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

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Message-ID: <55DE2127.3010402@acm.org>
Date:	Wed, 26 Aug 2015 15:27:19 -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 08/24/2015 10:53 PM, 河合英宏 / KAWAI，HIDEHIRO wrote:
>> From: Corey Minyard [mailto:tcminyard@...il.com] On Behalf Of Corey Minyard
>>
>> 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.
> Sorry for my insufficient explanation.  I assume the case where
> IBF bit is always 1.  I don't know what happens when
> BMC hangs up, but I guess IBF stays in 1 because my server's
> BMC behaves as such while rebooting.
>
Ok, your patch above makes sense, then.  IBF is irrelevant when in idle
state,
so ignore it then, and then in your case it will return KCS_IDLE and
cause that
operation to complete.  I'm ok with the patch you posted above, I think
it will
work correctly and solve the problem.

I would like a detailed comment, though, so people (forgetful people
like me :)
can figure out why it is there.  I'd also like to save this one until
4.4 to give it some
time in linux-next for people to find issues.

Thanks,

-corey
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