linux-kernel - Re: [PATCH v4 3/3] media: atomisp: Only use trace

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Date:   Thu, 20 Aug 2020 22:44:59 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Nicolas Boichat <drinkcat@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        devel@...verdev.osuosl.org, lkml <linux-kernel@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Douglas Anderson <dianders@...omium.org>,
        Guenter Roeck <groeck@...omium.org>
Subject: Re: [PATCH v4 3/3] media: atomisp: Only use trace_printk if allowed

On Thu, 20 Aug 2020 19:36:19 -0700
Joe Perches <joe@...ches.com> wrote:

> On Thu, 2020-08-20 at 21:57 -0400, Steven Rostedt wrote:
> > On Fri, 21 Aug 2020 09:39:19 +0800
> > Nicolas Boichat <drinkcat@...omium.org> wrote:  
> []
> > > Some other approaches/ideas:
> > >  1. Filter all lkml messages that contain trace_printk. Already found
> > > 1 instance, and I can easily reply to those with a semi-canned answer,
> > > if I remember to check that filter regularly (not sustainable in the
> > > long run...).  
> > 
> > Added Joe Perches to the thread.
> > 
> > We can update checkpatch.pl to complain about a trace_printk() that it
> > finds in the added code.  
> 
> Why?
> 
> I don't see much value in a trace_printk checkpatch warning.
> tracing is still dependent on CONFIG_TRACING otherwise
> trace_printk is an if (0)
> 
> ELI5 please.
> 

Because no production code should contain trace_printk(). It should be
deleted before going to Linus. If you have trace_printk() in your code,
you will be greeted by the following banner in your dmesg:

 **********************************************************
 **   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 you see this message and you are not debugging    **
 ** the kernel, report this immediately to your vendor!  **
 **                                                      **
 **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
 **********************************************************

-- Steve