Hi Richard, Thank you for filing the CR and taking care about it! The fix itself looks good to me. I still need another look at new test. Could you, please, convert the agent of new test to C++? It will make it a little bit simpler.
Thanks, Serguei On 7/20/20 01:15, Reingruber, Richard wrote:
Hi, please help review this fix for VM_GetOrSetLocal. It moves the unsafe stackwalk from the vm operation prologue before the safepoint into the doit() method executed at the safepoint. Webrev: http://cr.openjdk.java.net/~rrich/webrevs/8249293/webrev.0/index.html Bug: https://bugs.openjdk.java.net/browse/JDK-8249293 According to the JVMTI spec on local variable access it is not required to suspend the target thread T [1]. The operation will simply fail with JVMTI_ERROR_NO_MORE_FRAMES if T is executing bytecodes. It will succeed though if T is blocked because of synchronization or executing some native code. The issue is that in the latter case the stack walk in VM_GetOrSetLocal::doit_prologue() to prepare the access to the local variable is unsafe, because it is done before the safepoint and it races with T returning to execute bytecodes making its stack not walkable. The included test shows that this can crash the VM if T wins the race. Manual testing: - new test test/hotspot/jtreg/serviceability/jvmti/GetLocalVariable/GetLocalWithoutSuspendTest.java - test/hotspot/jtreg/vmTestbase/nsk/jvmti - test/hotspot/jtreg/serviceability/jvmti Nightly regression tests @SAP: JCK and JTREG, also in Xcomp mode, SPECjvm2008, SPECjbb2015, Renaissance Suite, SAP specific tests with fastdebug and release builds on all platforms Thanks, Richard. [1] https://docs.oracle.com/en/java/javase/14/docs/specs/jvmti.html#local
