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

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Date:	Mon, 20 May 2013 12:12:40 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Li Zhong <zhong@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH nohz] return NOTIFY_BAD in cpu down call back to stop
 offlining the cpu

2013/5/20 Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>:
> 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>

I applied the patch and will send to Ingo, thanks guys!

>
>>  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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