linux-kernel - Re: [PATCH] kernel/sysrq: reset watchdog on all CPUs while processing sysrq-w

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Date:	Wed, 8 Jun 2016 17:39:45 +0300
From:	Andrey Ryabinin <aryabinin@...tuozzo.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel/sysrq: reset watchdog on all CPUs while processing
 sysrq-w



On 06/08/2016 04:13 PM, Ingo Molnar wrote:
> 
> * Andrey Ryabinin <aryabinin@...tuozzo.com> wrote:
> 
>> Lengthy output of sysrq-w may take a lot of time on slow serial console.
>> Currently we reset NMI-watchdog on the current CPU to avoid softlockup.
>> Sometimes this doesn't work since watchdog might trigger on the other
>> CPU which is waiting for an IPI to proceed.
>>
>> Reset watchdog on all CPUs to prevent spurious softlockup messages.
>>
>> Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
>> ---
>>  kernel/sched/core.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 7f2cae4..c135eee 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -5134,7 +5134,7 @@ void show_state_filter(unsigned long state_filter)
>>  		 * reset the NMI-timeout, listing all files on a slow
>>  		 * console might take a lot of time:
>>  		 */
>> -		touch_nmi_watchdog();
>> +		touch_all_softlockup_watchdogs();
> 
> So don't we want both?
> 

Indeed, we need both.
I was under the false impression that touch_all_softlockup_watchdogs() will reset NMI timeout too

> Thanks,
> 
> 	Ingo
>