linux-kernel - Re: [PATCH] kernel/watchdog.c: Only output hw-PMU message once

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Date:   Mon, 21 Nov 2016 12:59:47 -0500
From:   Prarit Bhargava <prarit@...hat.com>
To:     Don Zickus <dzickus@...hat.com>
CC:     linux-kernel@...r.kernel.org, Borislav Petkov <bp@...e.de>,
        Tejun Heo <tj@...nel.org>,
        Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <ak@...ux.intel.com>,
        Joshua Hunt <johunt@...mai.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] kernel/watchdog.c: Only output hw-PMU message once



On 11/21/2016 12:48 PM, Don Zickus wrote:
> On Mon, Nov 21, 2016 at 11:35:19AM -0500, Prarit Bhargava wrote:
>> When CONFIG_BOOTPARAM_HOTPLUG_CPU0 is enabled, the socket containing the
>> boot cpu can be replaced.  During the hot add event, the message
>>
>> NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter.
>>
>> is output implying that the NMI was disabled at some point.  This is not the
>> case and the message has caused confusion for users of systems that support
>> socket removal.
>>
>> This patch modifies the message so that it only outputs a single time
>> during runtime.
> 
> Hmm, it occurred to me, with pr_info_once, what happens if you disable and
> re-enable, is this still printed?
> 
> echo 0 > /proc/sys/kernel/watchdog
> echo 1 > /proc/sys/kernel/watchdog

With my patch, the message is not printed using the above steps.  I'll go back
and see if I can figure something out.

P.

> 
> Cheers,
> Don
> 
>>
>> Signed-off-by: Prarit Bhargava <prarit@...hat.com>
>> Cc: Borislav Petkov <bp@...e.de>
>> Cc: Tejun Heo <tj@...nel.org>
>> Cc: Don Zickus <dzickus@...hat.com>
>> Cc: Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Andi Kleen <ak@...ux.intel.com>
>> Cc: Joshua Hunt <johunt@...mai.com>
>> Cc: Ingo Molnar <mingo@...nel.org>
>> ---
>>  kernel/watchdog.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
>> index 9acb29f280ec..560414692c01 100644
>> --- a/kernel/watchdog.c
>> +++ b/kernel/watchdog.c
>> @@ -615,7 +615,7 @@ static int watchdog_nmi_enable(unsigned int cpu)
>>  	if (!IS_ERR(event)) {
>>  		/* only print for cpu0 or different than cpu0 */
>>  		if (cpu == 0 || cpu0_err)
>> -			pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
>> +			pr_info_once("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
>>  		goto out_save;
>>  	}
>>  
>> -- 
>> 1.7.9.3
>>