RFR(XS)(10): 8175342: assert(InstanceKlass::cast(k)->is_initialized()) failed: need to increase java_thread_min_stack_allowed calculation

[Chris Plummer]

I should have been more clear. I need one more "reviewer", not another 
review from David.

thanks,

Chris

On 3/17/17 12:30 AM, Chris Plummer wrote:
> Thanks for the review, David.
>
> I could still use one more review. Here's an updated webrev.
>
> http://cr.openjdk.java.net/~cjplummer/8175342/webrev.01/webrev.jdk
>
> cheers,
>
> Chris
>
> On 3/15/17 10:14 PM, David Holmes wrote:
>> Hi Chris,
>>
>> On 16/03/2017 2:57 PM, Chris Plummer wrote:
>>> Hello,
>>>
>>> Please review the following:
>>>
>>> https://bugs.openjdk.java.net/browse/JDK-8175342
>>> http://cr.openjdk.java.net/~cjplummer/8175342/webrev.00/webrev.jdk
>>
>> I think you want to disable the guardpage always, not just when a 
>> specific stack size is requested. You might not miss 64KB in 8MB but 
>> logically the guard page is never needed.
>>
>> Thanks,
>> David
>> -----
>>
>>> The assert is somewhat misleading, although it did properly detect a
>>> "too small" stack issue. The test was run with -Xss256k on a system 
>>> with
>>> 64k pages. On this system 256k is suppose to be the smallest allowed
>>> stack size, so -Xss256k should work. The thread that the assert happens
>>> on is the main thread created by ContinueInNewThread0(). By default
>>> pthread gives new threads a guard page the size of an OS page. pthreads
>>> is suppose to add additional stack space for the guard page, but it
>>> doesn't. Later we call current_stack_region(), which among other 
>>> things,
>>> computes the size of the stack. It has the following code to deal with
>>> the pthread guard page bug:
>>>
>>>     // Work around NPTL stack guard error.
>>>     size_t guard_size = 0;
>>>     rslt = pthread_attr_getguardsize(&attr, &guard_size);
>>>     *bottom += guard_size;
>>>     *size   -= guard_size;
>>>
>>> So the net effect is hotspot treats the stack as only being 192k, not
>>> 256k. However, in terms of usable stack space, hotspot then also
>>> subtracts the red, yellow, and shadow zones. Each of these is one OS
>>> page. So that subtracts another 192k, leaving us with 0k. The assert is
>>> a by product of this.
>>>
>>> It turns out this pthread guard page problem is already fixed for all
>>> java threads except the main thread. We do the following in
>>> os::create_thread():
>>>
>>>   pthread_attr_setguardsize(&attr,
>>> os::Linux::default_guard_size(thr_type));
>>>
>>> For java threads, os::Linux::default_guard_size() returns 0, so the
>>> above code removes the guard page for java threads. The fix I'm
>>> proposing for the main thread does the same.
>>>
>>> Tested by running the test in question dozens of times on all supported
>>> platforms. Also ran most tests we do for nightlies except for longer
>>> running ones.
>>>
>>> thanks,
>>>
>>> Chris
>
>