[PATCH] mm: add restriction when memory_hotplug config enable

[PATCH] mm: add restriction when memory_hotplug config enable

[zhongjiang]

From: zhong jiang <zhongjiang@huawei.com>

At present, It is obvious that memory online and offline will fail
when KASAN enable,  therefore, it is necessary to add the condition
to limit the memory_hotplug when KASAN enable.

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
---
 mm/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/Kconfig b/mm/Kconfig
index 3e2daef..f6dd77e 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -187,6 +187,7 @@ config MEMORY_HOTPLUG
 	bool "Allow for memory hot-add"
 	depends on SPARSEMEM || X86_64_ACPI_NUMA
 	depends on ARCH_ENABLE_MEMORY_HOTPLUG
+	depends on !KASAN
 
 config MEMORY_HOTPLUG_SPARSE
 	def_bool y
-- 
1.8.3.1

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Re: [PATCH] mm: add restriction when memory_hotplug config enable

[Andrew Morton]

On Mon, 1 Aug 2016 23:00:51 +0800 zhongjiang <zhongjiang@huawei.com> wrote:

> From: zhong jiang <zhongjiang@huawei.com>
> 
> At present, It is obvious that memory online and offline will fail
> when KASAN enable,

huh, I didn't know that.  What's the problem and are there plans to fix it?

>  therefore, it is necessary to add the condition
> to limit the memory_hotplug when KASAN enable.
> 
> Signed-off-by: zhong jiang <zhongjiang@huawei.com>
> ---
>  mm/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 3e2daef..f6dd77e 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -187,6 +187,7 @@ config MEMORY_HOTPLUG
>  	bool "Allow for memory hot-add"
>  	depends on SPARSEMEM || X86_64_ACPI_NUMA
>  	depends on ARCH_ENABLE_MEMORY_HOTPLUG
> +	depends on !KASAN
>  
>  config MEMORY_HOTPLUG_SPARSE
>  	def_bool y

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Re: [PATCH] mm: add restriction when memory_hotplug config enable

[zhong jiang]

On 2016/8/2 3:54, Andrew Morton wrote:
> On Mon, 1 Aug 2016 23:00:51 +0800 zhongjiang <zhongjiang@huawei.com> wrote:
>
>> From: zhong jiang <zhongjiang@huawei.com>
>>
>> At present, It is obvious that memory online and offline will fail
>> when KASAN enable,
> huh, I didn't know that.  What's the problem and are there plans to fix it?
   when I  test the memory hotplug function.  The memory online and offline always fails.
   because I forget the turn off  the KASAN config.  I know it is not compatible with hotplug.
   In fact,  but I always forget to do so.  
>>  therefore, it is necessary to add the condition
>> to limit the memory_hotplug when KASAN enable.
>>
>> Signed-off-by: zhong jiang <zhongjiang@huawei.com>
>> ---
>>  mm/Kconfig | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index 3e2daef..f6dd77e 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -187,6 +187,7 @@ config MEMORY_HOTPLUG
>>  	bool "Allow for memory hot-add"
>>  	depends on SPARSEMEM || X86_64_ACPI_NUMA
>>  	depends on ARCH_ENABLE_MEMORY_HOTPLUG
>> +	depends on !KASAN
>>  
>>  config MEMORY_HOTPLUG_SPARSE
>>  	def_bool y
> --
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>


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Re: [PATCH] mm: add restriction when memory_hotplug config enable

[Andrey Ryabinin]

On 08/01/2016 10:54 PM, Andrew Morton wrote:
> On Mon, 1 Aug 2016 23:00:51 +0800 zhongjiang <zhongjiang@huawei.com> wrote:
> 
>> From: zhong jiang <zhongjiang@huawei.com>
>>
>> At present, It is obvious that memory online and offline will fail
>> when KASAN enable,
> 
> huh, I didn't know that.

Ahem... https://lkml.kernel.org/r/<20150130133552.580f73b97a9bd007979b5419@linux-foundation.org>

Also

commit 786a8959912eb94fc2381c2ae487a96ce55dabca
    kasan: disable memory hotplug
    
    Currently memory hotplug won't work with KASan.  As we don't have shadow
    for hotplugged memory, kernel will crash on the first access to it.  To
    make this work we will need to allocate shadow for new memory.
    
    At some future point proper memory hotplug support will be implemented.
    Until then, print a warning at startup and disable memory hot-add.



> What's the problem and are there plans to fix it?

Nobody complained, so I didn't bother to fix it.
The fix for this should be simple, I'll look into this.

> 
>>  therefore, it is necessary to add the condition
>> to limit the memory_hotplug when KASAN enable.
>>

I don't understand why we need Kconfig dependency.
Why is that better than runtime warn message?

>> Signed-off-by: zhong jiang <zhongjiang@huawei.com>
>> ---
>>  mm/Kconfig | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index 3e2daef..f6dd77e 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -187,6 +187,7 @@ config MEMORY_HOTPLUG
>>  	bool "Allow for memory hot-add"
>>  	depends on SPARSEMEM || X86_64_ACPI_NUMA
>>  	depends on ARCH_ENABLE_MEMORY_HOTPLUG
>> +	depends on !KASAN
>>  
>>  config MEMORY_HOTPLUG_SPARSE
>>  	def_bool y
> 

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Re: [PATCH] mm: add restriction when memory_hotplug config enable

[zhong jiang]

On 2016/8/2 18:40, Andrey Ryabinin wrote:
>
> On 08/01/2016 10:54 PM, Andrew Morton wrote:
>> On Mon, 1 Aug 2016 23:00:51 +0800 zhongjiang <zhongjiang@huawei.com> wrote:
>>
>>> From: zhong jiang <zhongjiang@huawei.com>
>>>
>>> At present, It is obvious that memory online and offline will fail
>>> when KASAN enable,
>> huh, I didn't know that.
> Ahem... https://lkml.kernel.org/r/<20150130133552.580f73b97a9bd007979b5419@linux-foundation.org>
>
> Also
>
> commit 786a8959912eb94fc2381c2ae487a96ce55dabca
>     kasan: disable memory hotplug
>     
>     Currently memory hotplug won't work with KASan.  As we don't have shadow
>     for hotplugged memory, kernel will crash on the first access to it.  To
>     make this work we will need to allocate shadow for new memory.
>     
>     At some future point proper memory hotplug support will be implemented.
>     Until then, print a warning at startup and disable memory hot-add.
>
>
>
>> What's the problem and are there plans to fix it?
> Nobody complained, so I didn't bother to fix it.
> The fix for this should be simple, I'll look into this.
>
>>>  therefore, it is necessary to add the condition
>>> to limit the memory_hotplug when KASAN enable.
>>>
> I don't understand why we need Kconfig dependency.
> Why is that better than runtime warn message?
  The user rarely care about the runtime warn message when the
  system is good running.  In fact, They are confilct with each other.
  For me,  I know the reason. but I always forget to do so. As a result,
  I test the memory hotplug fails again.  so, I hope to add the explicit dependency.
 
  Thanks
  zhongjiang
>>> Signed-off-by: zhong jiang <zhongjiang@huawei.com>
>>> ---
>>>  mm/Kconfig | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/mm/Kconfig b/mm/Kconfig
>>> index 3e2daef..f6dd77e 100644
>>> --- a/mm/Kconfig
>>> +++ b/mm/Kconfig
>>> @@ -187,6 +187,7 @@ config MEMORY_HOTPLUG
>>>  	bool "Allow for memory hot-add"
>>>  	depends on SPARSEMEM || X86_64_ACPI_NUMA
>>>  	depends on ARCH_ENABLE_MEMORY_HOTPLUG
>>> +	depends on !KASAN
>>>  
>>>  config MEMORY_HOTPLUG_SPARSE
>>>  	def_bool y
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>


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Re: [PATCH] mm: add restriction when memory_hotplug config enable

[Andrew Morton]

On Wed, 3 Aug 2016 13:53:10 +0800 zhong jiang <zhongjiang@huawei.com> wrote:

> On 2016/8/2 18:40, Andrey Ryabinin wrote:
> >
> > On 08/01/2016 10:54 PM, Andrew Morton wrote:
> >> On Mon, 1 Aug 2016 23:00:51 +0800 zhongjiang <zhongjiang@huawei.com> wrote:
> >>
> >>> From: zhong jiang <zhongjiang@huawei.com>
> >>>
> >>> At present, It is obvious that memory online and offline will fail
> >>> when KASAN enable,
> >> huh, I didn't know that.
> > Ahem... https://lkml.kernel.org/r/<20150130133552.580f73b97a9bd007979b5419@linux-foundation.org>
> >
> > Also
> >
> > commit 786a8959912eb94fc2381c2ae487a96ce55dabca
> >     kasan: disable memory hotplug
> >     
> >     Currently memory hotplug won't work with KASan.  As we don't have shadow
> >     for hotplugged memory, kernel will crash on the first access to it.  To
> >     make this work we will need to allocate shadow for new memory.
> >     
> >     At some future point proper memory hotplug support will be implemented.
> >     Until then, print a warning at startup and disable memory hot-add.
> >
> >
> >
> >> What's the problem and are there plans to fix it?
> > Nobody complained, so I didn't bother to fix it.
> > The fix for this should be simple, I'll look into this.
> >
> >>>  therefore, it is necessary to add the condition
> >>> to limit the memory_hotplug when KASAN enable.
> >>>
> > I don't understand why we need Kconfig dependency.
> > Why is that better than runtime warn message?
>   The user rarely care about the runtime warn message when the
>   system is good running.  In fact, They are confilct with each other.
>   For me,  I know the reason. but I always forget to do so. As a result,
>   I test the memory hotplug fails again.  so, I hope to add the explicit dependency.

Yes, I think it's better to disable the configuration than to permit
people to run known-to-be-broken kernel setups - that will just cause
confusion and pointless bug reports.  Let's undo the Kconfig change
when this gets fixed up.


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