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

Chris Plummer chris.plummer at oracle.com
Thu Mar 16 05:49:57 UTC 2017

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.
Ok. I'll move the pthread_attr_setguardsize() call to just below the 
"if" block.

Thanks for the review.

> 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

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