linux-kernel - Re: [PATCH] rcu: Is it safe to enter an RCU read-side critical section?

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Message-ID: <20130906170006.GC2706@somewhere>
Date:	Fri, 6 Sep 2013 19:00:08 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, dhowells@...hat.com, edumazet@...gle.com,
	darren@...art.com, sbw@....edu
Subject: Re: [PATCH] rcu: Is it safe to enter an RCU read-side critical
 section?

On Fri, Sep 06, 2013 at 12:52:38PM -0400, Steven Rostedt wrote:
> On Fri, 6 Sep 2013 18:40:18 +0200
> Frederic Weisbecker <fweisbec@...il.com> wrote:
>  
> > > I can't use plain preempt_disable() in function tracing.
> > > 
> > > Also, since it's a misnomer to say the cpu is idle in NO_HZ_FULL when
> > > we are coming from userspace, can we rename that?
> > > 
> > > Perhaps we can also have a __rcu_is_cpu_tracking() (or whatever), with
> > > the "__" appended that does not do the preempt disable.
> > 
> > rcu_is_cpu_eqs() is probably better. It refers to other related "eqs" naming
> > in RCU APIs.
> 
> But that will just confuse the heck out of people. When I see "eqs" I
> equate that with "equals". What does the rcu cpu equal?

It's "extended quiescent state". There is already rcu_eqs_enter() and rcu_eqs_exit().
You're right, may be we can rename that to avoid confusion with "equals". I don't mind much.
I'm happy as long as the reader rcu_is_cpu_foo() and the writers rcu_foo_enter() and
rcu_foo_exit() have consistant naming.

> 
> -- Steve
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