On Mon, 16 Dec 2024 22:15:45 GMT, Kim Barrett <kbarr...@openjdk.org> wrote:
>> This is a redo of [JDK-8304824](https://bugs.openjdk.org/browse/JDK-8304824) >> which was backed out by >> [JDK-8343726](https://bugs.openjdk.org/browse/JDK-8343726) due to problems >> documented in [JDK-8343244](https://bugs.openjdk.org/browse/JDK-8343244). >> >> The problem was that `NmtVirtualMemoryLocker` was not locking when the >> current thread is not attached by checking `Thread::current_or_null_safe() >> != nullptr`. This is necessary during VM init, but should not be allowed >> afterward. NMT may be used in `attach_current_thread` before the current >> thread is set. The lock was not being acquired in that case, which >> intermittently caused NMT accounting to become corrupted, triggering various >> assertions when future NMT operations are done. To fix this, I've adopted >> [Thomas' >> suggestion](https://github.com/openjdk/jdk/pull/21928#issuecomment-2460238057) >> to reverse the order of >> >> >> thread->register_thread_stack_with_NMT(); >> thread->initialize_thread_current(); >> >> >> in `attach_current_thread`. This allows `NmtVirtualMemoryLocker` to be >> locked after current thread is set. >> >> To allow for `NmtVirtualMemoryLocker` to be used during VM init, I've >> replaced the `ConditionalMutexLocker` check `Thread::current_or_null_safe() >> != nullptr` with a new flag: `_done_bootstrap`. This flag prevents the lock >> from being used during VM init, at which point we are single threaded >> anyway. This avoids errors due to Hotspot mutexes and current thread not yet >> being ready. >> >> I also added new asserts in `virtualMemoryTracker.cpp` to catch future bugs >> like this where the lock is not held when it should be. I updated the >> appropriate VMT tests to also lock (there were a few cases where locking was >> being bypassed) so they can pass the new asserts. >> >> I also removed the unused `_query_lock` variable in `MemTracker`. >> >> Testing: >> >> - On Linux amd64, I was able to consistently reproduce the errors described >> in [JDK-8343244](https://bugs.openjdk.org/browse/JDK-8343244) by increasing >> the number of test threads in >> `java/lang/Thread/jni/AttachCurrentThread/AttachTest.java`. The test >> consistently passes with the new changes in this PR. >> - hotspot_nmt , gtest:VirtualSpace, tier1 > > src/hotspot/share/nmt/memTracker.hpp line 281: > >> 279: // Same as MutexLocker but can be used during VM init while single >> threaded and before mutexes are ready or current thread has been assigned. >> 280: // Performs no action during VM init. >> 281: class NmtVirtualMemoryLocker: public ConditionalMutexLocker { > > Should not derive from ConditionalMutexLocker - it's not designed to be a > base class. > Either use has-a relationship, or just derive directly from MutexLockerImpl, > since we don't need > the assert in ConditionalMutexLocker anyway. And I'm surprised there isn't a > constructor taking > the current thread, like all the other locker variants. You should be able to use a ConditionalMutexLocker directly to handle this situation - it is one of the usecases that caused CML to be introduced. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/22745#discussion_r1887738017