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

[Chris Plummer]

Sorry about the long delay in getting back to this. I ran into two 
separate JPRT issues that were preventing me from testing these changes, 
plus I was on vacation last week. Here's an updated webrev. I'm not sure 
where we left things, so I'll just say what's changed since the original 
version:

1. Rewrote the test to be in Java instead of a shell script.
2. Moved the test from hotspot/test/runtime/memory to 
jdk/test/tools/launcher
3. Added STACK_SIZE_MINIMUM to java.c, allowing a makefile to override 
the default 32k minimum value.

https://bugs.openjdk.java.net/browse/JDK-6762191
http://cr.openjdk.java.net/~cjplummer/6762191/webrev.02/

thanks,

Chris

On 11/19/14 7:52 AM, Chris Plummer wrote:
On 11/19/14 2:12 AM, David Holmes wrote:
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?
Not that I'm aware of. I guess I just really didn't look at what it 
would take to make it all in java. I'll have a look at java examples 
and convert it.

Chris

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-...@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