[PATCH] ACPI, cpu hotplug: move try_offline_node() after acpi_unmap_lsapic()

[PATCH] ACPI, cpu hotplug: move try_offline_node() after acpi_unmap_lsapic()

[Yasuaki Ishimatsu]

try_offline_node() checks that all cpus related with removed node have been
removed by using cpu_present_bits. If all cpus related with removed node have
been removed, try_offline_node() clears the node information.

But try_offline_node() called from acpi_processor_remove() never clears
the node information. For disabling cpu_present_bits, acpi_unmap_lsapic()
need be called. But acpi_unmap_lsapic() is called after try_offline_node()
runs. So when try_offline_node() runs, the cpu's cpu_present_bits is always
set.

This patch moves try_offline_node() after acpi_unmap_lsapic().

Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
---
 drivers/acpi/acpi_processor.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index fd6c51c..5a74a9c 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -451,7 +451,6 @@ static void acpi_processor_remove(struct acpi_device *device)
 	/* Clean up. */
 	per_cpu(processor_device_array, pr->id) = NULL;
 	per_cpu(processors, pr->id) = NULL;
-	try_offline_node(cpu_to_node(pr->id));

 	/* Remove the CPU. */
 	get_online_cpus();
@@ -459,6 +458,8 @@ static void acpi_processor_remove(struct acpi_device *device)
 	acpi_unmap_lsapic(pr->id);
 	put_online_cpus();

+	try_offline_node(cpu_to_node(pr->id));
+
  out:
 	free_cpumask_var(pr->throttling.shared_cpu_map);
 	kfree(pr);

Re: [PATCH] ACPI, cpu hotplug: move try_offline_node() after acpi_unmap_lsapic()

[Toshi Kani]

On Tue, 2013-08-06 at 19:11 +0900, Yasuaki Ishimatsu wrote:
> try_offline_node() checks that all cpus related with removed node have been
> removed by using cpu_present_bits. If all cpus related with removed node have
> been removed, try_offline_node() clears the node information.
> 
> But try_offline_node() called from acpi_processor_remove() never clears
> the node information. For disabling cpu_present_bits, acpi_unmap_lsapic()
> need be called. But acpi_unmap_lsapic() is called after try_offline_node()
> runs. So when try_offline_node() runs, the cpu's cpu_present_bits is always
> set.
> 
> This patch moves try_offline_node() after acpi_unmap_lsapic().
> 
> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>

The change looks good to me.

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

BTW, do you know why try_offline_node() has to use stop_machine()?

Thanks,
-Toshi

Re: [PATCH] ACPI, cpu hotplug: move try_offline_node() after acpi_unmap_lsapic()

[Yasuaki Ishimatsu]

(2013/08/07 1:56), Toshi Kani wrote:
> On Tue, 2013-08-06 at 19:11 +0900, Yasuaki Ishimatsu wrote:
>> try_offline_node() checks that all cpus related with removed node have been
>> removed by using cpu_present_bits. If all cpus related with removed node have
>> been removed, try_offline_node() clears the node information.
>>
>> But try_offline_node() called from acpi_processor_remove() never clears
>> the node information. For disabling cpu_present_bits, acpi_unmap_lsapic()
>> need be called. But acpi_unmap_lsapic() is called after try_offline_node()
>> runs. So when try_offline_node() runs, the cpu's cpu_present_bits is always
>> set.
>>
>> This patch moves try_offline_node() after acpi_unmap_lsapic().
>>
>> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
>
> The change looks good to me.
>
> Acked-by: Toshi Kani <toshi.kani@hp.com>

Thanks, Toshi!

> BTW, do you know why try_offline_node() has to use stop_machine()?

I don't know the reason.

Thanks,
Yasuaki Ishimatsu



>
> Thanks,
> -Toshi
>

Re: [PATCH] ACPI, cpu hotplug: move try_offline_node() after acpi_unmap_lsapic()

[Gu Zheng]

Hi Ishimatsu-san,
On 08/06/2013 06:11 PM, Yasuaki Ishimatsu wrote:

> try_offline_node() checks that all cpus related with removed node have been
> removed by using cpu_present_bits. If all cpus related with removed node have
> been removed, try_offline_node() clears the node information.
> 
> But try_offline_node() called from acpi_processor_remove() never clears
> the node information. For disabling cpu_present_bits, acpi_unmap_lsapic()
> need be called. But acpi_unmap_lsapic() is called after try_offline_node()
> runs. So when try_offline_node() runs, the cpu's cpu_present_bits is always
> set.
> 
> This patch moves try_offline_node() after acpi_unmap_lsapic().

It works well.

> 
> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>


Tested-by: Gu Zheng <guz.fnst@cn.fujitsu.com>

Thanks,
Gu

> ---
>  drivers/acpi/acpi_processor.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index fd6c51c..5a74a9c 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -451,7 +451,6 @@ static void acpi_processor_remove(struct acpi_device *device)
>  	/* Clean up. */
>  	per_cpu(processor_device_array, pr->id) = NULL;
>  	per_cpu(processors, pr->id) = NULL;
> -	try_offline_node(cpu_to_node(pr->id));
> 
>  	/* Remove the CPU. */
>  	get_online_cpus();
> @@ -459,6 +458,8 @@ static void acpi_processor_remove(struct acpi_device *device)
>  	acpi_unmap_lsapic(pr->id);
>  	put_online_cpus();
> 
> +	try_offline_node(cpu_to_node(pr->id));
> +
>   out:
>  	free_cpumask_var(pr->throttling.shared_cpu_map);
>  	kfree(pr);
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 

Re: [PATCH] ACPI, cpu hotplug: move try_offline_node() after acpi_unmap_lsapic()

[Yasuaki Ishimatsu]

(2013/08/09 11:43), Gu Zheng wrote:
> Hi Ishimatsu-san,
> On 08/06/2013 06:11 PM, Yasuaki Ishimatsu wrote:
> 
>> try_offline_node() checks that all cpus related with removed node have been
>> removed by using cpu_present_bits. If all cpus related with removed node have
>> been removed, try_offline_node() clears the node information.
>>
>> But try_offline_node() called from acpi_processor_remove() never clears
>> the node information. For disabling cpu_present_bits, acpi_unmap_lsapic()
>> need be called. But acpi_unmap_lsapic() is called after try_offline_node()
>> runs. So when try_offline_node() runs, the cpu's cpu_present_bits is always
>> set.
>>
>> This patch moves try_offline_node() after acpi_unmap_lsapic().
> 
> It works well.
> 
>>
>> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
> 
> 
> Tested-by: Gu Zheng <guz.fnst@cn.fujitsu.com>

Thank you for testing.

Thanks,
Yasuaki Ishimatsu

> 
> Thanks,
> Gu
> 
>> ---
>>   drivers/acpi/acpi_processor.c |    3 ++-
>>   1 files changed, 2 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
>> index fd6c51c..5a74a9c 100644
>> --- a/drivers/acpi/acpi_processor.c
>> +++ b/drivers/acpi/acpi_processor.c
>> @@ -451,7 +451,6 @@ static void acpi_processor_remove(struct acpi_device *device)
>>   	/* Clean up. */
>>   	per_cpu(processor_device_array, pr->id) = NULL;
>>   	per_cpu(processors, pr->id) = NULL;
>> -	try_offline_node(cpu_to_node(pr->id));
>>
>>   	/* Remove the CPU. */
>>   	get_online_cpus();
>> @@ -459,6 +458,8 @@ static void acpi_processor_remove(struct acpi_device *device)
>>   	acpi_unmap_lsapic(pr->id);
>>   	put_online_cpus();
>>
>> +	try_offline_node(cpu_to_node(pr->id));
>> +
>>    out:
>>   	free_cpumask_var(pr->throttling.shared_cpu_map);
>>   	kfree(pr);
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>> Please read the FAQ at  http://www.tux.org/lkml/
>>
> 
> 

Re: [PATCH] ACPI, cpu hotplug: move try_offline_node() after acpi_unmap_lsapic()

[Tang Chen]

On 08/07/2013 12:56 AM, Toshi Kani wrote:
> On Tue, 2013-08-06 at 19:11 +0900, Yasuaki Ishimatsu wrote:
>> try_offline_node() checks that all cpus related with removed node have been
>> removed by using cpu_present_bits. If all cpus related with removed node have
>> been removed, try_offline_node() clears the node information.
>>
>> But try_offline_node() called from acpi_processor_remove() never clears
>> the node information. For disabling cpu_present_bits, acpi_unmap_lsapic()
>> need be called. But acpi_unmap_lsapic() is called after try_offline_node()
>> runs. So when try_offline_node() runs, the cpu's cpu_present_bits is always
>> set.
>>
>> This patch moves try_offline_node() after acpi_unmap_lsapic().
>>
>> Signed-off-by: Yasuaki Ishimatsu<isimatu.yasuaki@jp.fujitsu.com>
>
> The change looks good to me.
>
> Acked-by: Toshi Kani<toshi.kani@hp.com>
>
> BTW, do you know why try_offline_node() has to use stop_machine()?

try_offline_node() is used to check if the node could be hot-removed
after each memory or cpu hot-remove operation.

In memory hot-remove path, we have lock_memory_hotplug() to series all
the memory hot-remove options.

But when doing cpu hot-remove,

acpi_processor_remove()
  |->try_offline_node()

There is no lock to protect it. I think, when we are going to hot-remove
a node, others should not do any memory or cpu hotplug operation. In memory
hotplug path, we have lock_memory_hotplug(). But in cpu hotplug path, I
didn't find any lock. So we used stop_machine() to call check_cpu_on_node().
If we find any cpu still present, we return and do not remove the node.

Thanks.

Re: [PATCH] ACPI, cpu hotplug: move try_offline_node() after acpi_unmap_lsapic()

[Toshi Kani]

On Fri, 2013-08-09 at 15:28 +0800, Tang Chen wrote:
> On 08/07/2013 12:56 AM, Toshi Kani wrote:
> > On Tue, 2013-08-06 at 19:11 +0900, Yasuaki Ishimatsu wrote:
> >> try_offline_node() checks that all cpus related with removed node have been
> >> removed by using cpu_present_bits. If all cpus related with removed node have
> >> been removed, try_offline_node() clears the node information.
> >>
> >> But try_offline_node() called from acpi_processor_remove() never clears
> >> the node information. For disabling cpu_present_bits, acpi_unmap_lsapic()
> >> need be called. But acpi_unmap_lsapic() is called after try_offline_node()
> >> runs. So when try_offline_node() runs, the cpu's cpu_present_bits is always
> >> set.
> >>
> >> This patch moves try_offline_node() after acpi_unmap_lsapic().
> >>
> >> Signed-off-by: Yasuaki Ishimatsu<isimatu.yasuaki@jp.fujitsu.com>
> >
> > The change looks good to me.
> >
> > Acked-by: Toshi Kani<toshi.kani@hp.com>
> >
> > BTW, do you know why try_offline_node() has to use stop_machine()?
> 
> try_offline_node() is used to check if the node could be hot-removed
> after each memory or cpu hot-remove operation.
> 
> In memory hot-remove path, we have lock_memory_hotplug() to series all
> the memory hot-remove options.
> 
> But when doing cpu hot-remove,
> 
> acpi_processor_remove()
>   |->try_offline_node()
> 
> There is no lock to protect it. I think, when we are going to hot-remove
> a node, others should not do any memory or cpu hotplug operation. In memory
> hotplug path, we have lock_memory_hotplug(). But in cpu hotplug path, I
> didn't find any lock. So we used stop_machine() to call check_cpu_on_node().
> If we find any cpu still present, we return and do not remove the node.

CPU/Memory hotplug operations and sysfs eject are serialized with
acpi_os_hotplug_execute().  CPU online/offline is protected by
cpu_hotplug_[begin|done]() and [get|put]_online_cpus().  But, yes,
online/offline and hotplug operations are not serialized.  I tried to
serialize them before, but that framework was not well received.

Anyway, it looks to me that cpu_up()->mem_online_node() path can race
with try_offline_node().  And I do not think stop_machine() protects
this case, either.  try_offline_node() stops the execution of
num_online_node() during stop_machine(), but then lets it continues to
run after that.  I think they need to be protected by a lock.

I will look further to see if I can come up with some solution.

Thanks,
-Toshi

Re: [PATCH] ACPI, cpu hotplug: move try_offline_node() after acpi_unmap_lsapic()

[Rafael J. Wysocki]

On Friday, August 09, 2013 04:16:56 PM Toshi Kani wrote:
> On Fri, 2013-08-09 at 15:28 +0800, Tang Chen wrote:
> > On 08/07/2013 12:56 AM, Toshi Kani wrote:
> > > On Tue, 2013-08-06 at 19:11 +0900, Yasuaki Ishimatsu wrote:
> > >> try_offline_node() checks that all cpus related with removed node have been
> > >> removed by using cpu_present_bits. If all cpus related with removed node have
> > >> been removed, try_offline_node() clears the node information.
> > >>
> > >> But try_offline_node() called from acpi_processor_remove() never clears
> > >> the node information. For disabling cpu_present_bits, acpi_unmap_lsapic()
> > >> need be called. But acpi_unmap_lsapic() is called after try_offline_node()
> > >> runs. So when try_offline_node() runs, the cpu's cpu_present_bits is always
> > >> set.
> > >>
> > >> This patch moves try_offline_node() after acpi_unmap_lsapic().
> > >>
> > >> Signed-off-by: Yasuaki Ishimatsu<isimatu.yasuaki@jp.fujitsu.com>
> > >
> > > The change looks good to me.
> > >
> > > Acked-by: Toshi Kani<toshi.kani@hp.com>
> > >
> > > BTW, do you know why try_offline_node() has to use stop_machine()?
> > 
> > try_offline_node() is used to check if the node could be hot-removed
> > after each memory or cpu hot-remove operation.
> > 
> > In memory hot-remove path, we have lock_memory_hotplug() to series all
> > the memory hot-remove options.
> > 
> > But when doing cpu hot-remove,
> > 
> > acpi_processor_remove()
> >   |->try_offline_node()
> > 
> > There is no lock to protect it. I think, when we are going to hot-remove
> > a node, others should not do any memory or cpu hotplug operation. In memory
> > hotplug path, we have lock_memory_hotplug(). But in cpu hotplug path, I
> > didn't find any lock. So we used stop_machine() to call check_cpu_on_node().
> > If we find any cpu still present, we return and do not remove the node.
> 
> CPU/Memory hotplug operations and sysfs eject are serialized with
> acpi_os_hotplug_execute().  CPU online/offline is protected by
> cpu_hotplug_[begin|done]() and [get|put]_online_cpus().  But, yes,
> online/offline and hotplug operations are not serialized.  I tried to
> serialize them before, but that framework was not well received.

What about lock_device_hotplug()?  It is taken by both online/offline and
the ACPI hotplug code, isn't it?

> Anyway, it looks to me that cpu_up()->mem_online_node() path can race
> with try_offline_node().

It can in principle, but I'm not sure if there's a way to trigger that
race.  Do you have an example?

Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

Re: [PATCH] ACPI, cpu hotplug: move try_offline_node() after acpi_unmap_lsapic()

[Toshi Kani]

On Sat, 2013-08-10 at 01:29 +0200, Rafael J. Wysocki wrote:
> On Friday, August 09, 2013 04:16:56 PM Toshi Kani wrote:
> > On Fri, 2013-08-09 at 15:28 +0800, Tang Chen wrote:
> > > On 08/07/2013 12:56 AM, Toshi Kani wrote:
> > > > On Tue, 2013-08-06 at 19:11 +0900, Yasuaki Ishimatsu wrote:
> > > >> try_offline_node() checks that all cpus related with removed node have been
> > > >> removed by using cpu_present_bits. If all cpus related with removed node have
> > > >> been removed, try_offline_node() clears the node information.
> > > >>
> > > >> But try_offline_node() called from acpi_processor_remove() never clears
> > > >> the node information. For disabling cpu_present_bits, acpi_unmap_lsapic()
> > > >> need be called. But acpi_unmap_lsapic() is called after try_offline_node()
> > > >> runs. So when try_offline_node() runs, the cpu's cpu_present_bits is always
> > > >> set.
> > > >>
> > > >> This patch moves try_offline_node() after acpi_unmap_lsapic().
> > > >>
> > > >> Signed-off-by: Yasuaki Ishimatsu<isimatu.yasuaki@jp.fujitsu.com>
> > > >
> > > > The change looks good to me.
> > > >
> > > > Acked-by: Toshi Kani<toshi.kani@hp.com>
> > > >
> > > > BTW, do you know why try_offline_node() has to use stop_machine()?
> > > 
> > > try_offline_node() is used to check if the node could be hot-removed
> > > after each memory or cpu hot-remove operation.
> > > 
> > > In memory hot-remove path, we have lock_memory_hotplug() to series all
> > > the memory hot-remove options.
> > > 
> > > But when doing cpu hot-remove,
> > > 
> > > acpi_processor_remove()
> > >   |->try_offline_node()
> > > 
> > > There is no lock to protect it. I think, when we are going to hot-remove
> > > a node, others should not do any memory or cpu hotplug operation. In memory
> > > hotplug path, we have lock_memory_hotplug(). But in cpu hotplug path, I
> > > didn't find any lock. So we used stop_machine() to call check_cpu_on_node().
> > > If we find any cpu still present, we return and do not remove the node.
> > 
> > CPU/Memory hotplug operations and sysfs eject are serialized with
> > acpi_os_hotplug_execute().  CPU online/offline is protected by
> > cpu_hotplug_[begin|done]() and [get|put]_online_cpus().  But, yes,
> > online/offline and hotplug operations are not serialized.  I tried to
> > serialize them before, but that framework was not well received.
> 
> What about lock_device_hotplug()?  It is taken by both online/offline and
> the ACPI hotplug code, isn't it?

Oh, that's right!  I forgot about this one.  Yes, lock_device_hotplug()
nicely protects online/offline and hotplug operations. :-)

> > Anyway, it looks to me that cpu_up()->mem_online_node() path can race
> > with try_offline_node().
> 
> It can in principle, but I'm not sure if there's a way to trigger that
> race.  Do you have an example?

With lock_device_hotplug(), I agree that we do not have this race
condition -- cpu_up() may not run while other hotplug is running.
store_online() will be blocked at lock_device_hotplug() in such case.
When store_online() acquired the lock, this CPU may have been deleted.
So, we still need to make sure that this case is handled properly.  I
suppose sysfs keeps *dev valid with ref_count (Is that right?).  I think
cpu_up() needs to check with cpu_present(), not cpu_possible(), at the
top.  Otherwise, cpu_to_node(cpu) may return NUMA_NO_NODE (-1), which is
probably not a good value for node_online(nid).

Thanks,
-Toshi

Re: [PATCH] ACPI, cpu hotplug: move try_offline_node() after acpi_unmap_lsapic()

[Rafael J. Wysocki]

On Friday, August 09, 2013 08:11:19 PM Toshi Kani wrote:
> On Sat, 2013-08-10 at 01:29 +0200, Rafael J. Wysocki wrote:
> > On Friday, August 09, 2013 04:16:56 PM Toshi Kani wrote:
> > > On Fri, 2013-08-09 at 15:28 +0800, Tang Chen wrote:
> > > > On 08/07/2013 12:56 AM, Toshi Kani wrote:
> > > > > On Tue, 2013-08-06 at 19:11 +0900, Yasuaki Ishimatsu wrote:
> > > > >> try_offline_node() checks that all cpus related with removed node have been
> > > > >> removed by using cpu_present_bits. If all cpus related with removed node have
> > > > >> been removed, try_offline_node() clears the node information.
> > > > >>
> > > > >> But try_offline_node() called from acpi_processor_remove() never clears
> > > > >> the node information. For disabling cpu_present_bits, acpi_unmap_lsapic()
> > > > >> need be called. But acpi_unmap_lsapic() is called after try_offline_node()
> > > > >> runs. So when try_offline_node() runs, the cpu's cpu_present_bits is always
> > > > >> set.
> > > > >>
> > > > >> This patch moves try_offline_node() after acpi_unmap_lsapic().
> > > > >>
> > > > >> Signed-off-by: Yasuaki Ishimatsu<isimatu.yasuaki@jp.fujitsu.com>
> > > > >
> > > > > The change looks good to me.
> > > > >
> > > > > Acked-by: Toshi Kani<toshi.kani@hp.com>
> > > > >
> > > > > BTW, do you know why try_offline_node() has to use stop_machine()?
> > > > 
> > > > try_offline_node() is used to check if the node could be hot-removed
> > > > after each memory or cpu hot-remove operation.
> > > > 
> > > > In memory hot-remove path, we have lock_memory_hotplug() to series all
> > > > the memory hot-remove options.
> > > > 
> > > > But when doing cpu hot-remove,
> > > > 
> > > > acpi_processor_remove()
> > > >   |->try_offline_node()
> > > > 
> > > > There is no lock to protect it. I think, when we are going to hot-remove
> > > > a node, others should not do any memory or cpu hotplug operation. In memory
> > > > hotplug path, we have lock_memory_hotplug(). But in cpu hotplug path, I
> > > > didn't find any lock. So we used stop_machine() to call check_cpu_on_node().
> > > > If we find any cpu still present, we return and do not remove the node.
> > > 
> > > CPU/Memory hotplug operations and sysfs eject are serialized with
> > > acpi_os_hotplug_execute().  CPU online/offline is protected by
> > > cpu_hotplug_[begin|done]() and [get|put]_online_cpus().  But, yes,
> > > online/offline and hotplug operations are not serialized.  I tried to
> > > serialize them before, but that framework was not well received.
> > 
> > What about lock_device_hotplug()?  It is taken by both online/offline and
> > the ACPI hotplug code, isn't it?
> 
> Oh, that's right!  I forgot about this one.  Yes, lock_device_hotplug()
> nicely protects online/offline and hotplug operations. :-)
> 
> > > Anyway, it looks to me that cpu_up()->mem_online_node() path can race
> > > with try_offline_node().
> > 
> > It can in principle, but I'm not sure if there's a way to trigger that
> > race.  Do you have an example?
> 
> With lock_device_hotplug(), I agree that we do not have this race
> condition -- cpu_up() may not run while other hotplug is running.
> store_online() will be blocked at lock_device_hotplug() in such case.
> When store_online() acquired the lock, this CPU may have been deleted.
> So, we still need to make sure that this case is handled properly.

Yes.

> I suppose sysfs keeps *dev valid with ref_count (Is that right?).

Yes, it does.

> I think cpu_up() needs to check with cpu_present(), not cpu_possible(), at
> the top.  Otherwise, cpu_to_node(cpu) may return NUMA_NO_NODE (-1), which is
> probably not a good value for node_online(nid).

We do cpu_to_node(cpuid) in cpu_subsys_online() before that, so maybe
it's better to check the result already there and bail out if that's
negative?

Something like the patch below.

Thanks,
Rafael


---
 drivers/base/cpu.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Index: linux-pm/drivers/base/cpu.c
===================================================================
--- linux-pm.orig/drivers/base/cpu.c
+++ linux-pm/drivers/base/cpu.c
@@ -43,11 +43,14 @@ static int __ref cpu_subsys_online(struc
 	struct cpu *cpu = container_of(dev, struct cpu, dev);
 	int cpuid = dev->id;
 	int from_nid, to_nid;
-	int ret;
+	int ret = -ENODEV;
 
 	cpu_hotplug_driver_lock();
 
 	from_nid = cpu_to_node(cpuid);
+	if (from_nid == NUMA_NO_NODE)
+		goto out;
+
 	ret = cpu_up(cpuid);
 	/*
 	 * When hot adding memory to memoryless node and enabling a cpu
@@ -57,6 +60,7 @@ static int __ref cpu_subsys_online(struc
 	if (from_nid != to_nid)
 		change_cpu_under_node(cpu, from_nid, to_nid);
 
+ out:
 	cpu_hotplug_driver_unlock();
 	return ret;
 }

Re: [PATCH] ACPI, cpu hotplug: move try_offline_node() after acpi_unmap_lsapic()

[Toshi Kani]

On Sun, 2013-08-11 at 22:42 +0200, Rafael J. Wysocki wrote:
> On Friday, August 09, 2013 08:11:19 PM Toshi Kani wrote:
> > On Sat, 2013-08-10 at 01:29 +0200, Rafael J. Wysocki wrote:
> > > On Friday, August 09, 2013 04:16:56 PM Toshi Kani wrote:
> > > > On Fri, 2013-08-09 at 15:28 +0800, Tang Chen wrote:
> > > > > On 08/07/2013 12:56 AM, Toshi Kani wrote:
 :
> > > > > > BTW, do you know why try_offline_node() has to use stop_machine()?
> > > > > 
> > > > > try_offline_node() is used to check if the node could be hot-removed
> > > > > after each memory or cpu hot-remove operation.
> > > > > 
> > > > > In memory hot-remove path, we have lock_memory_hotplug() to series all
> > > > > the memory hot-remove options.
> > > > > 
> > > > > But when doing cpu hot-remove,
> > > > > 
> > > > > acpi_processor_remove()
> > > > >   |->try_offline_node()
> > > > > 
> > > > > There is no lock to protect it. I think, when we are going to hot-remove
> > > > > a node, others should not do any memory or cpu hotplug operation. In memory
> > > > > hotplug path, we have lock_memory_hotplug(). But in cpu hotplug path, I
> > > > > didn't find any lock. So we used stop_machine() to call check_cpu_on_node().
> > > > > If we find any cpu still present, we return and do not remove the node.
> > > > 
> > > > CPU/Memory hotplug operations and sysfs eject are serialized with
> > > > acpi_os_hotplug_execute().  CPU online/offline is protected by
> > > > cpu_hotplug_[begin|done]() and [get|put]_online_cpus().  But, yes,
> > > > online/offline and hotplug operations are not serialized.  I tried to
> > > > serialize them before, but that framework was not well received.
> > > 
> > > What about lock_device_hotplug()?  It is taken by both online/offline and
> > > the ACPI hotplug code, isn't it?
> > 
> > Oh, that's right!  I forgot about this one.  Yes, lock_device_hotplug()
> > nicely protects online/offline and hotplug operations. :-)
> > 
> > > > Anyway, it looks to me that cpu_up()->mem_online_node() path can race
> > > > with try_offline_node().
> > > 
> > > It can in principle, but I'm not sure if there's a way to trigger that
> > > race.  Do you have an example?
> > 
> > With lock_device_hotplug(), I agree that we do not have this race
> > condition -- cpu_up() may not run while other hotplug is running.
> > store_online() will be blocked at lock_device_hotplug() in such case.
> > When store_online() acquired the lock, this CPU may have been deleted.
> > So, we still need to make sure that this case is handled properly.
> 
> Yes.
> 
> > I suppose sysfs keeps *dev valid with ref_count (Is that right?).
> 
> Yes, it does.
> 
> > I think cpu_up() needs to check with cpu_present(), not cpu_possible(), at
> > the top.  Otherwise, cpu_to_node(cpu) may return NUMA_NO_NODE (-1), which is
> > probably not a good value for node_online(nid).
> 
> We do cpu_to_node(cpuid) in cpu_subsys_online() before that, so maybe
> it's better to check the result already there and bail out if that's
> negative?
> 
> Something like the patch below.

That looks good to me.

Thanks,
-Toshi

Re: [PATCH] driver core / cpu: Check if NUMA node is valid before bringing CPU up

[Toshi Kani]

On Tue, 2013-08-13 at 02:39 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> There is a potential race condition between cpu_subsys_online()
> and either acpi_processor_remove() or remove_memory() that execute
> try_offline_node().  Namely, it is possible that cpu_subsys_online()
> will run right after the CPUs NUMA node has been put offline and
> cpu_to_node() executed by it will return NUMA_NO_NODE (-1).  In
> that case the CPU is gone and it doesn't make sense to call cpu_up()
> for it, so make cpu_subsys_online() return -ENODEV then.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Acked-by: Toshi Kani <toshi.kani@hp.com>
> ---
> 
> Hi Greg,
> 
> Can you please kindly queue up this one for 3.12?
> 
> I've added the Toshi's ACK as he said it looked good to him. :-)

That's fine by me.
-Toshi

[PATCH] driver core / cpu: Check if NUMA node is valid before bringing CPU up

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

There is a potential race condition between cpu_subsys_online()
and either acpi_processor_remove() or remove_memory() that execute
try_offline_node().  Namely, it is possible that cpu_subsys_online()
will run right after the CPUs NUMA node has been put offline and
cpu_to_node() executed by it will return NUMA_NO_NODE (-1).  In
that case the CPU is gone and it doesn't make sense to call cpu_up()
for it, so make cpu_subsys_online() return -ENODEV then.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Toshi Kani <toshi.kani@hp.com>
---

Hi Greg,

Can you please kindly queue up this one for 3.12?

I've added the Toshi's ACK as he said it looked good to him. :-)

Thanks,
Rafael

---
 drivers/base/cpu.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Index: linux-pm/drivers/base/cpu.c
===================================================================
--- linux-pm.orig/drivers/base/cpu.c
+++ linux-pm/drivers/base/cpu.c
@@ -43,11 +43,14 @@ static int __ref cpu_subsys_online(struc
 	struct cpu *cpu = container_of(dev, struct cpu, dev);
 	int cpuid = dev->id;
 	int from_nid, to_nid;
-	int ret;
+	int ret = -ENODEV;
 
 	cpu_hotplug_driver_lock();
 
 	from_nid = cpu_to_node(cpuid);
+	if (from_nid == NUMA_NO_NODE)
+		goto out;
+
 	ret = cpu_up(cpuid);
 	/*
 	 * When hot adding memory to memoryless node and enabling a cpu
@@ -57,6 +60,7 @@ static int __ref cpu_subsys_online(struc
 	if (from_nid != to_nid)
 		change_cpu_under_node(cpu, from_nid, to_nid);
 
+ out:
 	cpu_hotplug_driver_unlock();
 	return ret;
 }