linux-kernel - RE: [PATCH v5] kernel/trace: Add DISALLOW_TRACE

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Message-ID: <3f84781f12424cbfa552981af42dfaf2@AcuMS.aculab.com>
Date:   Mon, 24 Aug 2020 08:26:13 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Nicolas Boichat' <drinkcat@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>
CC:     "dianders@...omium.org" <dianders@...omium.org>,
        "groeck@...omium.org" <groeck@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        "Guilherme G. Piccoli" <gpiccoli@...onical.com>,
        Kars Mulder <kerneldev@...smulder.nl>,
        Kees Cook <keescook@...omium.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Will Deacon <will@...nel.org>, Yue Hu <huyue2@...ong.com>,
        "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v5] kernel/trace: Add DISALLOW_TRACE_PRINTK make option

From: Nicolas Boichat
> Sent: 24 August 2020 03:59
> 
> 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.

Since the objective seems to be to ensure there are no
calls to trace_printk() in the git tree, but to allow
them in uncommitted sources. Why not use a config option
and rely on rand-config builds to detect any 'accidental'
commits?

	David

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