linux-kernel - Re: [PATCH 03/10] rcu: Make locking explicit in do_nocb_deferred_wakeup

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Message-ID: <20200526195928.GC149611@google.com>
Date:   Tue, 26 May 2020 15:59:28 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     "Paul E . McKenney" <paulmck@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Josh Triplett <josh@...htriplett.org>
Subject: Re: [PATCH 03/10] rcu: Make locking explicit in
 do_nocb_deferred_wakeup_common()

On Wed, May 13, 2020 at 06:47:07PM +0200, Frederic Weisbecker wrote:
> It can either be called inline (locally or CPU hotplug locked) when
> rdp->nocb_defer_wakeup is pending or from the nocb timer. In both cases
> the rdp is offlined and we want to take the nocb lock.

s/offlined/offloaded/

thanks,

 - Joel

> 
> Clarify the locking rules and expectations.
> 
> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> Cc: Paul E. McKenney <paulmck@...nel.org>
> Cc: Josh Triplett <josh@...htriplett.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: Lai Jiangshan <jiangshanlai@...il.com>
> Cc: Joel Fernandes <joel@...lfernandes.org>
> ---
>  kernel/rcu/tree_plugin.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 1d22b16c03e0..1dd3fdd675a1 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2142,9 +2142,9 @@ static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
>  	unsigned long flags;
>  	int ndw;
>  
> -	rcu_nocb_lock_irqsave(rdp, flags);
> +	raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
>  	if (!rcu_nocb_need_deferred_wakeup(rdp)) {
> -		rcu_nocb_unlock_irqrestore(rdp, flags);
> +		raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
>  		return;
>  	}
>  	ndw = READ_ONCE(rdp->nocb_defer_wakeup);
> -- 
> 2.25.0
>