linux-kernel - Re: [PATCH] keep rd->online and cpu_online

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Date:	Mon, 10 Mar 2008 11:12:45 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Gregory Haskins <ghaskins@...ell.com>
Cc:	ego@...ibm.com, suresh.b.siddha@...el.com, rjw@...k.pl,
	akpm@...ux-foundation.org, dmitry.adamushko@...il.com,
	mingo@...e.hu, oleg@...sign.ru, yi.y.yang@...el.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: Re: [PATCH] keep rd->online and cpu_online_map in sync

On Mon, Mar 10, 2008 at 09:39:34AM -0400, Gregory Haskins wrote:
> keep rd->online and cpu_online_map in sync
> 
> It is possible to allow the root-domain cache of online cpus to
> become out of sync with the global cpu_online_map.  This is because we
> currently trigger removal of cpus too early in the notifier chain.
> Other DOWN_PREPARE handlers may in fact run and reconfigure the
> root-domain topology, thereby stomping on our own offline handling.
> 
> The end result is that rd->online may become out of sync with
> cpu_online_map, which results in potential task misrouting.
> 
> So change the offline handling to be more tightly coupled with the
> global offline process by triggering on CPU_DYING intead of
> CPU_DOWN_PREPARE.
> 
> Signed-off-by: Gregory Haskins <ghaskins@...ell.com>
> ---
> 
>  kernel/sched.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 52b9867..a616fa1 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -5881,7 +5881,7 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
>  		spin_unlock_irq(&rq->lock);
>  		break;
>  
> -	case CPU_DOWN_PREPARE:
> +	case CPU_DYING:

Don't we need to take care of CPU_DYING_FROZEN aswell?

>  		/* Update our root-domain */
>  		rq = cpu_rq(cpu);
>  		spin_lock_irqsave(&rq->lock, flags);
> 
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