Re: cpu hotplug: possible_cpus broken (again?) next-20130607

[Youquan Song <youquan.song@linux.intel.com>]

On Tue, Jun 11, 2013 at 04:32:34PM -0600, Toshi Kani wrote:
> On Wed, 2013-06-12 at 00:34 +0200, Rafael J. Wysocki wrote:
> > On Tuesday, June 11, 2013 03:17:28 PM Dave Hansen wrote:
> > > On 06/11/2013 03:05 PM, Rafael J. Wysocki wrote:
> > > > On Tuesday, June 11, 2013 02:51:33 PM Dave Hansen wrote:
> > > >> possible_cpus looks broken again.  I'm booting with:
> > > >>
> > > >>  maxcpus=10 possible_cpus=160
> > > >>
> > > >> But I only get 0-9 in sysfs:
> > > >>
> > > >>> # ls /sys/devices/system/cpu/
> > > >>> cpu0  cpu2  cpu4  cpu6  cpu8  cpufreq  kernel_max  offline  possible  probe    uevent
> > > >>> cpu1  cpu3  cpu5  cpu7  cpu9  cpuidle  modalias    online   present   release
> > > > 
> > > > Can you please test the acpi-hotplug branch of the linux-pm.git tree?
> > > 
> > > That branch seems to work happily.
> > 
> > In that case the problem may have been reintroduced by a merge conflict fix in
> > linux-next.
> 
> I believe the problem was introduced by the following change.  From the
> description, though, this is exactly what this patch was trying to
> change...  Adding Youguan to the list.
> 
> commit 3e275a5ba367ab74b3a4e49114307baed989fcac
> Author: Youquan Song <youquan.song@intel.com>
> Date:   Fri Jun 7 10:07:08 2013 +1000
> 
>     drivers/base/cpu.c: fix maxcpus boot option
> 
Hi Toshi,

Thanks Thoshi for the information.
please try the below patch to fix the issue by moving the code to
store_online.

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 3d48fc8..2378f42 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -60,6 +60,13 @@ static ssize_t __ref store_online(struct device *dev,
                        kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
                break;
        case '1':
+#ifdef CONFIG_SMP
+              /* return when cpu number greater than maximum number of
CPUs */
+               if (setup_max_cpus <= num_online_cpus() + 1) {
+                       cpu_hotplug_driver_unlock();
+                       return -EINVAL;
+               }
+#endif
                from_nid = cpu_to_node(cpuid);
                ret = cpu_up(cpuid);

Thanks
-Youquan