Re: [PATCH 2/2] context_tracking: Invoke Tasks-RCU enter/exit for NMI context

[Frederic Weisbecker <frederic@kernel.org>]

Le Wed, Aug 07, 2024 at 10:05:06PM +0530, neeraj.upadhyay@kernel.org a écrit :
> From: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
> 
> rcu_task_enter() and rcu_task_exit() are not called on NMI
> entry and exit. So, Tasks-RCU-Rude grace period wait is required to
> ensure that NMI handlers have entered/exited into Tasks-RCU eqs.
> For architectures which do not require Tasks-RCU-Rude (as the code
> sections where RCU is not watching are marked as noinstr), when
> those architectures switch to not using Tasks-RCU-Rude, NMI handlers
> task exit to eqs will need to be handled correctly for Tasks-RCU holdout
> tasks running on nohz_full CPUs. As it is safe to call these two
> functions from NMI context, remove the in_nmi() check to ensure that
> Tasks-RCU entry/exit is marked correctly for NMI handlers.
> 
> Reported-by: Frederic Weisbecker <frederic@kernel.org>
> Suggested-by: Frederic Weisbecker <frederic@kernel.org>
> Suggested-by: "Paul E. McKenney" <paulmck@kernel.org>
> Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
> ---
>  kernel/context_tracking.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> index 152b485a62db..626dd7a173a5 100644
> --- a/kernel/context_tracking.c
> +++ b/kernel/context_tracking.c
> @@ -239,8 +239,7 @@ void noinstr ct_nmi_exit(void)
>  	ct_kernel_exit_state(CT_RCU_WATCHING);
>  	// ... but is no longer watching here.
>  
> -	if (!in_nmi())
> -		rcu_task_exit();
> +	rcu_task_exit();

And now since it is called by all callers of ct_kernel_exit_state(), you
can call it from it directly.

>  }
>  
>  /**
> @@ -273,8 +272,7 @@ void noinstr ct_nmi_enter(void)
>  	 */
>  	if (!rcu_is_watching_curr_cpu()) {
>  
> -		if (!in_nmi())
> -			rcu_task_enter();
> +		rcu_task_enter();
>  
>  		// RCU is not watching here ...
>  		ct_kernel_enter_state(CT_RCU_WATCHING);

Ditto for ct_kernel_enter_state().

Thanks.

> -- 
> 2.40.1
>