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

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Message-ID: <1372268409.18733.264.camel@gandalf.local.home>
Date:	Wed, 26 Jun 2013 13:40:09 -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 11:05 -0400, Steven Rostedt wrote:
> 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.
> 

I finally fixed the other issues and ran a full compile on this kernel.
No problems appeared yet, so maybe things have changed.

-- Steve


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