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

[Lai Jiangshan <laijs@linux.alibaba.com>]

On 2019/10/15 10:00 上午, Paul E. McKenney wrote:
> On Tue, Oct 15, 2019 at 09:50:21AM +0800, Lai Jiangshan wrote:
>> On Tue, Oct 15, 2019 at 9:46 AM Paul E. McKenney <paulmck@kernel.org> wrote:
>>>
>>> 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.
>>
>> Oh, sorry
>>
>> I wrongly made the change base on upstream.
>> I will rebase later.
> 
> Very good, looking forward to this updated version.
> 
> 							Thanx, Paul


In my box, the patch can be applied to the -rcu "dev" well.
And there is nothing strange after boot.

Have I just made a mistake a again? In my box, the HEAD
of -rcu "dev" is 9725023b ("torture: Handle jitter for CPUs that cannot 
be offlined")

Thanks
Lai

> 
>> thanks
>> Lai
>>
>>>
>>>                                                          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
>>>>>