linux-kernel - Re: [RFC][PATCH RT] rcu,rt: Allow rcu_read_lock

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Message-ID: <1372259103.18733.260.camel@gandalf.local.home>
Date:	Wed, 26 Jun 2013 11:05:03 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Clark Williams <clark@...hat.com>
Subject: Re: [RFC][PATCH RT] rcu,rt: Allow rcu_read_lock_sched() to schedule

On Wed, 2013-06-26 at 11:03 -0400, Steven Rostedt wrote:

> > I tried this approach in early 2005, and testing did not go well:
> > 
> > https://lkml.org/lkml/2005/3/17/199
> > 
> > For one thing, a lock acquired both within and surrounding an
> > RCU-sched read-side critical section would result in deadlock.
> > 
> > Or have things changed so that this now somehow works?
> 
> Well, so far lockdep hasn't splatted on this. But that's not saying much
> because I'm currently fighting the lockdep splats from other workqueue
> related stuff.
> 
> Seems that Tejun really doesn't like us RT folks ;-)

If there are issues, we could make a rcu_read_lock_sched_rt() which for
mainline will be rcu_read_lock_sched(), but for -rt will grab the lock.
That way we can pick and choose the locations that this is required.

-- Steve


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