linux-kernel - Re: [PATCH] rcu/exp: Fix check for idle context in rcu_exp

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Date:   Mon, 13 Dec 2021 12:34:55 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Neeraj Upadhyay <quic_neeraju@...cinc.com>
Cc:     paulmck@...nel.org, josh@...htriplett.org, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        joel@...lfernandes.org, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org, urezki@...il.com,
        boqun.feng@...il.com
Subject: Re: [PATCH] rcu/exp: Fix check for idle context in rcu_exp_handler

On Mon, Dec 13, 2021 at 11:40:24AM +0530, Neeraj Upadhyay wrote:
> For PREEMPT_RCU, the rcu_exp_handler() function checks
> whether the current CPU is in idle, by calling
> rcu_dynticks_curr_cpu_in_eqs(). However, rcu_exp_handler()
> is called in IPI handler context. So, it should be checking
> the idle context using rcu_is_cpu_rrupt_from_idle(). Fix this
> by using rcu_is_cpu_rrupt_from_idle() instead of
> rcu_dynticks_curr_cpu_in_eqs(). Non-preempt configuration
> already uses the correct check.
> 
> Signed-off-by: Neeraj Upadhyay <quic_neeraju@...cinc.com>

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>


> ---
>  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 237a79989aba..1568c8ef185b 100644
> --- a/kernel/rcu/tree_exp.h
> +++ b/kernel/rcu/tree_exp.h
> @@ -656,7 +656,7 @@ static void rcu_exp_handler(void *unused)
>  	 */
>  	if (!depth) {
>  		if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) ||
> -		    rcu_dynticks_curr_cpu_in_eqs()) {
> +		    rcu_is_cpu_rrupt_from_idle()) {
>  			rcu_report_exp_rdp(rdp);
>  		} else {
>  			WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
> -- 
> 2.17.1
>