Date: Fri, 18 Mar 2005 05:17:29 -0800
To: Bill Huey <bhuey@lnxw.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>, 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: <20050318131729.GB5107@nietzsche.lynx.com>
References: <20050318002026.GA2693@us.ibm.com> <20050318125641.GA5107@nietzsche.lynx.com>
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From: Bill Huey (hui) <bhuey@lnxw.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) ?

I'd like to note another problem. Mingo's current implementation of rt_mutex
(super mutex for all blocking synchronization) is still missing reader counts
and something like that would have to be implemented if you want to do priority
inheritance over blocks.

This is going to throw a wrench into your implementation if you assume that.

bill


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