Re: [PATCH] parisc,metag: Do not hardcode maximum userspace stack size

Helge Deller
2014-05-04T07:28:05Z

On 05/02/2014 04:48 PM, James Bottomley wrote:
> On Fri, 2014-05-02 at 12:54 +0100, James Hogan wrote:
>> On 01/05/14 18:50, James Bottomley wrote:
>>>
>>>> +
>>>> +config MAX_STACK_SIZE_MB
>>>> + int "Maximum user stack size (MB)"
>>>> + default 80
>>>> + range 8 256 if METAG
>>>> + range 8 2048
>>>> + depends on STACK_GROWSUP
>>>> + help
>>>> + This is the maximum stack size in Megabytes in the VM layout of user
>>>> + processes when the stack grows upwards (currently only on parisc and
>>>> + metag arch). The stack will be located at the highest memory address
>>>> + minus the given value, unless the RLIMIT_STACK hard limit is changed
>>>> + to a smaller value in which case that is used.
>>>> +
>>>> + A sane initial value is 80 MB.
>>>
>>> There's one final issue with this: placement of the stack only really
>>> matters on 32 bits. We have three expanding memory areas: stack, heap
>>> and maps. On 64 bits these are placed well separated from each other on
>>> 64 bits, so an artificial limit like this doesn't matter.
>>
>> Does the following fixup diff look reasonable? It forces
>> MAX_STACK_SIZE_MB to 1024 and hides the Kconfig option for 64BIT,
>> effectively leaving the behaviour unchanged in that case.
>>
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index e80075979530..b0307f737bd7 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -583,7 +583,8 @@ config GENERIC_EARLY_IOREMAP
>> bool
>>
>> config MAX_STACK_SIZE_MB
>> - int "Maximum user stack size (MB)"
>> + int "Maximum user stack size (MB)" if !64BIT
>> + default 1024 if 64BIT
>> default 80
>> range 8 256 if METAG
>> range 8 2048
>
> Yes, I think that's probably correct ...

No, it's not correct.
It will then choose then a 1GB stack for compat tasks on 64bit kernel.

Helge

> parisc doesn't actually have
> anything other than a testbed 64 bit userspace, so this is a bit
> theoretical for us.

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