[parisc-linux] [PATCH] fix arbitrary limits on stack size

[Joel Soete]

>One of the problems with the PA linux implementation is the upward
>growing stack.  On most architectures, the virtual process space is
>divided into
>
>
>| unmapped | exec and heap |  mappings and stack | TASK_UNMAPPED_BASE  
     
>TASK_SIZE
>
>
>The mappings grow up from the start and the stack grows down from the
>end of the area. If they ever meet, the process segfaults.
>
>On palinux, we have an upward growing stack, so we have to size the
>stack so when it reaches its ulimit, it hits the top of the area.  This
>means that large stack limits cut into the mappable area (and also that
>we have to impose a hard limit of 1GB on the stack size otherwise the
>user could remove the ability to map processes entirely by setting the
>stack limit too high).
>
>The proposal to fix this is to start the stack growing upwards from
>TASK_UNMAPPED_BASE and have the mappings grow downwards from TASK_SIZE.

>This should allow us to behave in exactly the same manner as x86 and not
>have an arbitrary limit on the stack size.
>
>The attached patch (against 2.5.70-pa1) does this, if you'd like to
>comment on it or try it out.

I don' t remember the historical reason of this choice but do you think it
is possible to back-port it into 2.4 (it will facilitate so much the merge
with upstream?)

Thanks in advance for advise,
    Joel

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