On Thu, 19 Dec 2024 21:04:51 GMT, Robert Toyonaga <d...@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 > > Robert Toyonaga has updated the pull request incrementally with one > additional commit since the last revision: > > Revert to using NmtVirtualMemoryLocker. Use defaultStream. Add comment for > SharedDecoder_lock I had a few minor comments and hopefully easy changes to make. src/hotspot/share/nmt/virtualMemoryTracker.cpp line 421: > 419: assert(_reserved_regions != nullptr, "Sanity check"); > 420: assert(!MemTracker::is_done_bootstrap() || > NmtVirtualMemory_lock->owned_by_self() , "Should have acquired > NmtVirtualMemory_lock"); > 421: You could add this to MemTracker class like: ``` inline static void assert_locked(); Then put the body void MemTracker::assert_locked() { assert(!is_bootstrapping_done() || NmtVirtualMemory_lock->owned_by_self(), "should have acquired NmtVirtualMemory_lock"); } Then all these calls could be MemTracker::assert_locked(). src/hotspot/share/nmt/virtualMemoryTracker.cpp line 631: > 629: > 630: bool do_allocation_site(const ReservedMemoryRegion* rgn) { > 631: assert_lock_strong(NmtVirtualMemory_lock); So this is past bootstrapping? src/hotspot/share/runtime/mutexLocker.cpp line 292: > 290: MUTEX_DEFN(NMTCompilationCostHistory_lock , PaddedMutex , > nosafepoint); > 291: MUTEX_DEFN(NmtVirtualMemory_lock , PaddedMutex , > service-4); // Must be lower than G1Mapper_lock used from > G1RegionsSmallerThanCommitSizeMapper::commit_regions > 292: #if INCLUDE_CDS Yes, this looks good. I see why you couldn't move this one to MUTEX_DEFL. ------------- Changes requested by coleenp (Reviewer). PR Review: https://git.openjdk.org/jdk/pull/22745#pullrequestreview-2517782112 PR Review Comment: https://git.openjdk.org/jdk/pull/22745#discussion_r1894080029 PR Review Comment: https://git.openjdk.org/jdk/pull/22745#discussion_r1894080796 PR Review Comment: https://git.openjdk.org/jdk/pull/22745#discussion_r1894084698
