Subject: Re: [PATCH v2 3/6] sched/cpufreq: Annotate cpufreq_update_util_data pointer with __rcu

From: Joel Fernandes <[email-masked]>
Date: Wed, 27 Feb 2019 10:42:16 -0500

On Mon, Feb 25, 2019 at 01:10:26PM -0800, Paul E. McKenney wrote:
> On Sat, Feb 23, 2019 at 01:34:31AM -0500, Joel Fernandes (Google) wrote:
> > Recently I added an RCU annotation check to rcu_assign_pointer(). All
> > pointers assigned to RCU protected data are to be annotated with __rcu
> > inorder to be able to use rcu_assign_pointer() similar to checks in
> > other RCU APIs.
> > 
> > This resulted in a sparse error: kernel//sched/cpufreq.c:41:9: sparse:
> > error: incompatible types in comparison expression (different address
> > spaces)
> > 
> > Fix this by annotating cpufreq_update_util_data pointer with __rcu. This
> > will also help sparse catch any future RCU misuage bugs.
> > 
> > Signed-off-by: Joel Fernandes (Google) <[email-masked]>
> 
> From an RCU perspective:
> 
> Reviewed-by: Paul E. McKenney <[email-masked]>

Thanks a lot Paul.

Peter, Rafael, Steve,
Are you Ok with the patches 3-6? It will be nice to quiet down sparse.

thanks,

 - Joel

> > ---
> >  kernel/sched/cpufreq.c | 2 +-
> >  kernel/sched/sched.h   | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/sched/cpufreq.c b/kernel/sched/cpufreq.c
> > index 22bd8980f32f..e316ee7bb2e5 100644
> > --- a/kernel/sched/cpufreq.c
> > +++ b/kernel/sched/cpufreq.c
> > @@ -7,7 +7,7 @@
> >   */
> >  #include "sched.h"
> >  
> > -DEFINE_PER_CPU(struct update_util_data *, cpufreq_update_util_data);
> > +DEFINE_PER_CPU(struct update_util_data __rcu *, cpufreq_update_util_data);
> >  
> >  /**
> >   * cpufreq_add_update_util_hook - Populate the CPU's update_util_data pointer.
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index d04530bf251f..2ab545d40381 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -2166,7 +2166,7 @@ static inline u64 irq_time_read(int cpu)
> >  #endif /* CONFIG_IRQ_TIME_ACCOUNTING */
> >  
> >  #ifdef CONFIG_CPU_FREQ
> > -DECLARE_PER_CPU(struct update_util_data *, cpufreq_update_util_data);
> > +DECLARE_PER_CPU(struct update_util_data __rcu *, cpufreq_update_util_data);
> >  
> >  /**
> >   * cpufreq_update_util - Take a note about CPU utilization changes.
> > -- 
> > 2.21.0.rc0.258.g878e2cd30e-goog
> > 
>