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[04/12] rcu: Immediately boost preempted readers for strict grace periods

Message ID 20220620222032.3839547-4-paulmck@kernel.org (mailing list archive)
State Accepted
Commit cf07fec8ee4f3949d6a9a43055a6ef3b4f094026
Headers show
Series Miscellaneous fixes for v5.20 | expand

Commit Message

Paul E. McKenney June 20, 2022, 10:20 p.m. UTC 
From: Zqiang <qiang1.zhang@intel.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@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree_plugin.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Neeraj Upadhyay June 21, 2022, 6 a.m. UTC | #1 
On 6/21/2022 3:50 AM, Paul E. McKenney wrote:
> From: Zqiang <qiang1.zhang@intel.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@intel.com>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> ---

Reviewed-by: Neeraj Upadhyay <quic_neeraju@quicinc.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);
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Patch

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);