[jdk19] RFR: 8288949: serviceability/jvmti/vthread/ContStackDepthTest/ContStackDepthTest.java failing [v2]

[Ron Pressler]

On Mon, 27 Jun 2022 08:17:01 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

>> src/hotspot/share/code/compiledMethod.cpp line 464:
>> 
>>> 462:   while(iter.next()) {
>>> 463:     if (iter.type() == relocInfo::static_call_type) {
>>> 464:       iter.reloc()->clear_inline_cache();
>> 
>> This relies on code patching, and for correctness the change must be seen by the thread requesting interpreter-only mode.  If this was being done at a safepoint then it would probably be OK.  However, this code seems to be done using a handshake, so I'm not sure if the required serializing instruction is guaranteed to happen (see JDK-8220351).  Maybe this race is OK, as it seems no worse than the scenario described in the description where another thread resets the call site back to the optimized state.
>
> The change is not guaranteed to be seen on a concurrent thread, until the next global handshake operation completes.

If that concurrent thread is in interp_only_mode, it also would have done the same patching. And if it isn't, then it's okay for it not to see this, but if it does see it, it will re-patch to compiled in c2i, as in the description.

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PR: https://git.openjdk.org/jdk19/pull/66