linux-kernel - Re: [PATCH V3 8/9] tracing: Add osnoise tracer

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Date:   Tue, 8 Jun 2021 13:39:46 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Phil Auld <pauld@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Kate Carcia <kcarcia@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Clark Willaims <williams@...hat.com>,
        John Kacur <jkacur@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>, linux-doc@...r.kernel.org
Subject: Re: [PATCH V3 8/9] tracing: Add osnoise tracer

On Tue, 8 Jun 2021 19:17:55 +0200
Daniel Bristot de Oliveira <bristot@...hat.com> wrote:

> On 6/4/21 11:28 PM, Steven Rostedt wrote:
> >> +	/*
> >> +	 * This is an evidence of race conditions that cause
> >> +	 * a value to be "discounted" too much.
> >> +	 */
> >> +	if (duration < 0)
> >> +		pr_err("int safe negative!\n");  
> > Probably want to have this happen at most once a run. If something were
> > to break, I don't think we want this to live lock the machine doing
> > tons of prints. We could have a variable stored on the
> > osnoise_variables that states this was printed. Check that variable to
> > see if it wasn't printed during a run (when current_tracer was set),
> > and print only once if it is.  
> 
> I created a "bool tainted" variable, that is set true if any problem with time()
> related functions happen. I will pr_warn that there is a problem on _start(),
> but also print this info at the top of the tracer header, so it is clear also
> from the trace output.
> 
> Thoughts?
>

Or perhaps have that pr_err() actually be written into the trace buffer?

You can use

	trace_array_printk_buf(tr->array_buffer.buffer, _THIS_IP_, "string");

without it triggering that nasty trace_printk() notice ;-)

-- Steve