linux-kernel - Re: [PATCH RFC 6/9] RCU priority boosting for preemptible RCU

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Message-ID: <Pine.LNX.4.58.0709281901470.17405@gandalf.stny.rr.com>
Date:	Fri, 28 Sep 2007 19:05:14 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Gautham R Shenoy <ego@...ibm.com>
cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, akpm@...ux-foundation.org,
	dipankar@...ibm.com, josht@...ux.vnet.ibm.com, tytso@...ibm.com,
	dvhltc@...ibm.com, Thomas Gleixner <tglx@...utronix.de>,
	a.p.zijlstra@...llo.nl, bunk@...nel.org, oleg@...sign.ru,
	srostedt@...hat.com
Subject: Re: [PATCH RFC 6/9] RCU priority boosting for preemptible RCU



--
On Fri, 28 Sep 2007, Gautham R Shenoy wrote:

> >
> > +#ifdef CONFIG_PREEMPT_RCU_BOOST
> > +/*
> > + * Task state with respect to being RCU-boosted.  This state is changed
> > + * by the task itself in response to the following three events:
> 							^^^
> > + * 1. Preemption (or block on lock) while in RCU read-side critical section.
>
> I am wondering, can a task block on a lock while in RCU read-side
> critical section?

I think this may be specific to the -rt patch. In the -rt patch,
spin_locks turn into mutexes, and therefor can block a read-side critical
section.


> > + * 2. Outermost rcu_read_unlock() for blocked RCU read-side critical section.
> > + *
>
> Event #3. is missing?

I guess Paul needs to answer that one ;-)

-- Steve

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