linux-kernel - Re: [PATCH] ARM: imx_v6_v7_defconfig: Explicitly restore CONFIG_DEBUG

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Date:   Wed, 11 Dec 2019 19:02:01 +0000
From:   Leonard Crestez <leonard.crestez@....com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>
CC:     Shawn Guo <shawnguo@...nel.org>,
        Fabio Estevam <fabio.estevam@....com>,
        Aisheng Dong <aisheng.dong@....com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Kusanagi Kouichi <slash@...auone-net.jp>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        dl-linux-imx <linux-imx@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: imx_v6_v7_defconfig: Explicitly restore
 CONFIG_DEBUG_FS

On 10.12.2019 22:45, Greg Kroah-Hartman wrote:
> On Tue, Dec 10, 2019 at 07:34:20PM +0200, Leonard Crestez wrote:
>> This is currently off and that's not desirable: default imx config is
>> meant to be generally useful for development and debugging.
>>
>> Running git bisect between v5.4 and v5.5-rc1 finds this started from
>> commit 0e4a459f56c3 ("tracing: Remove unnecessary DEBUG_FS dependency")
>>
>> Explicit CONFIG_DEBUG_FS=y was earlier removed by
>> commit c29d541f590c ("ARM: imx_v6_v7_defconfig: Remove unneeded options")
>>
>> A very similar fix was required before:
>> commit 7e9eb6268809 ("ARM: imx_v6_v7_defconfig: Explicitly restore CONFIG_DEBUG_FS")
>>
>> Signed-off-by: Leonard Crestez <leonard.crestez@....com>
>> ---
>>   arch/arm/configs/imx_v6_v7_defconfig | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> Any suggestions to prevent such unexpected kconfig changes in the
>> future? It might make sense for DEBUG_FS to be "default y".
> 
> What?  No, no system functionality should _EVER_ be dependant on debugfs
> being enabled at all.
> 
> If your kernel code requires this, then you are doing something really
> really really wrong.
> 
> Now if you just want to have a nice debugging system, then sure, enable
> the option, but it is not anything that should ever be required by any
> working system.

I just want a nice debugging system, my concern is that kconfig rule 
adjustments sometimes unexpectedly break this. This issues apparently 
also affected shmobile: https://patchwork.kernel.org/patch/11278961/

Config options which can be manually controlled but are also "selected" 
from a whole bunch of places can get lost after savedefconfig

Would it be reasonable to make all users "depend on" rather than 
"select" DEBUG_FS?

Or perhaps DEBUG_FS could be "default y if DEBUG_KERNEL"?

--
Regards,
Leonard