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

[Dmitry Samersoff]

Chris,

Looks good to me.

-Dmitry

On 2017-03-17 10:31, Chris Plummer wrote:
> 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
>>
>>
> 


-- 
Dmitry Samersoff
Oracle Java development team, Saint Petersburg, Russia
* I would love to change the world, but they won't give me the sources.