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: <04EAB7311EE43145B2D3536183D1A84454938089@GSjpTKYDCembx31.service.hitachi.net>
Date:	Tue, 18 Aug 2015 02:54:19 +0000
From:	河合英宏 / KAWAI，HIDEHIRO 
	<hidehiro.kawai.ez@...achi.com>
To:	"'minyard@....org'" <minyard@....org>
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

> 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.

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;
> >
> >