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

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Date:	Mon, 9 Sep 2013 18:18:19 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Eric Dumazet <eric.dumazet@...il.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, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, darren@...art.com,
	sbw@....edu, cl@...ux.com
Subject: Re: [PATCH] rcu: Is it safe to enter an RCU read-side critical
 section?

On Mon, Sep 09, 2013 at 06:53:20AM -0700, Paul E. McKenney wrote:
> On Mon, Sep 09, 2013 at 03:36:04PM +0200, Peter Zijlstra wrote:
> > On Mon, Sep 09, 2013 at 06:23:43AM -0700, Paul E. McKenney wrote:
> > > And guys, I have to say that the advice on which per-CPU primitive to use
> > > varies wildly and randomly.  For all I know, each of you individually
> > > might well be sticking to the same story, but taken together, your
> > > collective advice is strongly resembling white noise.
> > 
> > Its partly because cl and I disagree on things. He doesn't seem to care
> > much about validation and believes that people will not make mistakes
> > with this stuff.
> 
> At some point, my only recourse would be to require an Acked-by from one
> of you for any per-CPU changes proposed by the other.  I really hope that
> it doesn't come to that, but this situation is getting a bit annoying.

Nah, I'll not hold that over you. I think the current storm-in-teacup
was mostly due us seeing something suspicous and not understanding the
explanation well or so.

> > And partly because I didn't get what was going on. While Frederic's
> > explanation might be correct it was incomprehensible for me.
> 
> And I freely admit that the comments on rcu_is_cpu_idle() are completely
> inadequate, and I do apologize for that.  Seemed clear at the time.
> But then it always does, doesn't it?  ;-)

Yeah, I'm only all too familiar with this problem :/
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