ipmi:si: Fix check for a misbehaving BMC

There is a race on checking the state in the sender, it needs to be
checked under a lock.  But you also need a check to avoid issues with
a misbehaving BMC for run to completion mode.  So leave the check at
the beginning for run to completion, and add a check under the lock
to avoid the race.

Reported-by: Rafael J. Wysocki <rafael@kernel.org>
Fixes: bc3a9d2 ("ipmi:si: Gracefully handle if the BMC is non-functional")
Cc: stable@vger.kernel.org # 4.18
Signed-off-by: Corey Minyard <corey@minyard.net>
Reviewed-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>

Author: cminyard

drivers/char/ipmi/ipmi_si_intf.c

@@ -924,9 +924,14 @@ static int sender(void *send_info, struct ipmi_smi_msg *msg)
 {
 	struct smi_info   *smi_info = send_info;
 	unsigned long     flags;
+	int rv = IPMI_CC_NO_ERROR;
 
 	debug_timestamp(smi_info, "Enqueue");
 
+	/*
+	 * Check here for run to completion mode.  A check under lock is
+	 * later.
+	 */
 	if (smi_info->si_state == SI_HOSED)
 		return IPMI_BUS_ERR;
 
@@ -940,18 +945,15 @@ static int sender(void *send_info, struct ipmi_smi_msg *msg)
 	}
 
 	spin_lock_irqsave(&smi_info->si_lock, flags);
-	/*
-	 * The following two lines don't need to be under the lock for
-	 * the lock's sake, but they do need SMP memory barriers to
-	 * avoid getting things out of order.  We are already claiming
-	 * the lock, anyway, so just do it under the lock to avoid the
-	 * ordering problem.
-	 */
-	BUG_ON(smi_info->waiting_msg);
-	smi_info->waiting_msg = msg;
-	check_start_timer_thread(smi_info);
+	if (smi_info->si_state == SI_HOSED) {
+		rv = IPMI_BUS_ERR;
+	} else {
+		BUG_ON(smi_info->waiting_msg);
+		smi_info->waiting_msg = msg;
+		check_start_timer_thread(smi_info);
+	}
 	spin_unlock_irqrestore(&smi_info->si_lock, flags);
-	return IPMI_CC_NO_ERROR;
+	return rv;
 }
 
 static void set_run_to_completion(void *send_info, bool i_run_to_completion)