linux-kernel - Re: [PATCH 3/3] rcu: Report callbacks enqueued on offline CPU blind spot

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Message-ID: <Zv1f8-1tLd-r1cyu@localhost.localdomain>
Date: Wed, 2 Oct 2024 17:00:03 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Boqun Feng <boqun.feng@...il.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Neeraj Upadhyay <neeraj.upadhyay@....com>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>, rcu <rcu@...r.kernel.org>
Subject: Re: [PATCH 3/3] rcu: Report callbacks enqueued on offline CPU blind
 spot

Le Wed, Oct 02, 2024 at 04:57:38PM +0200, Frederic Weisbecker a écrit :
> Callbacks enqueued after rcutree_report_cpu_dead() fall into RCU barrier
> blind spot. Report any potential misuse.
> 
> Reported-by: Paul E. McKenney <paulmck@...nel.org>
> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> ---
>  kernel/rcu/tree.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index a60616e69b66..36070b6bf4a1 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -3084,8 +3084,11 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
>  	head->func = func;
>  	head->next = NULL;
>  	kasan_record_aux_stack_noalloc(head);
> +
>  	local_irq_save(flags);
>  	rdp = this_cpu_ptr(&rcu_data);
> +	RCU_LOCKDEP_WARN(rcu_rdp_cpu_online(rdp), "Callback enqueued on offline
> CPU!");

This should be !rcu_rdp_cpu_online(rdp)

Sigh...

> +
>  	lazy = lazy_in && !rcu_async_should_hurry();
>  
>  	/* Add the callback to our list. */
> -- 
> 2.46.0
> 
>