8322957: Generational ZGC: Relocation selection must join the STS

[stefank]

The concurrent ZGC threads don't automatically participate in the safepoint protocol, which means that they can run concurrently with safepoint VM Operations. Instead they use other means to hook into the safepoint protocol whenever they need to make changes that could be racing with the various VM Operations. The most common way is to join the "suspendible thread set". For details around this see SafepointSynchronize::begin and the call to Universe::heap()->safepoint_synchronize_begin().

It turns out that the relocation selection phase was updated to use a call oop_iterate, to modify oops of some of the objects. This was done without having the GC threads join the suspendible thread set. This means that various VM Operations could run concurrently with the oop_iterate. This caused the failure described in JDK-8322957: The JFR Leak Profiler modified the object header bits, while the GC's oop_iterate function used the same bits to determine if the oop iteration over an object should be skipped. This lead to objects not being modified as they were supposed to, which lead to broken oops and asserts.

The fix is quite small and could be limited to the lines added to src/hotspot/share/gc/z/zRelocationSet.cpp. However, to lower the risk of reintroducing a bug like this again, we've added extra verification code. Some of the infrastructure to get the correct verification is placed outside of the GC code, and that's why this PR is sent to the hotspot-dev list.

This has been tested with the reproducer of the original bug + tier1-7 on linux-x64-debug.

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Issue

• JDK-8322957: Generational ZGC: Relocation selection must join the STS (Bug - P2)

Reviewers

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

Contributors

• Axel Boldt-Christmas <aboldtch@openjdk.org>

Reviewing

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[stefank]

/label add hotspot

[stefank]

/contributor add @xmas92

[bridgekeeper]

👋 Welcome back stefank! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

@stefank
The hotspot label was successfully added.

[openjdk]

@stefank
Contributor Axel Boldt-Christmas <aboldtch@openjdk.org> successfully added.

[mlbridge]

Webrevs

• 01: Full - Incremental (6e5664c2)
• 00: Full (54218a84)

[fisk]

Looks good.

[openjdk]

@stefank This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8322957: Generational ZGC: Relocation selection must join the STS

Co-authored-by: Axel Boldt-Christmas <aboldtch@openjdk.org>
Reviewed-by: eosterlund, aboldtch

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 77 new commits pushed to the master branch:

• 9fd855e: 8322971: KEM.getInstance() should check if a 3rd-party security provider is signed
• b8ae4a8: 8320890: [AIX] Find a better way to mimic dl handle equality
• e5aed6b: 8323276: StressDirListings.java fails on AIX
• b922f8d: 8319793: C2 compilation fails with "Bad graph detected in build_loop_late" after JDK-8279888
• 35e9662: 8314515: java/util/concurrent/SynchronousQueue/Fairness.java failed with "Error: fair=false i=8 j=0"
• cb1d25f: 8323330: [BACKOUT] JDK-8276809: java/awt/font/JNICheck/FreeTypeScalerJNICheck.java shows JNI warning on Windows
• 2b7fc05: 8264102: JTable Keyboards Navigation differs with Test Instructions.
• af942a6: 8323188: JFR: Needless RESOURCE_ARRAY when sending EventOSInformation
• 26de9e2: 8321616: Retire binary test vectors in test/jdk/java/util/zip/ZipFile
• b530c02: 8317804: com/sun/jdi/JdwpAllowTest.java fails on Alpine 3.17 / 3.18
• ... and 67 more: https://git.openjdk.org/jdk/compare/71aac7a5fbb9a32181ada1a04b6a9622fe939c59...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[xmas92]

lgtm.

[stefank]

Tier1-7 passes.

[stefank]

/integrate

[openjdk]

Going to push as commit ba23025.
Since your change was applied there have been 91 commits pushed to the master branch:

• 7c3a39f: 8323297: Fix incorrect placement of precompiled.hpp include lines
• e72723d: 8323296: java/lang/Thread/virtual/stress/GetStackTraceALotWhenPinned.java#id1 timed out
• 66520be: 8280056: gtest/LargePageGtests.java#use-large-pages failed "os.release_one_mapping_multi_commits_vm"
• 82a63a0: 8258979: The image didn't show correctly with GTK LAF
• 8d9814a: 8322757: Enable -Wparentheses warnings
• 0ff2dea: 8320673: PageFormat/CustomPaper.java has no Pass/Fail buttons; multiple instructions
• 8e12053: 8322799: Test JPKG003-013: ServiceTest fails because the user cannot uninstall the "servicetest" package on OEL 9.2 x64 and OEL 9.2 64-bit Arm (aarch64)
• e4389d8: 8323571: Regression in source resolution process
• 49e6121: 8310813: Simplify and modernize equals, hashCode, and compareTo for BigInteger
• 4ea7b36: 8322235: Split up and improve LocaleProvidersRun
• ... and 81 more: https://git.openjdk.org/jdk/compare/71aac7a5fbb9a32181ada1a04b6a9622fe939c59...master

Your commit was automatically rebased without conflicts.

[openjdk]

@stefank Pushed as commit ba23025.

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