linux-kernel - Re: [PATCH RFC tip/core/rcu 1/2] rcu: suppress RCU lockdep warnings during early boot

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Date:	Tue, 2 Mar 2010 15:12:57 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com
Subject: Re: [PATCH RFC tip/core/rcu 1/2] rcu: suppress RCU lockdep warnings
 during early boot


* Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:

> On Tue, Mar 02, 2010 at 01:20:59PM +0100, Ingo Molnar wrote:
> > 
> > * Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
> > 
> > > +	if (!rcu_scheduler_active || !debug_locks)
> > > +		return 1;
> > > +	return lock_is_held(&rcu_lock_map);
> > 
> > > +	if (!rcu_scheduler_active || !debug_locks)
> > > +		return 1;
> > > +	return lock_is_held(&rcu_bh_lock_map);
> > 
> > i guess there could be a common helper here?
> 
> Will do!
> 
> > Also, could we clear rcu_scheduler_active when we clear debug_locks? That way 
> > only a single test is needed, a generic 'is lock debugging active'.
> 
> Doing that will break synchronize_rcu(), which returns immediately if
> !rcu_scheduler_active.

Ok - then have an debug_rcu flag which is cleared appropriately - so that the 
fastpath impact is reduced?

	Ingo
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