linux-kernel - Re: [PATCH v2 13/27] context_tracking, rcu: Rename rcu_dynticks_task*() into rcu

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Date: Mon, 13 May 2024 20:39:31 +0200
From: Valentin Schneider <vschneid@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: rcu@...r.kernel.org, linux-kernel@...r.kernel.org, "Paul E. McKenney"
 <paulmck@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Neeraj
 Upadhyay <quic_neeraju@...cinc.com>, Joel Fernandes
 <joel@...lfernandes.org>, Josh Triplett <josh@...htriplett.org>, Boqun
 Feng <boqun.feng@...il.com>, Steven Rostedt <rostedt@...dmis.org>, Mathieu
 Desnoyers <mathieu.desnoyers@...icios.com>, Lai Jiangshan
 <jiangshanlai@...il.com>, Zqiang <qiang.zhang1211@...il.com>
Subject: Re: [PATCH v2 13/27] context_tracking, rcu: Rename
 rcu_dynticks_task*() into rcu_task*()

On 08/05/24 16:39, Frederic Weisbecker wrote:
> Le Tue, Apr 30, 2024 at 11:17:17AM +0200, Valentin Schneider a écrit :
>> The context_tracking.state RCU_DYNTICKS subvariable has been renamed to
>> RCU_WATCHING, and the 'dynticks' prefix can be dropped without losing any
>> meaning.
>>
>> Suggested-by: Frederic Weisbecker <frederic@...nel.org>
>> Signed-off-by: Valentin Schneider <vschneid@...hat.com>
>> ---
>>  kernel/context_tracking.c | 20 ++++++++++----------
>>  1 file changed, 10 insertions(+), 10 deletions(-)
>>
>> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
>> index 647939b0befd9..9c8f7b9191cd4 100644
>> --- a/kernel/context_tracking.c
>> +++ b/kernel/context_tracking.c
>> @@ -39,7 +39,7 @@ EXPORT_SYMBOL_GPL(context_tracking);
>>  #define TPS(x)  tracepoint_string(x)
>>
>>  /* Record the current task on dyntick-idle entry. */
>> -static __always_inline void rcu_dynticks_task_enter(void)
>> +static __always_inline void rcu_task_enter(void)
>
> On a second thought, this should be the reverse. We are not
> telling anymore that we are entering dynticks mode from an
> RCU-task perspective. We are telling that we are exiting RCU-tasks
> because we are in eqs mode (even though this is mostly a concern
> for nohz_full here, as idle tasks are entirely quiescent states
> but anyway...).
>
> So this should be s/rcu_dynticks_task_enter/rcu_task_exit
>

That definitely makes more sense, thanks!

>>  {
>>  #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
>>      WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
>> @@ -47,7 +47,7 @@ static __always_inline void rcu_dynticks_task_enter(void)
>>  }
>>
>>  /* Record no current task on dyntick-idle exit. */
>> -static __always_inline void rcu_dynticks_task_exit(void)
>> +static __always_inline void rcu_task_exit(void)
>
> And s/rcu_dynticks_task_exit/rcu_task_enter
>
>>  {
>>  #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
>>      WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
>> @@ -55,7 +55,7 @@ static __always_inline void rcu_dynticks_task_exit(void)
>>  }
>>
>>  /* Turn on heavyweight RCU tasks trace readers on idle/user entry. */
>> -static __always_inline void rcu_dynticks_task_trace_enter(void)
>> +static __always_inline void rcu_task_trace_enter(void)
>
> The same reverse naming goes for task_trace (even though I can't make
> sense right now of what the barrier it implies orders exactly, but that's
> another story)

Ack.

>
>>  {
>>  #ifdef CONFIG_TASKS_TRACE_RCU
>>      if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
>> @@ -64,7 +64,7 @@ static __always_inline void rcu_dynticks_task_trace_enter(void)
>>  }
>>
>>  /* Turn off heavyweight RCU tasks trace readers on idle/user exit. */
>> -static __always_inline void rcu_dynticks_task_trace_exit(void)
>> +static __always_inline void rcu_task_trace_exit(void)
>>  {
>>  #ifdef CONFIG_TASKS_TRACE_RCU
>>      if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
>> @@ -87,7 +87,7 @@ static noinstr void ct_kernel_exit_state(int offset)
>>       * critical sections, and we also must force ordering with the
>>       * next idle sojourn.
>>       */
>> -	rcu_dynticks_task_trace_enter();  // Before ->dynticks update!
>> +	rcu_task_trace_enter();  // Before ->dynticks update!
>
> s/->dynticks/->state
>
>>      seq = ct_state_inc(offset);
>>      // RCU is no longer watching.  Better be in extended quiescent state!
>>      WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (seq & CT_RCU_WATCHING));
>> @@ -109,7 +109,7 @@ static noinstr void ct_kernel_enter_state(int offset)
>>       */
>>      seq = ct_state_inc(offset);
>>      // RCU is now watching.  Better not be in an extended quiescent state!
>> -	rcu_dynticks_task_trace_exit();  // After ->dynticks update!
>> +	rcu_task_trace_exit();  // After ->dynticks update!
>
> ditto

I've got these fixed in 25/27, but I can fold it down into the patches that
touch the related areas.

>
> Thanks!