linux-kernel - Re: [PATCH v5 14/45] rcu, CPU hotplug: Fix comment referring to stop

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Message-ID: <20130209001439.GQ2666@linux.vnet.ibm.com>
Date:	Fri, 8 Feb 2013 16:14:39 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	tglx@...utronix.de, peterz@...radead.org, tj@...nel.org,
	oleg@...hat.com, rusty@...tcorp.com.au, mingo@...nel.org,
	akpm@...ux-foundation.org, namhyung@...nel.org,
	rostedt@...dmis.org, wangyun@...ux.vnet.ibm.com,
	xiaoguangrong@...ux.vnet.ibm.com, rjw@...k.pl, sbw@....edu,
	fweisbec@...il.com, linux@....linux.org.uk,
	nikunj@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 14/45] rcu, CPU hotplug: Fix comment referring to
 stop_machine()

On Tue, Jan 22, 2013 at 01:06:34PM +0530, Srivatsa S. Bhat wrote:
> Don't refer to stop_machine() in the CPU hotplug path, since we are going
> to get rid of it. Also, move the comment referring to callback adoption
> to the CPU_DEAD case, because that's where it happens now.
> 
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

Ouch!  That comment is indeed obsolete and must die.

I queued this to -rcu with your Signed-off-by.  However, I omitted
the added comment, as it is imcomplete -- it is easy to look at
rcu_cleanup_dead_cpu() to see what it does.

							Thanx, Paul

> ---
> 
>  kernel/rcutree.c |    9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index e441b77..ac94474 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -2827,11 +2827,6 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
>  		break;
>  	case CPU_DYING:
>  	case CPU_DYING_FROZEN:
> -		/*
> -		 * The whole machine is "stopped" except this CPU, so we can
> -		 * touch any data without introducing corruption. We send the
> -		 * dying CPU's callbacks to an arbitrarily chosen online CPU.
> -		 */
>  		for_each_rcu_flavor(rsp)
>  			rcu_cleanup_dying_cpu(rsp);
>  		rcu_cleanup_after_idle(cpu);
> @@ -2840,6 +2835,10 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
>  	case CPU_DEAD_FROZEN:
>  	case CPU_UP_CANCELED:
>  	case CPU_UP_CANCELED_FROZEN:
> +		/*
> +		 * We send the dead CPU's callbacks to an arbitrarily chosen
> +		 * online CPU.
> +		 */
>  		for_each_rcu_flavor(rsp)
>  			rcu_cleanup_dead_cpu(cpu, rsp);
>  		break;
> 

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