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;
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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