linux-kernel - Re: [PATCH 7/7] ipmi/kcs: Don't run the KCS state machine when it is KCS

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Date:	Sat, 22 Aug 2015 12:45:39 -0500
From:	Corey Minyard <minyard@....org>
To:	河合英宏 / KAWAI，HIDEHIRO 
	<hidehiro.kawai.ez@...achi.com>
CC:	"openipmi-developer@...ts.sourceforge.net" 
	<openipmi-developer@...ts.sourceforge.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/7] ipmi/kcs: Don't run the KCS state machine when it
 is KCS_IDLE

On 08/17/2015 09:54 PM, 河合英宏 / KAWAI，HIDEHIRO wrote:
>> From: Corey Minyard [mailto:tcminyard@...il.com] On Behalf Of Corey Minyard
>>
>> This patch will break ATN handling on the interfaces.  So we can't do this.
> I understand.  So how about doing like this:
>
> 	/* All states wait for ibf, so just do it here. */
> -	if (!check_ibf(kcs, status, time))
> +	if (kcs->state != KCS_IDLE && !check_ibf(kcs, status, time))
> 		return SI_SM_CALL_WITH_DELAY;
>
> I think it is not necessary to wait IBF when the state is IDLE.
> In this way, we can also handle the ATN case.

I think it would be more reliable to go up a level and add a timeout. 
One should
be there, anyway.  I thought they were all covered, but I may have missed
something.

-corey

>
> Regards,
>
> Hidehiro Kawai
> Hitachi, Ltd. Research & Development Group
>
>> It's going to be extremely hard to recover if the BMC is not working
>> correctly when a panic happens.  I'm not sure what can be done, but if
>> you can fix it another way it would be good.
>>
>> -corey
>>
>> On 07/27/2015 12:55 AM, Hidehiro Kawai wrote:
>>> If a BMC is unresponsive for some reason, it ends up completing
>>> the requested message as an error, then kcs_event() is called once
>>> to advance the state machine.  However, since the BMC is
>>> unresponsive now, the status of the KCS interface may not be
>>> idle.  As the result, the state machine can continue to run and
>>> comsume CPU time indefinitely even if there is no more request
>>> message.  Moreover, if this happens in run-to-completion mode
>>> (i.e. context of panic_event()), the kernel hangs up.
>>>
>>> To fix this problem, this patch ignores kcs_event() call if there
>>> is no request message to be processed.
>>>
>>> Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
>>> ---
>>>  drivers/char/ipmi/ipmi_kcs_sm.c |    4 ++++
>>>  1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/char/ipmi/ipmi_kcs_sm.c b/drivers/char/ipmi/ipmi_kcs_sm.c
>>> index 8c25f59..0e187fb 100644
>>> --- a/drivers/char/ipmi/ipmi_kcs_sm.c
>>> +++ b/drivers/char/ipmi/ipmi_kcs_sm.c
>>> @@ -353,6 +353,10 @@ static enum si_sm_result kcs_event(struct si_sm_data *kcs, long time)
>>>  	if (kcs_debug & KCS_DEBUG_STATES)
>>>  		printk(KERN_DEBUG "KCS: State = %d, %x\n", kcs->state, status);
>>>
>>> +	/* We don't want to run the state machine when the state is IDLE */
>>> +	if (kcs->state == KCS_IDLE)
>>> +		return SI_SM_IDLE;
>>> +
>>>  	/* All states wait for ibf, so just do it here. */
>>>  	if (!check_ibf(kcs, status, time))
>>>  		return SI_SM_CALL_WITH_DELAY;
>>>
>>>

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