Request for approval: 6929067: Stack guard pages should be removed when thread is detached

[David Holmes]

Andrew Haley said the following on 08/20/10 18:34:
> On 08/19/2010 04:49 AM, David Holmes wrote:
> 
>> diff -r f707b4c0c36f src/os/linux/vm/os_linux.cpp
>> --- a/src/os/linux/vm/os_linux.cpp
>> +++ b/src/os/linux/vm/os_linux.cpp
>> @@ -2628,10 +2628,12 @@ get_stack_bounds(uintptr_t *bottom, uint
>>  // where we're going to put our guard pages, truncate the mapping at
>>  // that point by munmap()ping it.  This ensures that when we later
>>  // munmap() the guard pages we don't leave a hole in the stack
>> -// mapping.
>> +// mapping. This only affects the main/initial thread, but guard
>> +// against future OS changes
>>  bool os::create_stack_guard_pages(char* addr, size_t size) {
>>    uintptr_t stack_extent, stack_base;
>> -  if (get_stack_bounds(&stack_extent, &stack_base)) {
>> +  if (NOT_DEBUG(os::Linux::is_initial_thread() &&) get_stack_bounds(&stack_extent, &stack_base)) {
>> +      assert(os::Linux::is_initial_thread(), "growable stack in non-initial thread");
>>      if (stack_extent < (uintptr_t)addr)
>>        ::munmap((void*)stack_extent, (uintptr_t)addr - stack_extent);
>>    }
> 
> Is stack_extent initialized here in NOT_DEBUG mode?

It may not be, but in that case it is unused.

I filed 6978641 for this and will request a formal review shortly.

Thanks,
David

>> @@ -2640,10 +2642,13 @@ bool os::create_stack_guard_pages(char*
>>  }
>>
>>  // If this is a growable mapping, remove the guard pages entirely by
>> -// munmap()ping them.  If not, just call uncommit_memory().
>> +// munmap()ping them.  If not, just call uncommit_memory(). This only
>> +// affects the main/initial thread, but guard against future OS changes
>>  bool os::remove_stack_guard_pages(char* addr, size_t size) {
>>    uintptr_t stack_extent, stack_base;
>> -  if (get_stack_bounds(&stack_extent, &stack_base)) {
>> +  if (NOT_DEBUG(os::Linux::is_initial_thread() &&) get_stack_bounds(&stack_extent, &stack_base)) {
>> +      assert(os::Linux::is_initial_thread(), "growable stack in non-initial thread");
>> +
>>      return ::munmap(addr, size) == 0;
>>    } 
> 
> This is basically a good compromise, I think.
> 
> Andrew.