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

[Corey Minyard <minyard@acm.org>]

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@hitachi.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;
>
>