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

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Message-ID: <20150727055516.4759.65106.stgit@softrs>
Date:	Mon, 27 Jul 2015 14:55:16 +0900
From:	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
To:	Corey Minyard <minyard@....org>
Cc:	openipmi-developer@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: [PATCH 7/7] ipmi/kcs: Don't run the KCS state machine when it is
 KCS_IDLE

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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