Re: [PATCH] rcu: make PREEMPT_RCU to be a decoration of TREE_RCU

[Joel Fernandes]

On Sun, Oct 13, 2019 at 12:59:57PM +0000, Lai Jiangshan wrote:
> Currently PREEMPT_RCU and TREE_RCU are "contrary" configs
> when they can't be both on. But PREEMPT_RCU is actually a kind
> of TREE_RCU in the implementation. It seams to be appropriate
> to make PREEMPT_RCU to be a decorative option of TREE_RCU.
> 

Looks like a nice simplification and so far I could not poke any holes in the
code...

I am in support of this patch for further review and testing. Thanks!

Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>

thanks,

 - Joel


> Signed-off-by: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
> Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
> ---
>  include/linux/rcupdate.h   |  4 ++--
>  include/trace/events/rcu.h |  4 ++--
>  kernel/rcu/Kconfig         | 13 +++++++------
>  kernel/rcu/Makefile        |  1 -
>  kernel/rcu/rcu.h           |  2 +-
>  kernel/rcu/update.c        |  2 +-
>  kernel/sysctl.c            |  2 +-
>  7 files changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 75a2eded7aa2..1eee9f6c27f9 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -167,7 +167,7 @@ do { \
>   * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
>   */
>  
> -#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
> +#if defined(CONFIG_TREE_RCU)
>  #include <linux/rcutree.h>
>  #elif defined(CONFIG_TINY_RCU)
>  #include <linux/rcutiny.h>
> @@ -583,7 +583,7 @@ do {									      \
>   * read-side critical section that would block in a !PREEMPT kernel.
>   * But if you want the full story, read on!
>   *
> - * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),
> + * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU),
>   * it is illegal to block while in an RCU read-side critical section.
>   * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION
>   * kernel builds, RCU read-side critical sections may be preempted,
> diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
> index 694bd040cf51..1ce15c5be4c8 100644
> --- a/include/trace/events/rcu.h
> +++ b/include/trace/events/rcu.h
> @@ -41,7 +41,7 @@ TRACE_EVENT(rcu_utilization,
>  	TP_printk("%s", __entry->s)
>  );
>  
> -#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
> +#if defined(CONFIG_TREE_RCU)
>  
>  /*
>   * Tracepoint for grace-period events.  Takes a string identifying the
> @@ -425,7 +425,7 @@ TRACE_EVENT_RCU(rcu_fqs,
>  		  __entry->cpu, __entry->qsevent)
>  );
>  
> -#endif /* #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU) */
> +#endif /* #if defined(CONFIG_TREE_RCU) */
>  
>  /*
>   * Tracepoint for dyntick-idle entry/exit events.  These take a string
> diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
> index 7644eda17d62..0303934e6ef0 100644
> --- a/kernel/rcu/Kconfig
> +++ b/kernel/rcu/Kconfig
> @@ -7,7 +7,7 @@ menu "RCU Subsystem"
>  
>  config TREE_RCU
>  	bool
> -	default y if !PREEMPTION && SMP
> +	default y if SMP
>  	help
>  	  This option selects the RCU implementation that is
>  	  designed for very large SMP system with hundreds or
> @@ -17,6 +17,7 @@ config TREE_RCU
>  config PREEMPT_RCU
>  	bool
>  	default y if PREEMPTION
> +	select TREE_RCU
>  	help
>  	  This option selects the RCU implementation that is
>  	  designed for very large SMP systems with hundreds or
> @@ -78,7 +79,7 @@ config TASKS_RCU
>  	  user-mode execution as quiescent states.
>  
>  config RCU_STALL_COMMON
> -	def_bool ( TREE_RCU || PREEMPT_RCU )
> +	def_bool TREE_RCU
>  	help
>  	  This option enables RCU CPU stall code that is common between
>  	  the TINY and TREE variants of RCU.  The purpose is to allow
> @@ -86,13 +87,13 @@ config RCU_STALL_COMMON
>  	  making these warnings mandatory for the tree variants.
>  
>  config RCU_NEED_SEGCBLIST
> -	def_bool ( TREE_RCU || PREEMPT_RCU || TREE_SRCU )
> +	def_bool ( TREE_RCU || TREE_SRCU )
>  
>  config RCU_FANOUT
>  	int "Tree-based hierarchical RCU fanout value"
>  	range 2 64 if 64BIT
>  	range 2 32 if !64BIT
> -	depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
> +	depends on TREE_RCU && RCU_EXPERT
>  	default 64 if 64BIT
>  	default 32 if !64BIT
>  	help
> @@ -112,7 +113,7 @@ config RCU_FANOUT_LEAF
>  	int "Tree-based hierarchical RCU leaf-level fanout value"
>  	range 2 64 if 64BIT
>  	range 2 32 if !64BIT
> -	depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
> +	depends on TREE_RCU && RCU_EXPERT
>  	default 16
>  	help
>  	  This option controls the leaf-level fanout of hierarchical
> @@ -187,7 +188,7 @@ config RCU_BOOST_DELAY
>  
>  config RCU_NOCB_CPU
>  	bool "Offload RCU callback processing from boot-selected CPUs"
> -	depends on TREE_RCU || PREEMPT_RCU
> +	depends on TREE_RCU
>  	depends on RCU_EXPERT || NO_HZ_FULL
>  	default n
>  	help
> diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile
> index 020e8b6a644b..82d5fba48b2f 100644
> --- a/kernel/rcu/Makefile
> +++ b/kernel/rcu/Makefile
> @@ -9,6 +9,5 @@ obj-$(CONFIG_TINY_SRCU) += srcutiny.o
>  obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
>  obj-$(CONFIG_RCU_PERF_TEST) += rcuperf.o
>  obj-$(CONFIG_TREE_RCU) += tree.o
> -obj-$(CONFIG_PREEMPT_RCU) += tree.o
>  obj-$(CONFIG_TINY_RCU) += tiny.o
>  obj-$(CONFIG_RCU_NEED_SEGCBLIST) += rcu_segcblist.o
> diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
> index 8fd4f82c9b3d..4149ba76824f 100644
> --- a/kernel/rcu/rcu.h
> +++ b/kernel/rcu/rcu.h
> @@ -452,7 +452,7 @@ enum rcutorture_type {
>  	INVALID_RCU_FLAVOR
>  };
>  
> -#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
> +#if defined(CONFIG_TREE_RCU)
>  void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
>  			    unsigned long *gp_seq);
>  void rcutorture_record_progress(unsigned long vernum);
> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> index 1861103662db..34a7452b25fd 100644
> --- a/kernel/rcu/update.c
> +++ b/kernel/rcu/update.c
> @@ -435,7 +435,7 @@ struct debug_obj_descr rcuhead_debug_descr = {
>  EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
>  #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
>  
> -#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
> +#if defined(CONFIG_TREE_RCU) || defined(CONFIG_RCU_TRACE)
>  void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp,
>  			       unsigned long secs,
>  			       unsigned long c_old, unsigned long c)
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 00fcea236eba..2ace158a4d72 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1268,7 +1268,7 @@ static struct ctl_table kern_table[] = {
>  		.proc_handler	= proc_do_static_key,
>  	},
>  #endif
> -#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
> +#if defined(CONFIG_TREE_RCU)
>  	{
>  		.procname	= "panic_on_rcu_stall",
>  		.data		= &sysctl_panic_on_rcu_stall,
> -- 
> 2.20.1
>