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From:   Nicolas Boichat <drinkcat@chromium.org>
Date:   Thu, 25 Jun 2020 09:13:17 +0800
Message-ID: <CANMq1KB1W77JATT0NmGpKeCCpWrXraoDAH5SgGMgBESRynTBJQ@mail.gmail.com>
Subject: Re: [PATCH] kernel/trace: Add TRACING_ALLOW_PRINTK config option
To:     Jason Gunthorpe <jgg@ziepe.ca>
Cc:     lkml <linux-kernel@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Peter Zijlstra <peterz@infradead.org>,
        Vinod Koul <vkoul@kernel.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Tiezhu Yang <yangtiezhu@loongson.cn>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Guilherme G . Piccoli" <gpiccoli@canonical.com>,
        Will Deacon <will@kernel.org>,
        Douglas Anderson <dianders@chromium.org>,
        Guenter Roeck <groeck@chromium.org>
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Sender: linux-kernel-owner@vger.kernel.org
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On Wed, Jun 24, 2020 at 9:57 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
>
> 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@chromium.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?

Oh, I misread the macro code (and didn't read the comment above in
include/linux/build_bug.h). static_assert would be just fine.

>
> Jason