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

["Paul E. McKenney" <paulmck@kernel.org>]

On Mon, Oct 14, 2019 at 02:48:32PM -0400, Joel Fernandes wrote:
> 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@joelfernandes.org>

Thank you both!

Lai, what is this patch against?  It does not want to apply to the current
-rcu "dev" branch.

							Thanx, Paul

> thanks,
> 
>  - Joel
> 
> 
> > Signed-off-by: Lai Jiangshan <jiangshanlai@gmail.com>
> > Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
> > ---
> >  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
> >