linux-kernel - Re: possible circular locking dependency

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Date:	Sun, 6 May 2012 20:47:49 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Dave Jones <davej@...hat.com>
Subject: Re: possible circular locking dependency

On Sun, May 06, 2012 at 11:34:39PM +0300, Sergey Senozhatsky wrote:
> On (05/06/12 09:42), Paul E. McKenney wrote:
> > On Sun, May 06, 2012 at 11:55:30AM +0300, Avi Kivity wrote:
> > > On 05/03/2012 11:02 PM, Sergey Senozhatsky wrote:
> > > > Hello,
> > > > 3.4-rc5
> > > 
> > > Whoa.
> > > 
> > > Looks like inconsistent locking between cpufreq and
> > > synchronize_srcu_expedited().  kvm triggered this because it is one of
> > > the few users of synchronize_srcu_expedited(), but I don't think it is
> > > doing anything wrong directly.
> > > 
> > > Dave, Paul?
> > 
> > SRCU hasn't changed much in mainline for quite some time.  Holding
> > the hotplug mutex across a synchronize_srcu() is a bad idea, though.
> > 
> > However, there is a reworked implementation (courtesy of Lai Jiangshan)
> > in -rcu that does not acquire the hotplug mutex.  Could you try that out?
> >
> 
> Paul, should I try solely -rcu or there are several commits to pick up and apply
> on top of -linus tree?

If you want the smallest possible change, take the rcu/srcu branch of -rcu.
If you want the works, take the rcu/next branch of -rcu.

You can find -rcu at:

git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git

								Thanx, Paul

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