8348907: Stress times out when is executed with ZGC

[mgronlun]

Greetings,

Here is a suggested solution for solving the intricate deadlock issues involving virtual threads, ZGC load barriers, and JFR.

A JFR event can be allocated and committed in specific sensitive contexts, such as inside mutex-protected load barriers. If the thread is a virtual thread, JFR determines its thread name by loading the oop from the thread (jt->vthread()) as part of the event commit.

This operation again triggers the load barrier, which contains a non-reentrant lock, effectively deadlocking the thread with itself.

So, for specific sensitive event sites, JFR mustn't recurse or reenter into the same event site as part of the event commit.

After a few iterations and prototypes, which failed because they eventually ended up touching some oop, I came up with the following.

From a user perspective, an event (site) can now be marked as "non-reentrant" by wrapping it in a helper class.

This instruction now guarantees JFR will not reenter this site again as part of the event.commit().

The tradeoff is that we cannot write the virtual thread name for these sensitive event sites; we will instead report "" as the virtual thread name, which is the default virtual thread name in Java. All other information about the thread, such as the thread ID, virtual thread, etc., will still be reported.

I believe it is a reasonable tradeoff and a general solution for sensitive JFR event sites, which are rare in practice, with minimal impact on event programming.

Testing: jdk_jfr, stress testing

Let me know what you think.

Thanks
Markus

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Issue

• JDK-8348907: Stress times out when is executed with ZGC (Bug - P3)

Reviewers

• Erik Gahlin (@egahlin - Reviewer)
• Axel Boldt-Christmas (@xmas92 - Reviewer)
• Erik Österlund (@fisk - Reviewer)

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At the time when this comment was updated there had been 29 new commits pushed to the master branch:

• 79bffe2: 8349361: C2: RShiftL should support all applicable transformations that RShiftI does
• eef6aef: 8352623: MultiExchange should cancel exchange impl if responseFilters throws
• e2a461b: 8351332: Line breaks in search tag descriptions corrupt JSON search index
• c14bbea: 8352740: Introduce new factory method HtmlTree.IMG
• 84d3dc7: 8352965: [BACKOUT] 8302459: Missing late inline cleanup causes compiler/vectorapi/VectorLogicalOpIdentityTest.java IR failure
• b4dc364: 8346931: Replace divisions by zero in sharedRuntimeTrans.cpp
• bc5cde1: 8352692: Add support for extra jlink options
• 059f190: 8352490: Fatal error message for unhandled bytecode needs more detail
• ee710fe: 8345169: Implement JEP 503: Remove the 32-bit x86 Port
• eb6e828: 8351002: com/sun/management/OperatingSystemMXBean cpuLoad tests fail intermittently
• ... and 19 more: https://git.openjdk.org/jdk/compare/bab93729c26907dc51d15dbb5651f860f0cb58ab...master

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[xmas92]

Looks like a pragmatic solution.

I am not reviewing the the implications of not setting the epoch, as my understanding here is a bit lacking.

The name JfrNonReentrant seems a little general for how tightly coupled the property is to running on a virtual thread and loading an oop. At the same time this is currently the only interaction which exhibits problems with reentry, and I am not sure if there is a better name.

[fisk]

This seems like a pragmatic workaround for the problem. We might want to revisit this at some point to make it easier to use JFR in the GC code, but I think this is an appropriate fix for the bug right now. Thanks for fixing this Markus.

[mgronlun]

/integrate

[openjdk]

Going to push as commit c2a4fed.
Since your change was applied there have been 32 commits pushed to the master branch:

• 5392674: 8352766: Problemlist hotspot tier1 tests requiring tools that are not included in static JDK
• 1d205f5: 8352716: (tz) Update Timezone Data to 2025b
• a2a64da: 8352588: GenShen: Enabling JFR asserts when getting GCId
• 79bffe2: 8349361: C2: RShiftL should support all applicable transformations that RShiftI does
• eef6aef: 8352623: MultiExchange should cancel exchange impl if responseFilters throws
• e2a461b: 8351332: Line breaks in search tag descriptions corrupt JSON search index
• c14bbea: 8352740: Introduce new factory method HtmlTree.IMG
• 84d3dc7: 8352965: [BACKOUT] 8302459: Missing late inline cleanup causes compiler/vectorapi/VectorLogicalOpIdentityTest.java IR failure
• b4dc364: 8346931: Replace divisions by zero in sharedRuntimeTrans.cpp
• bc5cde1: 8352692: Add support for extra jlink options
• ... and 22 more: https://git.openjdk.org/jdk/compare/bab93729c26907dc51d15dbb5651f860f0cb58ab...master

Your commit was automatically rebased without conflicts.

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@mgronlun Pushed as commit c2a4fed.

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