linux-kernel - Re: [RFC PATCH nohz] return NOTIFY_BAD in cpu down call back to stop offlining the cpu

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Message-ID: <5199F1E9.2080002@linux.vnet.ibm.com>
Date:	Mon, 20 May 2013 15:20:33 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Li Zhong <zhong@...ux.vnet.ibm.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [RFC PATCH nohz] return NOTIFY_BAD in cpu down call back to stop
 offlining the cpu

On 05/17/2013 02:14 PM, Li Zhong wrote:
> In tick_nohz_cpu_down_callback() if the cpu is the one handling
> timekeeping , it seems that we should return something that could stop
> notify CPU_DOWN_PREPARE, and then start notify CPU_DOWN_FAILED on the
> already called notifier call backs.
> 
> -EINVAL will be converted to 0 by notifier_to_errno(),

This above line is not relevant here, because notifier_call_chain()
doesn't use notifier_to/from_errno(). It simply uses a straight-forward
check like this:

if ((ret & NOTIFY_STOP_MASK) == NOTIFY_STOP_MASK)
	break;

> then the cpu
> would be taken down with part of the DOWN_PREPARE notifier callbacks
> called, and something bad could happen after that.
> 
> Signed-off-by: Li Zhong <zhong@...ux.vnet.ibm.com>
> ---

Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

>  kernel/time/tick-sched.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index bc67d42..17b8155 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -306,7 +306,7 @@ static int __cpuinit tick_nohz_cpu_down_callback(struct notifier_block *nfb,
>  		 * we can't safely shutdown that CPU.
>  		 */
>  		if (have_nohz_full_mask && tick_do_timer_cpu == cpu)
> -			return -EINVAL;
> +			return NOTIFY_BAD;
>  		break;
>  	}
>  	return NOTIFY_OK;
> 
 
Regards,
Srivatsa S. Bhat

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