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

James Bottomley
2014-05-02T14:48:42Z

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

James