linux-kernel - Re: [PATCH tip/core/rcu 04/18] rcu: Use single-stage IPI algorithm for RCU expedited grace period

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Date:	Wed, 7 Oct 2015 11:11:17 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	jiangshanlai@...il.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH tip/core/rcu 04/18] rcu: Use single-stage IPI algorithm
 for RCU expedited grace period

On Wed, Oct 07, 2015 at 03:24:54PM +0200, Peter Zijlstra wrote:
> On Tue, Oct 06, 2015 at 09:29:23AM -0700, Paul E. McKenney wrote:
> > @@ -3494,19 +3483,21 @@ static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
> >   * recursively up the tree.  (Calm down, calm down, we do the recursion
> >   * iteratively!)
> >   *
> > - * Caller must hold the root rcu_node's exp_funnel_mutex.
> > + * Caller must hold the root rcu_node's exp_funnel_mutex and the
> > + * specified rcu_node structure's ->lock.
> >   */
> > -static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,
> > -					      struct rcu_node *rnp, bool wake)
> > +static void __rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
> > +				 bool wake, unsigned long flags)
> > +	__releases(rnp->lock)
> >  {
> > -	unsigned long flags;
> >  	unsigned long mask;
> >  
> > -	raw_spin_lock_irqsave(&rnp->lock, flags);
> > -	smp_mb__after_unlock_lock();
> 
> 	lockdep_assert_held(&rnp->lock);
> 
> > +/*
> > + * Report expedited quiescent state for specified node.  This is a
> > + * lock-acquisition wrapper function for __rcu_report_exp_rnp().
> > + *
> > + * Caller must hold the root rcu_node's exp_funnel_mutex.
> > + */
> > +static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,
> > +					      struct rcu_node *rnp, bool wake)
> > +{
> > +	unsigned long flags;
> 
> 	lockdep_assert_held(&rcu_get_root(rsp)->exp_funnel_mutex);
> 
> > +
> > +	raw_spin_lock_irqsave(&rnp->lock, flags);
> > +	smp_mb__after_unlock_lock();
> > +	__rcu_report_exp_rnp(rsp, rnp, wake, flags);
> > +}
> 
> 
> Etc.. these are much harder to ignore than comments.

Good point!  I probably should do the same for interrupt disabling.

							Thanx, Paul

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