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

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Date:   Tue, 31 Mar 2020 10:58:33 +0000
From:   "Sa, Nuno" <Nuno.Sa@...log.com>
To:     "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>,
        "lars@...afoo.de" <lars@...afoo.de>
Subject: RE: [PATCH 0/2] use DEFINE_DEBUGFS_ATTRIBUTE instead of
 DEFINE_SIMPLE_ATTRIBUTE

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...

- Nuno Sá
> > https://lkml.org/lkml/2019/10/30/144
> >
> > Has Greg KH raising the point that file reference counting is changed (as you
> > mention) but that can cause subtle bugs.  It 'might' be fine but is
> > definitely one that needs a tested-by from someone with the hardware.
> >
> > Jonathan