Re: [PATCH v4 3/3] media: atomisp: Only use trace_printk if allowed

[Steven Rostedt]

On Thu, 20 Aug 2020 19:36:19 -0700
Joe Perches <joe@xxxxxxxxxxx> 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@xxxxxxxxxxxx> 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