Request for review: 6978641 ( was Re: Request for approval: 6929067: Stack guard pages should be removed when thread is detached)

[David Holmes]

John Coomes said the following on 08/24/10 07:10:
> David Holmes (David.Holmes at oracle.com) wrote:
>> Here's the official OpenJKDK webrev for this:
>>
>> http://cr.openjdk.java.net/~dholmes/6978641/
> 
> Hi David,
> 
> Looks good to me, aside from one syntax nit:  I find it hard to read
> when control flow is embedded in macros like DEBUG_ONLY(),
> PRODUCT_ONLY(), etc.  Using a separate variable is easier to read and
> also can be useful in the debugger, e.g.,
> 
>    bool chk_bounds = NOT_DEBUG(os::Linux::is_initial_thread()) DEBUG_ONLY(true);
>    if (chk_bounds && get_stack_bounds(&stack_extent, &stack_base)) {
>      assert(...);

Thanks John, I've implemented your suggestion - webrev updated.

David

> -John
> 
>> If I can add you both as reviewers that would be great.
>>
>> Coleen can you send me details on which release/build I should use in 
>> the CR and also if there is any special "magic" I need to submit via JPRT.
>>
>> Thanks,
>> David
>>
>> Coleen Phillimore said the following on 08/20/10 23:15:
>>> This change looks fine to me and yes, thanks for pointing out that I did 
>>> add the test.
>>>
>>> Coleen
>>>
>>> Andrew Haley wrote:
>>>> 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?
>>>>
>>>>  
>>>>> @@ -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.
>>>>   
>