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SubjectRe: [PATCH v4 3/5] acpi_processor: do not mark present at boot but not onlined CPU as onlined
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On Fri, 2014-05-02 at 13:32 +0200, Igor Mammedov wrote:
> On Wed, 30 Apr 2014 15:25:51 -0600
> Toshi Kani <toshi.kani@hp.com> wrote:
>
> > On Mon, 2014-04-14 at 17:11 +0200, Igor Mammedov wrote:
> > > acpi_processor_add() assumes that present at boot CPUs
> > > are always onlined, it is not so if a CPU failed to become
> > > onlined. As result acpi_processor_add() will mark such CPU
> > > device as onlined in sysfs and following attempts to
> > > online/offline it using /sys/device/system/cpu/cpuX/online
> > > attribute will fail.
> > >
> > > Do not poke into device internals in acpi_processor_add()
> > > and touch "struct device { .offline }" attribute, since
> > > for CPUs onlined at boot it's set by:
> > > topology_init() -> arch_register_cpu() -> register_cpu()
> > > before ACPI device tree is parsed, and for hotplugged
> > > CPUs it's set when userspace onlines CPU via sysfs.
> > >
> > > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > > ---
> > > v2:
> > > - fix regression in v1 leading to NULL pointer dereference
> > > on CPU unplug, do not remove "pr->dev = dev;"
> > > ---
> > > drivers/acpi/acpi_processor.c | 1 -
> > > 1 files changed, 0 insertions(+), 1 deletions(-)
> > >
> > > diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> > > index c29c2c3..42d66f8 100644
> > > --- a/drivers/acpi/acpi_processor.c
> > > +++ b/drivers/acpi/acpi_processor.c:q
> > > @@ -404,7 +404,6 @@ static int acpi_processor_add(struct acpi_device *device,
> > > goto err;
> > >
> > > pr->dev = dev;
> > > - dev->offline = pr->flags.need_hotplug_init;
> >
> > IIRC, this change was necessary to handle the case when maxcpus=X is
> > specified at boot. In this case, excessive CPU's dev->offline needs to
> > be set to 1. Can you verify this?
> Option 'maxcpus' works just fine without and with this patch since a bit
> earlier in acpi_processor_add() it exits in case of extra present CPUs:
>
> #ifdef CONFIG_SMP
> if (pr->id >= setup_max_cpus && pr->id != 0)
> return 0;
> #endif
>
> and execution doesn't get to the point the patch touches.

This is a separate topic, but I feel that the above code should not be
necessary...

> The point is that acpi_processor_add() shouldn't touch
> dev->offline at all and allow register_cpu() handle it.

Sorry, I had confused with cpu->dev.offline in register_cpu() in my
recollection. Yes, I agree that we should let register_cpu() to handle
it.

Acked-by: Toshi Kani <toshi.kani@hp.com>

Thanks,
-Toshi







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