Re: [PATCH v2 4/6] sched_domain: Annotate RCU pointers properly

[Paul E. McKenney]

On Sat, Feb 23, 2019 at 01:34:32AM -0500, Joel Fernandes (Google) wrote:
> The scheduler uses RCU API in various places to access sched_domain
> pointers. These cause sparse errors as below.
> 
> Many new errors show up because of an annotation check I added to
> rcu_assign_pointer(). Let us annotate the pointers correctly which also
> will help sparse catch any potential future bugs.
> 
> This fixes the following sparse errors:
> 
> rt.c:1681:9: error: incompatible types in comparison expression
> deadline.c:1904:9: error: incompatible types in comparison expression
> core.c:519:9: error: incompatible types in comparison expression
> core.c:1634:17: error: incompatible types in comparison expression
> fair.c:6193:14: error: incompatible types in comparison expression
> fair.c:9883:22: error: incompatible types in comparison expression
> fair.c:9897:9: error: incompatible types in comparison expression
> sched.h:1287:9: error: incompatible types in comparison expression
> topology.c:612:9: error: incompatible types in comparison expression
> topology.c:615:9: error: incompatible types in comparison expression
> sched.h:1300:9: error: incompatible types in comparison expression
> topology.c:618:9: error: incompatible types in comparison expression
> sched.h:1287:9: error: incompatible types in comparison expression
> topology.c:621:9: error: incompatible types in comparison expression
> sched.h:1300:9: error: incompatible types in comparison expression
> topology.c:624:9: error: incompatible types in comparison expression
> topology.c:671:9: error: incompatible types in comparison expression
> stats.c:45:17: error: incompatible types in comparison expression
> fair.c:5998:15: error: incompatible types in comparison expression
> fair.c:5989:15: error: incompatible types in comparison expression
> fair.c:5998:15: error: incompatible types in comparison expression
> fair.c:5989:15: error: incompatible types in comparison expression
> fair.c:6120:19: error: incompatible types in comparison expression
> fair.c:6506:14: error: incompatible types in comparison expression
> fair.c:6515:14: error: incompatible types in comparison expression
> fair.c:6623:9: error: incompatible types in comparison expression
> fair.c:5970:17: error: incompatible types in comparison expression
> fair.c:8642:21: error: incompatible types in comparison expression
> fair.c:9253:9: error: incompatible types in comparison expression
> fair.c:9331:9: error: incompatible types in comparison expression
> fair.c:9519:15: error: incompatible types in comparison expression
> fair.c:9533:14: error: incompatible types in comparison expression
> fair.c:9542:14: error: incompatible types in comparison expression
> fair.c:9567:14: error: incompatible types in comparison expression
> fair.c:9597:14: error: incompatible types in comparison expression
> fair.c:9421:16: error: incompatible types in comparison expression
> fair.c:9421:16: error: incompatible types in comparison expression
> 
> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>

>From an RCU perspective:

Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>

> ---
>  include/linux/sched/topology.h |  4 ++--
>  kernel/sched/sched.h           | 14 +++++++-------
>  kernel/sched/topology.c        | 10 +++++-----
>  3 files changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
> index c31d3a47a47c..4819c9e01e42 100644
> --- a/include/linux/sched/topology.h
> +++ b/include/linux/sched/topology.h
> @@ -76,8 +76,8 @@ struct sched_domain_shared {
>  
>  struct sched_domain {
>  	/* These fields must be setup */
> -	struct sched_domain *parent;	/* top domain must be null terminated */
> -	struct sched_domain *child;	/* bottom domain must be null terminated */
> +	struct sched_domain __rcu *parent;	/* top domain must be null terminated */
> +	struct sched_domain __rcu *child;	/* bottom domain must be null terminated */
>  	struct sched_group *groups;	/* the balancing groups of the domain */
>  	unsigned long min_interval;	/* Minimum balance interval ms */
>  	unsigned long max_interval;	/* Maximum balance interval ms */
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 2ab545d40381..ca6a79f57e7a 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -866,8 +866,8 @@ struct rq {
>  	atomic_t		nr_iowait;
>  
>  #ifdef CONFIG_SMP
> -	struct root_domain	*rd;
> -	struct sched_domain	*sd;
> +	struct root_domain		*rd;
> +	struct sched_domain __rcu	*sd;
>  
>  	unsigned long		cpu_capacity;
>  	unsigned long		cpu_capacity_orig;
> @@ -1305,13 +1305,13 @@ static inline struct sched_domain *lowest_flag_domain(int cpu, int flag)
>  	return sd;
>  }
>  
> -DECLARE_PER_CPU(struct sched_domain *, sd_llc);
> +DECLARE_PER_CPU(struct sched_domain __rcu *, sd_llc);
>  DECLARE_PER_CPU(int, sd_llc_size);
>  DECLARE_PER_CPU(int, sd_llc_id);
> -DECLARE_PER_CPU(struct sched_domain_shared *, sd_llc_shared);
> -DECLARE_PER_CPU(struct sched_domain *, sd_numa);
> -DECLARE_PER_CPU(struct sched_domain *, sd_asym_packing);
> -DECLARE_PER_CPU(struct sched_domain *, sd_asym_cpucapacity);
> +DECLARE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared);
> +DECLARE_PER_CPU(struct sched_domain __rcu *, sd_numa);
> +DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
> +DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
>  extern struct static_key_false sched_asym_cpucapacity;
>  
>  struct sched_group_capacity {
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 3f35ba1d8fde..0844ee757dad 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -586,13 +586,13 @@ static void destroy_sched_domains(struct sched_domain *sd)
>   * the cpumask of the domain), this allows us to quickly tell if
>   * two CPUs are in the same cache domain, see cpus_share_cache().
>   */
> -DEFINE_PER_CPU(struct sched_domain *, sd_llc);
> +DEFINE_PER_CPU(struct sched_domain __rcu *, sd_llc);
>  DEFINE_PER_CPU(int, sd_llc_size);
>  DEFINE_PER_CPU(int, sd_llc_id);
> -DEFINE_PER_CPU(struct sched_domain_shared *, sd_llc_shared);
> -DEFINE_PER_CPU(struct sched_domain *, sd_numa);
> -DEFINE_PER_CPU(struct sched_domain *, sd_asym_packing);
> -DEFINE_PER_CPU(struct sched_domain *, sd_asym_cpucapacity);
> +DEFINE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared);
> +DEFINE_PER_CPU(struct sched_domain __rcu *, sd_numa);
> +DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
> +DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
>  DEFINE_STATIC_KEY_FALSE(sched_asym_cpucapacity);
>  
>  static void update_top_cache_domain(int cpu)
> -- 
> 2.21.0.rc0.258.g878e2cd30e-goog
>