Date: Mon, 10 Mar 2008 11:12:45 -0700
From: Suresh Siddha <suresh.b.siddha@intel.com>
To: Gregory Haskins <ghaskins@novell.com>
Cc: ego@in.ibm.com, suresh.b.siddha@intel.com, rjw@sisk.pl,
       akpm@linux-foundation.org, dmitry.adamushko@gmail.com, mingo@elte.hu,
       oleg@sign.ru, yi.y.yang@intel.com, linux-kernel@vger.kernel.org,
       tglx@linutronix.de
Subject: Re: [PATCH] keep rd->online and cpu_online_map in sync
Message-ID: <20080310181244.GA27329@linux-os.sc.intel.com>
References: <20080310081425.GA11031@in.ibm.com> <20080310133755.4689.83217.stgit@novell1.haskins.net>
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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@novell.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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