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: <55CAC849.70902@acm.org>
Date:	Tue, 11 Aug 2015 23:15:05 -0500
From:	Corey Minyard <minyard@....org>
To:	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
CC:	openipmi-developer@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] ipmi/kcs: Don't run the KCS state machine when it
 is KCS_IDLE

This patch will break ATN handling on the interfaces.  So we can't do this.

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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