[PATCH] rcu-tasks: Remove unnecessary smp_store operations in the cblist_init_generic()

[PATCH] rcu-tasks: Remove unnecessary smp_store operations in the cblist_init_generic()

[Zqiang]

The cblist_init_generic() is executed during the CPU early boot
phase due to commit:30ef09635b9e ("rcu-tasks: Initialize callback
lists at rcu_init() time"), at this time, only one boot CPU is
online. this commit therefore use WRITE_ONCE() to replace the
smp_store_release() to assigning rtp->percpu_enqueue_lim in the
cblist_init_generic().

Signed-off-by: Zqiang <qiang.zhang@linux.dev>
---
 kernel/rcu/tasks.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 76f952196a29..f763f60d5e50 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -292,7 +292,7 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
 		shift++;
 	WRITE_ONCE(rtp->percpu_enqueue_shift, shift);
 	WRITE_ONCE(rtp->percpu_dequeue_lim, lim);
-	smp_store_release(&rtp->percpu_enqueue_lim, lim);
+	WRITE_ONCE(rtp->percpu_enqueue_lim, lim);
 
 	pr_info("%s: Setting shift to %d and lim to %d rcu_task_cb_adjust=%d rcu_task_cpu_ids=%d.\n",
 			rtp->name, data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim),
-- 
2.48.1

Re: [PATCH] rcu-tasks: Remove unnecessary smp_store operations in the cblist_init_generic()

[Paul E. McKenney]

On Sun, Dec 14, 2025 at 10:49:04AM +0800, Zqiang wrote:
> The cblist_init_generic() is executed during the CPU early boot
> phase due to commit:30ef09635b9e ("rcu-tasks: Initialize callback
> lists at rcu_init() time"), at this time, only one boot CPU is
> online. this commit therefore use WRITE_ONCE() to replace the
> smp_store_release() to assigning rtp->percpu_enqueue_lim in the
> cblist_init_generic().
> 
> Signed-off-by: Zqiang <qiang.zhang@linux.dev>

Good eyes, thank you!

But in that case, we are running on a single CPU with interrupts disables,
so do we even need WRITE_ONCE()?

							Thanx, Paul

> ---
>  kernel/rcu/tasks.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index 76f952196a29..f763f60d5e50 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -292,7 +292,7 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
>  		shift++;
>  	WRITE_ONCE(rtp->percpu_enqueue_shift, shift);
>  	WRITE_ONCE(rtp->percpu_dequeue_lim, lim);
> -	smp_store_release(&rtp->percpu_enqueue_lim, lim);
> +	WRITE_ONCE(rtp->percpu_enqueue_lim, lim);
>  
>  	pr_info("%s: Setting shift to %d and lim to %d rcu_task_cb_adjust=%d rcu_task_cpu_ids=%d.\n",
>  			rtp->name, data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim),
> -- 
> 2.48.1
> 

Re: [PATCH] rcu-tasks: Remove unnecessary smp_store operations in the cblist_init_generic()

[Zqiang]

> 
> On Sun, Dec 14, 2025 at 10:49:04AM +0800, Zqiang wrote:
> 
> > 
> > The cblist_init_generic() is executed during the CPU early boot
> >  phase due to commit:30ef09635b9e ("rcu-tasks: Initialize callback
> >  lists at rcu_init() time"), at this time, only one boot CPU is
> >  online. this commit therefore use WRITE_ONCE() to replace the
> >  smp_store_release() to assigning rtp->percpu_enqueue_lim in the
> >  cblist_init_generic().
> >  
> >  Signed-off-by: Zqiang <qiang.zhang@linux.dev>
> > 
> Good eyes, thank you!
> 
> But in that case, we are running on a single CPU with interrupts disables,
> so do we even need WRITE_ONCE()?

I missed the interrupts disabled, It seems like there are no need use WRITE_ONCE()
and include above, I will update and resend.

Thanks
Zqiang




> 
>  Thanx, Paul
> 
> > 
> > ---
> >  kernel/rcu/tasks.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >  
> >  diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> >  index 76f952196a29..f763f60d5e50 100644
> >  --- a/kernel/rcu/tasks.h
> >  +++ b/kernel/rcu/tasks.h
> >  @@ -292,7 +292,7 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
> >  shift++;
> >  WRITE_ONCE(rtp->percpu_enqueue_shift, shift);
> >  WRITE_ONCE(rtp->percpu_dequeue_lim, lim);
> >  - smp_store_release(&rtp->percpu_enqueue_lim, lim);
> >  + WRITE_ONCE(rtp->percpu_enqueue_lim, lim);
> >  
> >  pr_info("%s: Setting shift to %d and lim to %d rcu_task_cb_adjust=%d rcu_task_cpu_ids=%d.\n",
> >  rtp->name, data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim),
> >  -- 
> >  2.48.1
> >
>