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Subject: Re: [PATCH] rcu: make PREEMPT_RCU to be a decoration of TREE_RCU
From:   Lai Jiangshan <laijs@linux.alibaba.com>
To:     paulmck@kernel.org, Lai Jiangshan <jiangshanlai@gmail.com>
Cc:     Joel Fernandes <joel@joelfernandes.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Ingo Molnar <mingo@redhat.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        David Sterba <dsterba@suse.com>,
        Yafang Shao <laoar.shao@gmail.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Petr Mladek <pmladek@suse.com>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        rcu@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>
References: <20191013125959.3280-1-laijs@linux.alibaba.com>
 <20191014184832.GA125935@google.com>
 <20191015014650.GL2689@paulmck-ThinkPad-P72>
 <CAJhGHyCMa7mU_K+-22MHGwJ+BfFun=2ndzehZCMoNrgYfBowaQ@mail.gmail.com>
 <20191015020023.GO2689@paulmck-ThinkPad-P72>
 <6bc1c7ef-5389-3a88-9ffe-c8c56e22a11a@linux.alibaba.com>
Message-ID: <ad88e699-5eba-e425-77ae-a73bcf4492e0@linux.alibaba.com>
Date:   Tue, 15 Oct 2019 11:01:00 +0800
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On 2019/10/15 10:45 上午, Lai Jiangshan wrote:
> 
> 
> 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.

Oh, I first applied it by "git cherry-pick" not "git am".
It did have conflicts when using "git am". Updated patch
was sent, sorry for the nosing.

thanks
Lai


> 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
>>>>>>