Re: [PATCH 2/4] rcu: Remove useless WRITE_ONCE() on rcu_data.exp_deferred_qs

[Paul E. McKenney]

On Thu, Sep 16, 2021 at 02:10:46PM +0200, Frederic Weisbecker wrote:
> This variable is never written nor read remotely. Remove this confusion.
> 
> Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
> ---
>  kernel/rcu/tree_exp.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
> index f3947c49eee7..4266610b4587 100644
> --- a/kernel/rcu/tree_exp.h
> +++ b/kernel/rcu/tree_exp.h
> @@ -255,7 +255,7 @@ static void rcu_report_exp_cpu_mult(struct rcu_node *rnp,
>   */
>  static void rcu_report_exp_rdp(struct rcu_data *rdp)
>  {
> -	WRITE_ONCE(rdp->exp_deferred_qs, false);
> +	rdp->exp_deferred_qs = false;

Are you sure that this can never be invoked from an interrupt handler?
And that rdp->exp_deferred_qs is never read from an interrupt handler?
If either can happen, then the WRITE_ONCE() does play a role, right?

							Thanx, Paul

>  	rcu_report_exp_cpu_mult(rdp->mynode, rdp->grpmask, true);
>  }
>  
> -- 
> 2.25.1
>