(9) RFR: 8064815 Zero+PPC64: Stack overflow when running Maven

[Severin Gehwolf]

Hi Volker,

On Fri, 2014-11-14 at 14:46 +0100, Volker Simonis wrote:
> Hi Severin,
> 
> I can sponsor this change if we get one more review.

Thanks!

> The only comment I have is that in ZeroStack::suggest_size() there
> doesn't seem to be a handling for the potentially negative values
> returned by ZeroStack::abi_stack_available().

OK. I could do something like this. 

diff --git a/src/cpu/zero/vm/stack_zero.cpp
b/src/cpu/zero/vm/stack_zero.cpp
--- a/src/cpu/zero/vm/stack_zero.cpp
+++ b/src/cpu/zero/vm/stack_zero.cpp
@@ -30,7 +30,9 @@
 
 int ZeroStack::suggest_size(Thread *thread) const {
   assert(needs_setup(), "already set up");
-  return align_size_down(abi_stack_available(thread) / 2, wordSize);
+  ssize_t abi_available = abi_stack_available(thread);
+  assert(abi_available >= 0, "available abi stack must be >= 0");
+  return align_size_down(abi_available / 2, wordSize);
 }

Did you have something else in mind? I'm not sure if it's necessary
since suggest_size is only being called when the zero stack is set up
(src/cpu/zero/vm/stubGenerator_zero.cpp). Thoughts?

Thanks,
Severin

> On Fri, Nov 14, 2014 at 2:18 PM, Severin Gehwolf <sgehwolf at redhat.com> wrote:
> > Hi,
> >
> > Could I please get a review and sponsor for the following fix:
> >
> > bug: https://bugs.openjdk.java.net/browse/JDK-8064815
> > webrev:
> > https://jerboaa.fedorapeople.org/bugs/openjdk/JDK-8064815/webrev.0/
> >
> > When running Maven ("mvn") on a Zero variant build on PPC/PPC64 hardware
> > it throws a StackOverflowError. This is because the stack bound
> > calculation does not account for red and yellow pages.
> >
> > The bug has a slightly different patch attached. The changes to
> > hotspot/src/os/linux/vm/os_linux.cpp aren't needed for this bug.
> >
> > Testing done: A Zero variant build of OpenJDK 9 on PPC/PPC64 throws
> > StackOverflowError without this fix and works fine with this fix
> > applied.
> >
> > Note that this problem seems to surface on architectures where pages are
> > large. PPC is one such instance. Page size there is 64KB and Zero
> > initially sets its minimal stack allowance to 64KB (one page),
> > src/os_cpu/linux_zero/vm/os_linux_zero.cpp. In os::init_2 this gets
> > potentially increased if min_stack_allowed is small. The case on PPC
> > Zero.
> >
> > However, then later at runtime the calculation of available stack is
> > wrong since it does not account for red and yellow pages. Thus it thinks
> > there is too little stack available where in fact more stack is
> > available.
> >
> > Thanks,
> > Severin
> >