Mark Lord wrote:
quoted text
> 
> We need to disable all CPUs other than the boot CPU (usually 0)
> before attempting to power-off modern SMP machines.
> This seems to fix the hang-on-poweroff issue
> that one of my SMP boxes exhibits.  More testing required.
> 
> Signed-off-by: Mark Lord <mlord@pobox.com>
> ---
> 
> --- linux/kernel/sys.c.orig    2007-09-13 09:49:11.000000000 -0400
> +++ linux/kernel/sys.c    2007-09-28 09:48:54.000000000 -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>
> @@ -879,6 +880,7 @@
>     if (pm_power_off_prepare)
>         pm_power_off_prepare();
>     sysdev_shutdown();
> +    disable_nonboot_cpus();
>     printk(KERN_EMERG "Power down.\n");
>     machine_power_off();
> }

Okay, verified now.  Prior to this patch, *both* CPUs were still up and running
when machine_power_off() got called, and there was no guarantee that CPU0 was
the one calling machine_power_off().   BUG.

The above patch guarantees that only the single boot CPU is running
and calling machine_power_off().

Hopefully this buries the SMP-power-off bogeyman for good!

Cheers
-
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