linux-kernel - Re: [PATCH v2] rcu, kasan: Record work creation stack trace with interrupts enabled

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Message-ID: <20211228161749.GW4109570@paulmck-ThinkPad-P17-Gen-1>
Date:   Tue, 28 Dec 2021 08:17:49 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Zqiang <qiang1.zhang@...el.com>
Cc:     elver@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] rcu, kasan: Record work creation stack trace with
 interrupts enabled

On Sun, Dec 26, 2021 at 08:52:04AM +0800, Zqiang wrote:
> Recording the work creation stack trace for KASAN reports in
> call_rcu() is expensive, due to unwinding the stack, but also
> due to acquiring depot_lock inside stackdepot (which may be contended).
> Because calling kasan_record_aux_stack_noalloc() does not require
> interrupts to already be disabled, this may unnecessarily extend
> the time with interrupts disabled.
> 
> Therefore, move calling kasan_record_aux_stack() before the section
> with interrupts disabled.
> 
> Acked-by: Marco Elver <elver@...gle.com>
> Signed-off-by: Zqiang <qiang1.zhang@...el.com>

Applied, thank you both!

							Thanx, Paul

> ---
>  v1->v2:
>  Make the submitted information clearer.
> 
>  kernel/rcu/tree.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 9b58bae0527a..36bd3f9e57b3 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -3068,8 +3068,8 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func)
>  	}
>  	head->func = func;
>  	head->next = NULL;
> -	local_irq_save(flags);
>  	kasan_record_aux_stack_noalloc(head);
> +	local_irq_save(flags);
>  	rdp = this_cpu_ptr(&rcu_data);
>  
>  	/* Add the callback to our list. */
> -- 
> 2.25.1
>