linux-kernel - Re: [PATCH 07/10] printk: Remove the now superfluous sentinel elements from ctl

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Date:   Wed, 6 Dec 2023 10:55:51 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Joel Granados <j.granados@...sung.com>
Cc:     Luis Chamberlain <mcgrof@...nel.org>, willy@...radead.org,
        josh@...htriplett.org, Kees Cook <keescook@...omium.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <jstultz@...gle.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
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        John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
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        Balbir Singh <bsingharora@...il.com>,
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        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH 07/10] printk: Remove the now superfluous sentinel
 elements from ctl_table array

On Mon 2023-12-04 09:56:28, Joel Granados wrote:
> Hey Petr
> 
> I missed this message somehow....
> 
> On Tue, Nov 28, 2023 at 03:07:43PM +0100, Petr Mladek wrote:
> > On Tue 2023-11-07 14:45:07, Joel Granados via B4 Relay wrote:
> > > From: Joel Granados <j.granados@...sung.com>
> > > 
> > > This commit comes at the tail end of a greater effort to remove the
> > > empty elements at the end of the ctl_table arrays (sentinels) which
> > > will reduce the overall build time size of the kernel and run time
> > > memory bloat by ~64 bytes per sentinel (further information Link :
> > > https://lore.kernel.org/all/ZO5Yx5JFogGi%2FcBo@bombadil.infradead.org/)
> > > 
> > > rm sentinel element from printk_sysctls
> > > 
> > > Signed-off-by: Joel Granados <j.granados@...sung.com>
> > 
> > I am a bit sceptical if the size and time reduction is worth the
> > effort. I feel that this change makes the access a bit less secure.
> In what way "less secure"? Can you expand on that?
> 
> Notice that if you pass a pointer to the register functions, you will
> get a warning/error on compilation.

I have vague memories that some arrays were not static or the length
has been somehow manipulated. But I might be wrong.

You are right that it should be safe with the static arrays.
And the NULL sentinel might be more error-prone after all.

Let's forget my mumbles.

Best Regards,
Petr