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From:   Uladzislau Rezki <urezki@gmail.com>
Date:   Fri, 14 Aug 2020 20:51:24 +0200
To:     qiang.zhang@windriver.com, Joel Fernandes <joel@joelfernandes.org>
Cc:     paulmck@kernel.org, josh@joshtriplett.org, rostedt@goodmis.org,
        mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
        joel@joelfernandes.org, rcu@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] rcu: shrink each possible cpu krcp
Message-ID: <20200814185124.GA2113@pc636>
References: <20200814064557.17365-1-qiang.zhang@windriver.com>
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> From: Zqiang <qiang.zhang@windriver.com>
> 
> Due to cpu hotplug. some cpu may be offline after call "kfree_call_rcu"
> func, if the shrinker is triggered at this time, we should drain each
> possible cpu "krcp".
> 
> Signed-off-by: Zqiang <qiang.zhang@windriver.com>
> ---
>  kernel/rcu/tree.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 8ce77d9ac716..619ccbb3fe4b 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -3443,7 +3443,7 @@ kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
>  	unsigned long count = 0;
>  
>  	/* Snapshot count of all CPUs */
> -	for_each_online_cpu(cpu) {
> +	for_each_possible_cpu(cpu) {
>  		struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
>  
>  		count += READ_ONCE(krcp->count);
> @@ -3458,7 +3458,7 @@ kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
>  	int cpu, freed = 0;
>  	unsigned long flags;
>  
> -	for_each_online_cpu(cpu) {
> +	for_each_possible_cpu(cpu) {
>  		int count;
>  		struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
>  
> @@ -3491,7 +3491,7 @@ void __init kfree_rcu_scheduler_running(void)
>  	int cpu;
>  	unsigned long flags;
>  
> -	for_each_online_cpu(cpu) {
> +	for_each_possible_cpu(cpu) {
>  		struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
>  
>  		raw_spin_lock_irqsave(&krcp->lock, flags);
>
I agree that it can happen.

Joel, what is your view?

Thanks!

--
Vlad Rezki