linux-kernel - Re: [PATCH v2 rcu/dev 2/2] rcu: Disable laziness if lazy-tracking says so

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Message-ID: <20230115155455.0fb66c12@rorschach.local.home>
Date:   Sun, 15 Jan 2023 15:54:55 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org,
        fweisbec@...il.com, urezki@...il.com
Subject: Re: [PATCH v2 rcu/dev 2/2] rcu: Disable laziness if lazy-tracking
 says so

On Thu, 12 Jan 2023 00:52:23 +0000
"Joel Fernandes (Google)" <joel@...lfernandes.org> wrote:

>  
>  static void
> -__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy)
> +__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
>  {
>  	static atomic_t doublefrees;
>  	unsigned long flags;
>  	struct rcu_data *rdp;
> -	bool was_alldone;
> +	bool was_alldone, lazy;

I'm curious to why the the extra variable.

>  
>  	/* Misaligned rcu_head! */
>  	WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
> @@ -2622,6 +2622,7 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy)
>  	kasan_record_aux_stack_noalloc(head);
>  	local_irq_save(flags);
>  	rdp = this_cpu_ptr(&rcu_data);
> +	lazy = lazy_in && !rcu_async_should_hurry();

Wouldn't just having:

	lazy = lazy && !rcu_async_should_hurry();

be sufficient?

-- Steve

>  
>  	/* Add the callback to our list. */
>  	if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) {
> --