linux-kernel - Re: [PATCH] kernel/trace: Add TRACING_ALLOW

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Message-ID: <CANMq1KAVXvMJpNXQoBPMPmSF=vPphvCC_SCFsX03CkR6PY7AKA@mail.gmail.com>
Date:   Thu, 25 Jun 2020 09:32:19 +0800
From:   Nicolas Boichat <drinkcat@...omium.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Peter Zijlstra <peterz@...radead.org>,
        Vinod Koul <vkoul@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Guilherme G . Piccoli" <gpiccoli@...onical.com>,
        Will Deacon <will@...nel.org>,
        Douglas Anderson <dianders@...omium.org>,
        Guenter Roeck <groeck@...omium.org>
Subject: Re: [PATCH] kernel/trace: Add TRACING_ALLOW_PRINTK config option

On Thu, Jun 25, 2020 at 12:04 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Wed, 24 Jun 2020 16:45:24 +0800
> Nicolas Boichat <drinkcat@...omium.org> wrote:
>
> > trace_printk is only meant as a debugging tool, and should never be
> > compiled into production code without source code changes, as
> > indicated by the warning that shows up on boot if any trace_printk
> > is called:
> >  **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
> >  **                                                      **
> >  ** trace_printk() being used. Allocating extra memory.  **
> >  **                                                      **
> >  ** This means that this is a DEBUG kernel and it is     **
> >  ** unsafe for production use.                           **
> >
> > If this option is set to n, the kernel will generate a build-time
> > error if trace_printk is used.
> >
> > Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
>
> Interesting. Note, this will prevent modules with trace_printk from
> being loaded as well.

Err, all of these changes are in macros (nothing gets built in the
kernel), so this will prevent modules with trace_printk from being
_built_.

Now, if you set the option to =y when building the module (separately,
even though the rest of the kernel has =n) then I don't see why the
module could not be loaded.

>
> -- Steve