On Mon, 2013-06-03 at 18:43 +0800, Zhao Chenhui wrote:
> On Sat, Jun 01, 2013 at 07:49:44AM +1000, Benjamin Herrenschmidt wrote:
> > On Tue, 2013-05-28 at 15:59 +0800, Zhao Chenhui wrote:
> > > Some features depend on the boot cpu, for instance, hibernate/suspend.
> > > So disable hotplug for the boot cpu.
> >
> > Don't we have code to "move" the boot CPU around when that happens ?
> >
> > Ben.
> >
>
> Currently, the code in generic_cpu_disable() likes this:
>
> if (cpu == boot_cpuid)
>
> return -EBUSY;
But the code in pseries/hotplug-cpu.c doesn't, we just "move" the boot
CPU around when that happens. Any reason we can't do that generically ?
Cheers,
Ben.
> If the dying cpu is the boot cpu, it will return -EBUSY. In the subsequent
> error handling,
> cpu_notify_nofail(CPU_DOWN_FAILED) in _cpu_down() will be called.
> Unfortunately, some
> cpu notifier callbacks handled CPU_DOWN_PREPARE, but not CPU_DOWN_FAILED,
> such as sched_cpu_inactive().
> So it will cause issues.
>
> If we set the hotpluggable for the boot cpu, we can prevent user applications
> from disabling the boot cpu.
>
> -Chenhui
>
> > > Signed-off-by: Zhao Chenhui <chenhui.z...@freescale.com>
> > > ---
> > > arch/powerpc/kernel/sysfs.c | 4 +++-
> > > 1 files changed, 3 insertions(+), 1 deletions(-)
> > >
> > > diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
> > > index e68a845..294b1c4e 100644
> > > --- a/arch/powerpc/kernel/sysfs.c
> > > +++ b/arch/powerpc/kernel/sysfs.c
> > > @@ -655,8 +655,10 @@ static int __init topology_init(void)
> > > * CPU. For instance, the boot cpu might never be valid
> > > * for hotplugging.
> > > */
> > > - if (ppc_md.cpu_die)
> > > + if (ppc_md.cpu_die && cpu != boot_cpuid)
> > > c->hotpluggable = 1;
> > > + else
> > > + c->hotpluggable = 0;
> > >
> > > if (cpu_online(cpu) || c->hotpluggable) {
> > > register_cpu(c, cpu);
> >
> >
> >
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