Hi Dan,
Great find in getting to the bottom of this one!
On 20/10/2015 1:02 PM, Daniel D. Daugherty wrote:
Greetings,
I have a fix for a long standing race between the lock-free ObjectMonitor
verification code and the normal (locked) ObjectMonitor block allocation
code path. For this fix, I would like at least a Runtime team reviewer
and a Serviceability team reviewer. Thanks!
JDK-8047212 runtime/ParallelClassLoading/bootstrap/random/inner-complex
assert(ObjectSynchronizer::verify_objmon_isinpool(inf))
failed:
monitor is invalid
https://bugs.openjdk.java.net/browse/JDK-8047212
Webrev URL: http://cr.openjdk.java.net/~dcubed/8047212-webrev/0-jdk9-hs-rt/
src/share/vm/runtime/synchronizer.cpp
I would have just used OrderAccess::storeStore() as per my comment in
the CR. But as Carsten says a "release" should be paired with an
"acquire". Which suggests that in the other code that reads these
variables we also need either the load_acquire() or a loadLoad() (if
using storeStore()).**
** This symmetry is largely missing in our lock-free code, and I think
we've been relying on "volatile" to act as a compiler barrier. :(
src/share/vm/runtime/vmStructs.cpp
Can you not just define volatile_static_field? Why does the ptr aspect
need to come into it? Also "static pointer volatile field" sounds really
odd, it is a static, volatile field that happens to be a pointer-type.
Thanks,
David
Testing: Aurora Adhoc RT-SVC nightly batch
4 inner-complex fastdebug parallel runs for 4+ days and
600K iterations without seeing this failure; the experiment
is still running; final results to be reported at the end
of the review cycle
JPRT -testset hotspot
This fix:
- makes ObjectMonitor::gBlockList volatile
- uses "OrderAccess::release_store_ptr(&gBlockList, temp)" to
make sure the new block updates _happen before_ gBlockList is
changed to refer to the new block
- add SA support for a "static pointer volatile" field like:
static ObjectMonitor * volatile gBlockList;
See the following link for a nice description of what "volatile"
means in the different positions on a variable/parameter decl line:
http://www.embedded.com/electronics-blogs/beginner-s-corner/4023801/Introduction-to-the-Volatile-Keyword
Thanks, in advance, for any comments, questions or suggestions.
Dan
