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

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Message-ID: <20070930031131.GF9119@linux.vnet.ibm.com>
Date:	Sat, 29 Sep 2007 20:11:31 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Gautham R Shenoy <ego@...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, Sep 28, 2007 at 07:05:14PM -0400, Steven Rostedt wrote:
> 
> 
> --
> 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.

Yep!  I do need to fix the comment.

> > > + * 2. Outermost rcu_read_unlock() for blocked RCU read-side critical section.
> > > + *
> >
> > Event #3. is missing?
> 
> I guess Paul needs to answer that one ;-)

An older version had three, the new one has two, and I forgot to s/three/two/.

							Thanx, Paul
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