netdev - Re: [PATCH 6/13] bridge: Add core IGMP snooping support

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Date:	Tue, 9 Mar 2010 18:14:10 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Stephen Hemminger <shemminger@...tta.com>
Subject: Re: [PATCH 6/13] bridge: Add core IGMP snooping support

On Tue, Mar 09, 2010 at 10:12:59PM +0100, Arnd Bergmann wrote:
> On Sunday 07 March 2010, Paul E. McKenney wrote:
> > On Sun, Mar 07, 2010 at 10:45:00AM +0800, Herbert Xu wrote:
> > > On Sat, Mar 06, 2010 at 11:00:00AM -0800, Paul E. McKenney wrote:
> > 
> > Arnd, would it be reasonable to extend your RCU-sparse changes to have
> > four different pointer namespaces, one for each flavor of RCU?  (RCU,
> > RCU-bh, RCU-sched, and SRCU)?  Always a fan of making the computer do
> > the auditing where reasonable.  ;-)
> > 
> > This could potentially catch the mismatched call_rcu()s, at least if the
> > rcu_head could be labeled.
> > 
> > Other thoughts?
> 
> I've just tried annotating net/ipv4/route.c like this and did not get
> very far, because the same pointers are used for rcu and rcu_bh.
> Could you check if this is a false positive or an actual finding?

Hmmm...  I am only seeing a call_rcu_bh() here, so unless I am missing
something, this is a real problem in TREE_PREEMPT_RCU kernels.  The
call_rcu_bh() only interacts with the rcu_read_lock_bh() readers, not
the rcu_read_lock() readers.

One approach is to run freed blocks through both types of grace periods,
I suppose.

							Thanx, Paul
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