Re: [PATCH 3/5] Add rcu_barrier_sched() and rcu_barrier_bh()

[Gautham R Shenoy <ego@in.ibm.com>]

On Mon, May 05, 2008 at 07:47:51AM -0700, Paul E. McKenney wrote:
> On Mon, May 05, 2008 at 02:52:40PM +0530, Gautham R Shenoy wrote:
> > On Mon, Apr 21, 2008 at 05:47:43PM -0700, Paul E. McKenney wrote:
> > > Add rcu_barrier_sched() and rcu_barrier_bh().  With these in place,
> > > rcutorture no longer gives the occasional oops when repeatedly starting
> > > and stopping torturing rcu_bh.  Also adds the API needed to flush out
> > > pre-existing call_rcu_sched() callbacks.
> 
> Thank you again for looking it over!
> 
> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
> > > ---
> > > 
> > >  include/linux/rcupdate.h |    2 +
> > >  kernel/rcupdate.c        |   55 +++++++++++++++++++++++++++++++++++++++++------
> > >  2 files changed, 51 insertions(+), 6 deletions(-)
> > > 
> > > diff -urpNa -X dontdiff linux-2.6.25-C2-rcuclassic-fixes/include/linux/rcupdate.h linux-2.6.25-C3-rcu_barrier_sched/include/linux/rcupdate.h
> > > --- linux-2.6.25-C2-rcuclassic-fixes/include/linux/rcupdate.h	2008-04-17 08:10:33.000000000 -0700
> > > +++ linux-2.6.25-C3-rcu_barrier_sched/include/linux/rcupdate.h	2008-04-21 11:33:07.000000000 -0700
> > > @@ -260,6 +260,8 @@ extern void call_rcu_bh(struct rcu_head 
> > >  /* Exported common interfaces */
> > >  extern void synchronize_rcu(void);
> > >  extern void rcu_barrier(void);
> > > +extern void rcu_barrier_bh(void);
> > > +extern void rcu_barrier_sched(void);
> > >  extern long rcu_batches_completed(void);
> > >  extern long rcu_batches_completed_bh(void);
> > > 
> > > diff -urpNa -X dontdiff linux-2.6.25-C2-rcuclassic-fixes/kernel/rcupdate.c linux-2.6.25-C3-rcu_barrier_sched/kernel/rcupdate.c
> > > --- linux-2.6.25-C2-rcuclassic-fixes/kernel/rcupdate.c	2008-04-17 08:10:33.000000000 -0700
> > > +++ linux-2.6.25-C3-rcu_barrier_sched/kernel/rcupdate.c	2008-04-21 11:33:08.000000000 -0700
> > > @@ -45,6 +45,12 @@
> > >  #include <linux/mutex.h>
> > >  #include <linux/module.h>
> > > 
> > > +enum rcu_barrier {
> > > +	RCU_BARRIER_STD,
> > STD: Standard, I take it ?
> 
> Yep.  Could say just "RCU_BARRIER", or perhaps "RCU_BARRIER_CLASSIC".
> Or comment each with the primitive they go with, perhaps better.

A simple RCU_BARRIER should do I guess, since the corresponding
API is rcu_barrier(). With comments, that'll be even better :-)

-- 
Thanks and Regards
gautham.

> 
> > > +	RCU_BARRIER_BH,
> > > +	RCU_BARRIER_SCHED,
> > > +};
> > > +
> > >  static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
> > >  static atomic_t rcu_barrier_cpu_count;
> > >  static DEFINE_MUTEX(rcu_barrier_mutex);
> > > @@ -83,19 +89,30 @@ static void rcu_barrier_callback(struct 
> > >  /*
> > >   * Called with preemption disabled, and from cross-cpu IRQ context.
> > >   */
> > > -static void rcu_barrier_func(void *notused)
> > > +static void rcu_barrier_func(void *type)
> > >  {
> > >  	int cpu = smp_processor_id();
> > >  	struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
> > > 
> > >  	atomic_inc(&rcu_barrier_cpu_count);
> > > -	call_rcu(head, rcu_barrier_callback);
> > > +	switch ((enum rcu_barrier)type) {
> > > +	case RCU_BARRIER_STD:
> > > +		call_rcu(head, rcu_barrier_callback);
> > > +		break;
> > > +	case RCU_BARRIER_BH:
> > > +		call_rcu_bh(head, rcu_barrier_callback);
> > > +		break;
> > > +	case RCU_BARRIER_SCHED:
> > > +		call_rcu_sched(head, rcu_barrier_callback);
> > > +		break;
> > > +	}
> > >  }
> > > 
> > > -/**
> > > - * rcu_barrier - Wait until all the in-flight RCUs are complete.
> > > +/*
> > > + * Orchestrate the specified type of RCU barrier, waiting for all
> > > + * RCU callbacks of the specified type to complete.
> > >   */
> > > -void rcu_barrier(void)
> > > +static void _rcu_barrier(enum rcu_barrier type)
> > >  {
> > >  	BUG_ON(in_interrupt());
> > >  	/* Take cpucontrol mutex to protect against CPU hotplug */
> > > @@ -111,13 +128,39 @@ void rcu_barrier(void)
> > >  	 * until all the callbacks are queued.
> > >  	 */
> > >  	rcu_read_lock();
> > > -	on_each_cpu(rcu_barrier_func, NULL, 0, 1);
> > > +	on_each_cpu(rcu_barrier_func, (void *)type, 0, 1);
> > >  	rcu_read_unlock();
> > >  	wait_for_completion(&rcu_barrier_completion);
> > >  	mutex_unlock(&rcu_barrier_mutex);
> > >  }
> > > +
> > > +/**
> > > + * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
> > > + */
> > > +void rcu_barrier(void)
> > > +{
> > > +	_rcu_barrier(RCU_BARRIER_STD);
> > > +}
> > >  EXPORT_SYMBOL_GPL(rcu_barrier);
> > > 
> > > +/**
> > > + * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
> > > + */
> > > +void rcu_barrier_bh(void)
> > > +{
> > > +	_rcu_barrier(RCU_BARRIER_BH);
> > > +}
> > > +EXPORT_SYMBOL_GPL(rcu_barrier_bh);
> > > +
> > > +/**
> > > + * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
> > > + */
> > > +void rcu_barrier_sched(void)
> > > +{
> > > +	_rcu_barrier(RCU_BARRIER_SCHED);
> > > +}
> > > +EXPORT_SYMBOL_GPL(rcu_barrier_sched);
> > > +
> > >  void __init rcu_init(void)
> > >  {
> > >  	__rcu_init();
> > 
> > -- 
> > Thanks and Regards
> > gautham