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

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Message-ID: <20200624135722.GF6578@ziepe.ca>
Date:   Wed, 24 Jun 2020 10:57:22 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Nicolas Boichat <drinkcat@...omium.org>
Cc:     linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        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>, dianders@...omium.org,
        groeck@...omium.org
Subject: Re: [PATCH] kernel/trace: Add TRACING_ALLOW_PRINTK config option

On Wed, Jun 24, 2020 at 04:45:24PM +0800, Nicolas Boichat 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>
>  include/linux/kernel.h | 17 ++++++++++++++++-
>  kernel/trace/Kconfig   |  9 +++++++++
>  2 files changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 196607aaf653082..b6addc6ba669e85 100644
> +++ b/include/linux/kernel.h
> @@ -721,10 +721,15 @@ do {									\
>  #define trace_printk(fmt, ...)				\
>  do {							\
>  	char _______STR[] = __stringify((__VA_ARGS__));	\
> +							\
> +	__static_assert(				\
> +		IS_ENABLED(CONFIG_TRACING_ALLOW_PRINTK),\
> +		"trace_printk called, please enable CONFIG_TRACING_ALLOW_PRINTK."); \
> +							\

Why __static_assert not normal static_assert?

Jason