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

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Message-ID: <20100302145544.GA6786@linux.vnet.ibm.com>
Date:	Tue, 2 Mar 2010 06:55:45 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
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

On Tue, Mar 02, 2010 at 03:12:57PM +0100, Ingo Molnar wrote:
> 
> * 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?

Good point, will do!

							Thanx, Paul
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