linux-kernel - Re: [PATCH rcu 04/12] rcu: Immediately boost preempted readers for strict grace periods

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Message-ID: <789b9966-f899-3882-768d-e996e43ec6da@quicinc.com>
Date:   Tue, 21 Jun 2022 11:30:39 +0530
From:   Neeraj Upadhyay <quic_neeraju@...cinc.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>, <rcu@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <kernel-team@...com>,
        <rostedt@...dmis.org>, Zqiang <qiang1.zhang@...el.com>
Subject: Re: [PATCH rcu 04/12] rcu: Immediately boost preempted readers for
 strict grace periods



On 6/21/2022 3:50 AM, Paul E. McKenney wrote:
> From: Zqiang <qiang1.zhang@...el.com>
> 
> The intent of the CONFIG_RCU_STRICT_GRACE_PERIOD Konfig option is to
> cause normal grace periods to complete quickly in order to better catch
> errors resulting from improperly leaking pointers from RCU read-side
> critical sections.  However, kernels built with this option enabled still
> wait for some hundreds of milliseconds before boosting RCU readers that
> have been preempted within their current critical section.  The value
> of this delay is set by the CONFIG_RCU_BOOST_DELAY Kconfig option,
> which defaults to 500 milliseconds.
> 
> This commit therefore causes kernels build with strict grace periods
> to ignore CONFIG_RCU_BOOST_DELAY.  This causes rcu_initiate_boost()
> to start boosting immediately after all CPUs on a given leaf rcu_node
> structure have passed through their quiescent states.
> 
> Signed-off-by: Zqiang <qiang1.zhang@...el.com>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---

Reviewed-by: Neeraj Upadhyay <quic_neeraju@...cinc.com>


Thanks
Neeraj

>   kernel/rcu/tree_plugin.h | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 440d9e02a26e0..53d05eb804121 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -1140,7 +1140,8 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
>   	    (rnp->gp_tasks != NULL &&
>   	     rnp->boost_tasks == NULL &&
>   	     rnp->qsmask == 0 &&
> -	     (!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld))) {
> +	     (!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld ||
> +	      IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)))) {
>   		if (rnp->exp_tasks == NULL)
>   			WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks);
>   		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);