Date: Fri, 18 Mar 2005 07:54:18 -0800
From: "Paul E. McKenney" <paulmck@us.ibm.com>
To: Bill Huey <bhuey@lnxw.com>
Cc: mingo@elte.hu, dipankar@in.ibm.com, shemminger@osdl.org, akpm@osdl.org,
       torvalds@osdl.org, rusty@au1.ibm.com, tgall@us.ibm.com,
       jim.houston@comcast.net, manfred@colorfullife.com, gh@us.ibm.com,
       linux-kernel@vger.kernel.org
Subject: Re: Real-Time Preemption and RCU
Message-ID: <20050318155418.GC1299@us.ibm.com>
Reply-To: paulmck@us.ibm.com
References: <20050318002026.GA2693@us.ibm.com> <20050318125641.GA5107@nietzsche.lynx.com>
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On Fri, Mar 18, 2005 at 04:56:41AM -0800, Bill Huey wrote:
> On Thu, Mar 17, 2005 at 04:20:26PM -0800, Paul E. McKenney wrote:
> > 5. Scalability -and- Realtime Response.
> ...
> 
> > 	void
> > 	rcu_read_lock(void)
> > 	{
> > 		preempt_disable();
> > 		if (current->rcu_read_lock_nesting++ == 0) {
> > 			current->rcu_read_lock_ptr =
> > 				&__get_cpu_var(rcu_data).lock;
> > 			read_lock(current->rcu_read_lock_ptr);
> > 		}
> > 		preempt_enable();
> > 	}
> 
> Ok, here's a rather unsure question...
> 
> Uh, is that a sleep violation if that is exclusively held since it
> can block within an atomic critical section (deadlock) ?

Hey, I wasn't joking when I said that I probably got something wrong!  ;-)

My current thought is that the preempt_disable()/preempt_enable() can
be dropped entirely.  Messes up any tool that browses through
->rcu_read_lock_nesting, but don't see any other problem.  Yet, anyway!

						Thanx, Paul
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