linux-kernel - Re: [PATCH rcu 4/6] rcu: Mark __rcu_irq_enter_check_tick() ->rcu_urgent

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Date:   Tue, 18 Jul 2023 08:58:45 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...a.com,
        rostedt@...dmis.org
Subject: Re: [PATCH rcu 4/6] rcu: Mark __rcu_irq_enter_check_tick()
 ->rcu_urgent_qs load

On 7/17/23 14:03, Paul E. McKenney wrote:
> The rcu_request_urgent_qs_task() function does a cross-CPU store
> to ->rcu_urgent_qs, so this commit therefore marks the load in
> __rcu_irq_enter_check_tick() with READ_ONCE().
> 
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---
>   kernel/rcu/tree.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index fae9b4e29c93..aec07f2ec638 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -632,7 +632,7 @@ void __rcu_irq_enter_check_tick(void)
>   	// prevents self-deadlock.  So we can safely recheck under the lock.
>   	// Note that the nohz_full state currently cannot change.
>   	raw_spin_lock_rcu_node(rdp->mynode);
> -	if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
> +	if (READ_ONCE(rdp->rcu_urgent_qs) && !rdp->rcu_forced_tick) {
>   		// A nohz_full CPU is in the kernel and RCU needs a
>   		// quiescent state.  Turn on the tick!
>   		WRITE_ONCE(rdp->rcu_forced_tick, 

Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>


thanks,

- Joel