linux-kernel - Re: [PATCH v2 3/9] rcu,tracing: Create trace_rcu

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Message-ID: <20200213183914.GB207225@google.com>
Date:   Thu, 13 Feb 2020 13:39:14 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        rostedt@...dmis.org, mingo@...nel.org, gregkh@...uxfoundation.org,
        gustavo@...eddedor.com, tglx@...utronix.de, paulmck@...nel.org,
        josh@...htriplett.org, mathieu.desnoyers@...icios.com,
        jiangshanlai@...il.com
Subject: Re: [PATCH v2 3/9] rcu,tracing: Create trace_rcu_{enter,exit}()

On Thu, Feb 13, 2020 at 09:28:14AM +0100, Peter Zijlstra wrote:
> On Wed, Feb 12, 2020 at 06:27:02PM -0500, Joel Fernandes wrote:
> > On Wed, Feb 12, 2020 at 10:01:42PM +0100, Peter Zijlstra wrote:
> 
> > > +#define trace_rcu_enter()					\
> > > +({								\
> > > +	unsigned long state = 0;				\
> > > +	if (!rcu_is_watching())	{				\
> > > +		if (in_nmi()) {					\
> > > +			state = __TR_NMI;			\
> > > +			rcu_nmi_enter();			\
> > > +		} else {					\
> > > +			state = __TR_IRQ;			\
> > > +			rcu_irq_enter_irqsave();		\
> > 
> > Since rcu_irq_enter_irqsave can be called from a tracer context, should those
> > be marked with notrace as well? AFAICS, there's no notrace marking on them.
> 
> It should work, these functions are re-entrant (as are IRQs / NMIs) and
> Steve wants to be able to trace RCU itself.

Hoping there are no recursion scenarios possible, but that sounds good to me. thanks,

 - Joel