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 12:40:44 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Peter Zijlstra <peterz@...radead.org>,
	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, 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 Mon, 9 Sep 2013 09:22:15 -0700
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:

> However, the API we are arguing about is deep within the implementation.
> It is not at the level of rcu_read_lock().  It is something that should
> not have that many invocations -- after all, the things using it are
> binding themselves unusually close to RCU.
> 

Is it? I guess the question is, is dynamic ticks an extension of RCU,
or is it just using the RCU implementation as a convenience?

Also the OP patch is for function tracing, something not coupled by RCU
at all. Just a way to know if it is safe to call functions that use RCU
or not.

That can have "this_cpu()" by the way as a way to tell us that we must
disable preemption before hand. Which is what caused this thread to
start with, as it was suggested to combine rcu_is_cpu_idle() which
brought up why that function disables preemption.

-- Steve
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