linux-kernel - Re: [PATCH v9 5/7] tracing: Centralize preemptirq tracepoints and unify their usage

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Date:   Wed, 11 Jul 2018 09:22:34 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, Boqun Feng <boqun.feng@...il.com>,
        Byungchul Park <byungchul.park@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Julia Cartwright <julia@...com>,
        linux-kselftest@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Thomas Glexiner <tglx@...utronix.de>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>
Subject: Re: [PATCH v9 5/7] tracing: Centralize preemptirq tracepoints and
 unify their usage

On Wed, 11 Jul 2018 09:19:44 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Wed, 11 Jul 2018 15:12:56 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Thu, Jun 28, 2018 at 11:21:47AM -0700, Joel Fernandes wrote:  
> > > One note, I have to check for lockdep recursion in the code that calls
> > > the trace events API and bail out if we're in lockdep recursion    
> > 
> > I'm not seeing any new lockdep_recursion checks...  
> 
> I believe he's talking about this part:
> 
> +void trace_hardirqs_on(void)
> +{
> +	if (lockdep_recursing(current) || !this_cpu_read(tracing_irq_cpu))
> +		return;
> +

And the reason he said this is new, IIUC, is because the old way we
could still do irqsoff tracing even if lockdep_recursion is set. Now,
irqsoff tracing is disable within lockdep_recursion.

-- Steve