RFR: 8277444: Data race between JvmtiClassFileReconstituter::copy_bytecodes and class linking [v4]

[Coleen Phillimore]

On Fri, 29 Aug 2025 22:48:06 GMT, Evgeny Astigeevich <eastigeevich at openjdk.org> wrote:

>> There is a race between `JvmtiClassFileReconstituter::copy_bytecodes` and `InstanceKlass::link_class_impl`.  `InstanceKlass::link_class_impl` can be rewriting bytecodes. `JvmtiClassFileReconstituter::copy_bytecodes` will not restore them to the original ones because the flag `rewritten` is `false`. This will result in invalid bytecode.
>> 
>> This PR adds linking a class before the `copy_bytecodes` method is called.
>> The PR also adds a regression test.
>> 
>> Tested fastdebug and release builds: Linux x86_64 and arm64
>> - The reproducer from JDK-8277444 passed.
>> - The regression test passed.
>> - Tier1 - tier3 passed.
>
> Evgeny Astigeevich has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:
> 
>  - Merge branch 'master' into JDK-8277444
>  - Link classes before copy_bytecodes; Add regression test
>  - Symplify comments; Get JavaThread::current in variable
>  - Add missing include runtime/synchronizer.hpp
>  - 8277444: Race condition on Instrumentation.retransformClasses() and class linking

I had a couple of minor comments but otherwise looks good.  Is the test now reliable?  Thank you for adding a test.

src/hotspot/share/prims/jvmtiClassFileReconstituter.cpp line 35:

> 33: #include "runtime/handles.inline.hpp"
> 34: #include "runtime/signature.hpp"
> 35: #include "runtime/synchronizer.hpp"

You don't need this include anymore.

src/hotspot/share/prims/jvmtiEnv.cpp line 3446:

> 3444:     current_thread->clear_pending_exception();
> 3445:     return JVMTI_ERROR_INVALID_CLASS;
> 3446:   }

Can you use the pattern:


    JavaThread* THREAD = current_thread;
    ... link_class(THREAD);
    if (HAS_PENDING_EXCEPTION)
      etc.

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PR Review: https://git.openjdk.org/jdk/pull/26863#pullrequestreview-3176231981
PR Review Comment: https://git.openjdk.org/jdk/pull/26863#discussion_r2315873660
PR Review Comment: https://git.openjdk.org/jdk/pull/26863#discussion_r2315880585