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Date:   Mon, 28 Sep 2020 11:26:46 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     Nicolas Boichat <drinkcat@chromium.org>, groeck@chromium.org,
        dianders@chromium.org, Andrew Morton <akpm@linux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        "Guilherme G. Piccoli" <gpiccoli@canonical.com>,
        Kars Mulder <kerneldev@karsmulder.nl>,
        Kees Cook <keescook@chromium.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Rafael Aquini <aquini@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will@kernel.org>, linux-kbuild@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6] kernel/trace: Add DISALLOW_TRACE_PRINTK make option
Message-ID: <20200928112646.4968999c@oasis.local.home>
In-Reply-To: <20200928152840.v6.1.I4feb11d34ce7a0dd5ee2c3327fb5a1a9a646be30@changeid>
References: <20200928152840.v6.1.I4feb11d34ce7a0dd5ee2c3327fb5a1a9a646be30@changeid>
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On Mon, 28 Sep 2020 15:29:29 +0800
Nicolas Boichat <drinkcat@chromium.org> wrote:

> trace_printk is meant as a debugging tool, and should not be
> compiled into production code without specific debug Kconfig
> options enabled, or 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 DISALLOW_TRACE_PRINTK=1 is passed on the make command
> line, the kernel will generate a build-time error if
> trace_printk is used. We expect distributors to set this
> option for their production kernels.
> 
> Note that the code to handle trace_printk is still present,
> so this does not prevent people from compiling out-of-tree
> kernel modules, or BPF programs.
> 
> Also, we are not making this a kernel config option as we
> want the developer convenience of being able to reuse a
> production kernel config, add trace_printk for debugging,
> and rebuild, without any config changes.
> 
> Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>

Masahiro,

Are you OK with this change? If so can I have your Ack?

-- Steve