.
>>>
>>> Alexandru added it to the list of things to test, but I guess it got
>>> buried under other work and is still outstanding.
>>>
>> yep
>> my bad;
>> will try to make room these days for that old one
>>
>>
> I don't have the exact parts that this patch is touching but I have other parts where this patch
> applies and should be same. So, the idea to test this is to read the files in debugfs? Maybe also
> some unbind + binding?
>
> I will try to test this still today...

The stress test is to open the debugfs file, then unbind the device and 
then read from the still open debugfs file.

- Lars