Rafael J. Wysocki wrote:
quoted text
> ..
>> @@ -879,6 +880,7 @@
>>  	if (pm_power_off_prepare)
>>  		pm_power_off_prepare();
>>  	sysdev_shutdown();
>> +	disable_nonboot_cpus();
> 
> Before sysdev_shutdown(), please.
> 
> sysdev_shutdown() may touch things that belong to CPU0.

Thanks.  Here is the revised patch.

* * *

We need to disable all CPUs other than the boot CPU (usually 0)
before attempting to power-off modern SMP machines.
This fixes the hang-on-poweroff issue on my MythTV SMP box,
and also on Thomas Gleixner's new toybox.

Signed-off-by: Mark Lord <mlord@pobox.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
---

--- linux/kernel/sys.c.orig	2007-09-13 09:49:11.000000000 -0400
+++ linux/kernel/sys.c	2007-09-28 15:48:54.000000000 -0400
@@ -32,6 +32,7 @@
 #include <linux/getcpu.h>
 #include <linux/task_io_accounting_ops.h>
 #include <linux/seccomp.h>
+#include <linux/cpu.h>
 
 #include <linux/compat.h>
 #include <linux/syscalls.h>
@@ -878,6 +879,7 @@
 	kernel_shutdown_prepare(SYSTEM_POWER_OFF);
 	if (pm_power_off_prepare)
 		pm_power_off_prepare();
+	disable_nonboot_cpus();
 	sysdev_shutdown();
 	printk(KERN_EMERG "Power down.\n");
 	machine_power_off();
-
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