On Wed, 4 Sep 2024 15:23:51 GMT, Maurizio Cimadamore <mcimadam...@openjdk.org> wrote:
> Scoped methods are critical methods in the FFM API where memory is accessed > in a potentially unsafe way. When closing shared arenas, we look at threads > in the middle of a scoped operation involving that arena, and if we find one, > we make it fail (by installing an async handshake on that thread). > > To find whether a thread is in a scoped method or not, we need a stack walk. > For performance reasons, it is preferrable to have the stack walk to be > bounded in size. > > A test started picking up a JVM assertion where the stack of a scoped method > (namely `ScopedMemoryAccess::isLoaded`) is too big. This is caused by the > scoped method stack walk finding the thread using the scoped method in the > middle of some JNI lookup (which is required as `isLoaded` eventually ends up > in a native method). This condition seems to have been made easier by the > fact that these [changes](https://git.openjdk.org/jdk/pull/19213). > > This PR reverts the stack trace associated with JNI lookup to what it was > before, by eliminating the extra frame with a bit of refactoring/cleanup. But > this is not enough: the stress test introduced in this PR still fails, even > when the stack associated with `ClassLoader::findNative` is restored. > > To address this problem in full, I have resorted to `registerNatives` - that > is, the native `isLoaded0`, `load0`, `unload0` and `force0` are > pre-registered, when the static initializer of `MappedMemoryUtils` is ran. > This means that we no longer need to run a JNI lookup in the middle of a > scoped method call. This brings the stack back under control, and passes the > stress test. > > Of course there's more to do in this area - we should have a more direct test > to check the stack associated with scoped methods (for instance, vector > load/store operations are also potential suspects), in order to catch > "suspicious refactoring" earlier in the process. For this reason I also filed > a follow up i[ssue](https://bugs.openjdk.org/browse/JDK-8339551). This pull request has now been integrated. Changeset: 9e1af8cc Author: Maurizio Cimadamore <mcimadam...@openjdk.org> URL: https://git.openjdk.org/jdk/commit/9e1af8cc7cc9f63453097bd35eb3cf29f945d765 Stats: 253 lines in 9 files changed: 212 ins; 12 del; 29 mod 8339285: Test fails with assert(depth < max_critical_stack_depth) failed: can't have more than 10 critical frames Reviewed-by: alanb ------------- PR: https://git.openjdk.org/jdk/pull/20854
