linux-kernel - Re: async pf: INFO: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected

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Message-ID: <20120427181450.GF2534@linux.vnet.ibm.com>
Date:	Fri, 27 Apr 2012 11:14:50 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	Gleb Natapov <gleb@...hat.com>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
	kvm@...r.kernel.org
Subject: Re: async pf: INFO: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order
 detected

On Fri, Apr 27, 2012 at 08:05:15PM +0200, Sasha Levin wrote:
> On Fri, Apr 27, 2012 at 5:23 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> >
> > On Thu, Apr 26, 2012 at 04:50:35PM +0200, Sasha Levin wrote:
> > > Hi all.
> > >
> > > I got a "INFO: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected"
> > > warning
> > > while running LTP inside a KVM guest using the recent -next kernel.
> > >
> > > It seems that it was initially originated from rcu_torture_rea(), but I
> > > don't think that it's a problem with RCU itself (I'll cc. Paul just in
> > > case). RCU torture was indeed configured to run during the testing.
> >
> > I might be missing something, but I don't see how RCU is involved in
> > this one.
> 
> It happened due to a rcutorture thread:
> 
> [ 4248.579019] rcu_torture_rea/1615 [HC0[0]:SC0[0]:HE0:SE1] is trying
> to acquire:
> [ 4248.579019]  (pgd_lock){+.+...}, at: [<ffffffff81089476>] pgd_free+0x26/0xa0
> 
> rcutorture has never triggered anything on my tests up until now, and
> is probably not responsible for the actual warning in this case, just
> figured I should cc you in case I'm wrong :)

No worries!

I only responded on the off-chance that everyone else was waiting on
me to identify the bug and provide the fix.  ;-)

							Thanx, Paul

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