Message-ID: <55DE2127.3010402@acm.org>
Date: Wed, 26 Aug 2015 15:27:19 -0500
From: Corey Minyard <minyard@acm.org>
Reply-To: minyard@acm.org
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0
MIME-Version: 1.0
To: =?UTF-8?B?5rKz5ZCI6Iux5a6PIC8gS0FXQUnvvIxISURFSElSTw==?= 
	<hidehiro.kawai.ez@hitachi.com>
CC: "openipmi-developer@lists.sourceforge.net" 
	<openipmi-developer@lists.sourceforge.net>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 7/7] ipmi/kcs: Don't run the KCS state machine when it
 is KCS_IDLE
References: <20150727055516.4759.34462.stgit@softrs> <20150727055516.4759.65106.stgit@softrs> <55CAC849.70902@acm.org> <04EAB7311EE43145B2D3536183D1A84454938089@GSjpTKYDCembx31.service.hitachi.net> <55D8B543.4000805@acm.org> <04EAB7311EE43145B2D3536183D1A8445493D025@GSjpTKYDCembx31.service.hitachi.net> <55DB3F8E.5030100@acm.org> <04EAB7311EE43145B2D3536183D1A8445495009D@GSjpTKYDCembx31.service.hitachi.net>
In-Reply-To: <04EAB7311EE43145B2D3536183D1A8445495009D@GSjpTKYDCembx31.service.hitachi.net>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2692
Lines: 59

On 08/24/2015 10:53 PM, 河合英宏 / KAWAI，HIDEHIRO wrote:
>> From: Corey Minyard [mailto:tcminyard@gmail.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@gmail.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@gmail.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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/