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

[David Holmes]

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
>