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

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Message-ID: <20130911152331.GZ3966@linux.vnet.ibm.com>
Date:	Wed, 11 Sep 2013 08:23:31 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	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 Wed, Sep 11, 2013 at 10:26:07AM -0400, Steven Rostedt wrote:
> On Wed, 11 Sep 2013 07:13:02 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > On Mon, Sep 09, 2013 at 03:34:26PM -0700, Paul E. McKenney wrote:
> > > On Mon, Sep 09, 2013 at 05:59:17PM -0400, Steven Rostedt wrote:
> > > > On Mon, 9 Sep 2013 17:40:26 -0400
> > > > Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
> > > > 
> > > > > Agreed. So how about rcu_is_online() ?
> > > > 
> > > > Nope, what about all_your_base_are_belong_to_rcu()?
> > > 
> > > Let's see if I can remember the candidates...
> > > 
> > > 	rcu_is_cpu_idle() # reversed sense from the others
> > > 	rcu_is_ignored() # reversed sense from the others
> > > 	rcu_is_not_active() # reversed sense from the others
> > > 	rcu_is_watching_cpu()
> > > 	rcu_read_check()
> > > 	rcu_is_active()
> > > 	rcu_is_active_local()
> > > 	rcu_is_online()
> > > 	rcu_is_watching_task()
> > > 	rcu_is_watching_thread()
> > > 	rcu_is_watching_you()
> > > 	all_your_base_are_belong_to_rcu()
> > > 	rcu_is_active_loco()
> > > 	rcu_kilroy_was_here()
> > > 
> > > Maybe I should just lock them all in a room overnight and see which
> > > are still alive in the morning.
> > 
> > And after treating injuries, the survivor is rcu_is_watching().
> > 
> 
> But, but, but...
> 
> That wasn't one of the contenders!
> 
> What happened? Did rcu_is_watching_cpu(), rcu_is_watching_task(),
> rcu_is_watching_thread() and rcu_is_watching_you() all get together to
> gang up on the others, and then combined to be one?
> 
> It's another Iraq! Several segments joined together by an outside
> force and they don't play well together. And like Iraq (and the US),
> hidden inside of this "community" is "rcu_is_watching_you"!

C'mon, Steven!  I did say "after treating injuries"!  In the opinion
of the surgeon, the only option was to ampute what was left of either
the _cpu(), _task(), _thread(), or _you().  Heck, the damage was so
severe that we couldn't even tell which one it was!

							Thanx, Paul

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