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

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Date:	Mon, 24 Aug 2015 11:00:14 -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 08/23/2015 08:52 PM, 河合英宏 / KAWAI，HIDEHIRO wrote:
>> From: Corey Minyard [mailto:tcminyard@...il.com] On Behalf Of Corey Minyard
>>
>> 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.
> It may be so, but we should address this issue separately (at least
> I think above solution reasonably solves the issue).
>
> This issue happens after all queued messages are processed or dropped
> by timeout.  There is no current message.  So what should we set
> a timeout against?  We can add a timeout into my new flush_messages(),
> but that is meaningful only in panic context.  That doesn't help
> in normal context; we would perform a busy loop of smi_event_handler()
> and schedule() in ipmi_thread().

I'm a little confused here.  Is the problem that the ATN bit is stuck
high?  If so, it's going to be really hard to work around this without
breaking ATN handling.

-corey

>
> Regards,
>
> Hidehiro Kawai
>
>> 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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