linux-kernel - RE: [PATCH] rcu: Check the validity of the boost_kthread

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Date:   Fri, 25 Mar 2022 00:00:47 +0000
From:   "Zhang, Qiang1" <qiang1.zhang@...el.com>
To:     "paulmck@...nel.org" <paulmck@...nel.org>
CC:     "frederic@...nel.org" <frederic@...nel.org>,
        "quic_neeraju@...cinc.com" <quic_neeraju@...cinc.com>,
        "rcu@...r.kernel.org" <rcu@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] rcu: Check the validity of the boost_kthread_task pointer

On Thu, Mar 24, 2022 at 07:15:15PM +0800, Zqiang wrote:
> The boost kthreads may spawn failed, although the probability of 
> creation failure is very low, in consideration of the robustness of 
> the code, add boost_kthread_task pointer detection.
> 
> Signed-off-by: Zqiang <qiang1.zhang@...el.com>
>
>Good catch!  As you say, rare, but definitely worth fixing.
>
>I could not resist a bit of wordsmithing.  Could you please check to see if I messed something up?

Thanks wordsmithing, I think it's ok.

Thanks,
Zqiang

>
>							Thanx, Paul
>
>------------------------------------------------------------------------
>
>commit ad3c438e248cbc41fe30a41287621c3dbfcdf51c
>Author: Zqiang <qiang1.zhang@...el.com>
>Date:   Thu Mar 24 19:15:15 2022 +0800
>
>    rcu: Check for successful spawn of ->boost_kthread_task
>    
>    For the spawning of the priority-boost kthreads can fail, improbable
>    though this might seem.  This commit therefore refrains from attemoting
>    to initiate RCU priority boosting when The ->boost_kthread_task pointer
>    is NULL.
>    
>    Signed-off-by: Zqiang <qiang1.zhang@...el.com>
>    Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
>
>diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 6b9bcd45c7b2..d58f6d6073bf 100644
>--- a/kernel/rcu/tree_plugin.h
>+++ b/kernel/rcu/tree_plugin.h
>@@ -1125,7 +1125,8 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
> 	__releases(rnp->lock)
> {
> 	raw_lockdep_assert_held_rcu_node(rnp);
>-	if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
>+	if (!rnp->boost_kthread_task ||
>+	    (!rcu_preempt_blocked_readers_cgp(rnp) && !rnp->exp_tasks)) {
> 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
> 		return;
> 	}