[jdk25u] RFR: 8277444: Data race between JvmtiClassFileReconstituter::copy_bytecodes and class linking

[Chad Rakoczy]

On Fri, 12 Sep 2025 21:26:04 GMT, Chad Rakoczy <duke at openjdk.org> wrote:

> A clean backport of https://bugs.openjdk.org/browse/JDK-8277444
> 
> This fixes a race condition that occurs when a class is simultaneously retransformed via the Instrumentation API and linked. This can lead to invalid bytecode which will cause a VerifyError. Even worse, if class verifying is turned off, which it is by default for java.* classes, this will cause the JVM to crash/segfault. 
> 
> The included test `test/jdk/java/lang/instrument/RetransformBigClassTest.java` fails before the patch and passes after

Test passed on GHA rerun

-------------

PR Comment: https://git.openjdk.org/jdk25u/pull/197#issuecomment-3300316740