linux-kernel - Re: [PATCH 08/16] rcu/nocb: Move trace_rcu_nocb_wake() calls outside nocb

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Date:   Thu, 28 Jan 2021 16:51:28 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Josh Triplett <josh@...htriplett.org>,
        Stable <stable@...r.kernel.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 08/16] rcu/nocb: Move trace_rcu_nocb_wake() calls outside
 nocb_lock when possible

On Thu, Jan 28, 2021 at 06:12:14PM +0100, Frederic Weisbecker wrote:
> Those tracing calls don't need to be under the nocb lock. Move them
> outside.

This one looks fine (give or take the usual wordsmithing), but does
not apply, presumably due to my not having yet taken one of the earlier
patches.  So deferred for now, and please include it in your next version.

							Thanx, Paul

> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> Cc: Josh Triplett <josh@...htriplett.org>
> Cc: Lai Jiangshan <jiangshanlai@...il.com>
> Cc: Joel Fernandes <joel@...lfernandes.org>
> Cc: Neeraj Upadhyay <neeraju@...eaurora.org>
> Cc: Boqun Feng <boqun.feng@...il.com>
> ---
>  kernel/rcu/tree_plugin.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 86c3bcceede6..8c5fea58ee80 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -1700,9 +1700,9 @@ static bool wake_nocb_gp(struct rcu_data *rdp, bool force,
>  
>  	lockdep_assert_held(&rdp->nocb_lock);
>  	if (!READ_ONCE(rdp_gp->nocb_gp_kthread)) {
> +		rcu_nocb_unlock_irqrestore(rdp, flags);
>  		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
>  				    TPS("AlreadyAwake"));
> -		rcu_nocb_unlock_irqrestore(rdp, flags);
>  		return false;
>  	}
>  
> @@ -1950,9 +1950,9 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
>  	// If we are being polled or there is no kthread, just leave.
>  	t = READ_ONCE(rdp->nocb_gp_kthread);
>  	if (rcu_nocb_poll || !t) {
> +		rcu_nocb_unlock_irqrestore(rdp, flags);
>  		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
>  				    TPS("WakeNotPoll"));
> -		rcu_nocb_unlock_irqrestore(rdp, flags);
>  		return;
>  	}
>  	// Need to actually to a wakeup.
> @@ -1987,8 +1987,8 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
>  					   TPS("WakeOvfIsDeferred"));
>  		rcu_nocb_unlock_irqrestore(rdp, flags);
>  	} else {
> +		rcu_nocb_unlock_irqrestore(rdp, flags);
>  		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
> -		rcu_nocb_unlock_irqrestore(rdp, flags);
>  	}
>  	return;
>  }
> -- 
> 2.25.1
>