[RFC PATCH nohz] return NOTIFY_BAD in cpu down call back to stop offlining the cpu

[RFC PATCH nohz] return NOTIFY_BAD in cpu down call back to stop offlining the cpu

[Li Zhong]

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(), 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@linux.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;
-- 
1.7.1

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

[Srivatsa S. Bhat]

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@linux.vnet.ibm.com>
> ---

Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.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

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

[Frederic Weisbecker]

2013/5/20 Srivatsa S. Bhat <srivatsa.bhat@linux.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@linux.vnet.ibm.com>
>> ---
>
> Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.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
>