[9] RFR (S) 6762191: Setting stack size to 16K causes segmentation fault

[David Holmes]

On 19/11/2014 6:49 PM, Chris Plummer wrote:
> I've update the webrev to add STACK_SIZE_MINIMUM in place of the 32k
> references, and also moved the test from hotspot/test/runtime to
> jdk/test/tools/launcher as David requested. That required some
> adjustments to the test script, since test_env.sh does not exist in
> jdk/test, so I had to pull in the bits I needed into the script.

Is there a reason this needs a shell script instead of using the 
testlibrary tools to launch the VM and check the output?

Sorry that should have been mentioned much earlier.

David


> http://cr.openjdk.java.net/~cjplummer/6762191/webrev.01/
>
> I still need to rerun through JPRT. I'll do so once there are no more
> suggested changes.
>
> thanks,
>
> Chris
>
> On 11/18/14 2:08 PM, Chris Plummer wrote:
>> Adding core-libs-dev at openjdk.java.net, since one of the changes is in
>> java.c.
>>
>> Chris
>>
>> On 11/12/14 6:43 PM, David Holmes wrote:
>>> Hi Chris,
>>>
>>> Sorry for the delay.
>>>
>>> On 13/11/2014 5:44 AM, Chris Plummer wrote:
>>>> Hi,
>>>>
>>>> I'm still looking for reviewers.
>>>
>>> As the change is to the launcher it needs to be reviewed by the
>>> launcher owner - which I think is serviceability (though also cc'd
>>> Kumar :) ).
>>>
>>> Launcher change, and your rationale, seems okay to me. I'd probably
>>> put the test in to jdk/test/tools/launcher/ though.
>>>
>>> Thanks,
>>> David
>>>
>>>> thanks,
>>>>
>>>> Chris
>>>>
>>>> On 11/7/14 7:53 PM, Chris Plummer wrote:
>>>>> This is an initial review for 6762191. I'm guessing there will be
>>>>> recommendations to fix in a different way, but thought this would be a
>>>>> good time to start the discussion.
>>>>>
>>>>> https://bugs.openjdk.java.net/browse/JDK-6762191
>>>>> http://cr.openjdk.java.net/~cjplummer/6762191/webrev.00.jdk/
>>>>> http://cr.openjdk.java.net/~cjplummer/6762191/webrev.00.hotspot/
>>>>>
>>>>> The bug is that if the -Xss size is set to something very small (like
>>>>> 16k), on linux there will be a crash due to overwriting the end of the
>>>>> stack. This happens before hotspot can compute its stack needs and
>>>>> verify that the stack is big enough.
>>>>>
>>>>> It didn't seem viable to move the hotspot stack size check earlier. It
>>>>> depends on too much other work done before that point, and the changes
>>>>> would have been disruptive. The stack size check is currently done in
>>>>> os::init_2().
>>>>>
>>>>> What is needed is a check before the thread is created. That way we
>>>>> can create a thread with a big enough stack to handle all needs up to
>>>>> the point of the check in os::init_2(). This initial check does not
>>>>> need to be the final check. It just needs to confirm that we have
>>>>> enough stack to get us to the check in os::init_2().
>>>>>
>>>>> I decided to check in java.c if the -Xss size is too small, and set it
>>>>> to a larger size if it is. I hard coded this size to 32k (I'll explain
>>>>> why 32k later). I suspect this is the part that will result in some
>>>>> debate. If you have better suggestions let me know. If it does stay
>>>>> here, then probably the 32k needs to be a #define, and maybe even an
>>>>> OS porting interface, but I'm not sure where to put it.
>>>>>
>>>>> The reason I chose 32k is because this is big enough for all platforms
>>>>> to get to the stack size check in os::init_2(). It is also smaller
>>>>> than the actual minimum stack size allowed on any platform. 32-bit
>>>>> windows has the smallest requirement at 64k. I add some printfs to
>>>>> print the minimum stack requirement, and then ran a simple JTReg test
>>>>> with every JPRT supported platform to get the results.
>>>>>
>>>>> The TooSmallStackSize.sh will run "java -version" with -Xss16k,
>>>>> -Xss32k, and -XXss<minsize>, where <minsize> is the size from the
>>>>> error message produced by the JVM, such as in the following:
>>>>>
>>>>> $ java -Xss32k -version
>>>>> The stack size specified is too small, Specify at least 100k
>>>>> Error: Could not create the Java Virtual Machine.
>>>>> Error: A fatal exception has occurred. Program will exit.
>>>>>
>>>>> I ran this test through JPRT on all platforms, and they all pass.
>>>>>
>>>>> One thing to point out is that Windows behaves a bit different than
>>>>> the other platforms. It always rounds the stack size up to a multiple
>>>>> of 64k , so even if you specify -Xss16k, you get a 64k stack. On
>>>>> 32-bit Windows with C1, 64k is also the minimum requirement, so there
>>>>> is no error produced in this case. However, on 32-bit Windows with C2,
>>>>> 68k is the minimum, so an error is produced since the stack will only
>>>>> be 64k. There is no bug here. It's just a bit confusing.
>>>>>
>>>>> thanks,
>>>>>
>>>>> Chris
>>>>
>>
>