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SubjectRe: + pm-introduce-new-interfaces-schedule_work_on-and-queue_work_on.patch added to -mm tree
On 07/22, Gautham R Shenoy wrote:
>
> On Sat, Jul 12, 2008 at 08:21:49PM +0400, Oleg Nesterov wrote:
> >
> > So, this is used in http://bugzilla.kernel.org/attachment.cgi?id=16707
> >
> > --- linux-2.6.orig/kernel/power/poweroff.c 2008-06-30 16:01:35.000000000 +0800
> > +++ linux-2.6/kernel/power/poweroff.c 2008-07-03 10:50:05.000000000 +0800
> > @@ -25,7 +25,8 @@
> >
> > static void handle_poweroff(int key, struct tty_struct *tty)
> > {
> > - schedule_work(&poweroff_work);
> > + /* run sysrq poweroff on boot cpu */
> > + schedule_work_on(first_cpu(cpu_online_map), &poweroff_work);
> > }
> >
> > static struct sysrq_key_op sysrq_poweroff_op = {
> >
> > A couple of silly questions, I don't understand the low-level details.
> >
> > This patch (and kernel_power_off() afaics) assumes that the boot cpu
> > can't be cpu_down()'ed. Is it true in general? For example, grep shows
> > that arch/s390/kernel/smp.c:topology_init()->smp_add_present_cpu()
> > sets ->hotpluggable = 1 for all present CPUs?
>
> I tried this on a Power system sometime back and I was able to
> offline CPU0.

This means that

pm-schedule-sysrq-poweroff-on-boot-cpu.patch

is not 100% right. It is still possible to hang/deadlock if we race
with cpu_down(first_cpu(cpu_online_map)).

The bug is mostly theoretical, but perhaps should be fixed anyway,
handle_poweroff() can use kthread_run().

Oleg.



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