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

[John Coomes]

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(...);

-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.
> >>