8342848: Shenandoah: Marking bitmap may not be completely cleared in generational mode

[pengxiaolong]

In the investigation of the crashe I saw in PR #516, I happened to reproduce the crash GenShen TIP as well.

The crash was reproduced multi times on both AWS r7g-4xlarge and r7i-4xlarge instances by running test below repeatedly:

CONF=linux-aarch64-server-fastdebug  make clean test TEST=gc/stress/gcold/TestGCOldWithShenandoah.java#generational JTREG="REPEAT_COUNT=1000" 

Crash:

#
# A fatal error has been detected by the Java Runtime Environment:
#
#  Internal Error (/home/xlpeng/repos/jdk-xlpeng/src/hotspot/share/gc/shenandoah/shenandoahConcurrentGC.cpp:642), pid=24134, tid=24158
#  assert(_generation->is_bitmap_clear()) failed: need clear marking bitmap
#
# JRE version: OpenJDK Runtime Environment (24.0) (fastdebug build 24-internal-adhoc.xlpeng.jdk-xlpeng)
# Java VM: OpenJDK 64-Bit Server VM (fastdebug 24-internal-adhoc.xlpeng.jdk-xlpeng, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, shenandoah gc, linux-aarch64)
# Problematic frame:
# V  [libjvm.so+0x15eadc4]  ShenandoahConcurrentGC::op_init_mark()+0x358
#
# No core dump will be written. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#
# An error report file with more information is saved as:
# /local/home/xlpeng/repos/jdk-xlpeng/build/linux-aarch64-server-fastdebug/test-support/jtreg_test_hotspot_jtreg_gc_stress_gcold_TestGCOldWithShenandoah_java_generational/scratch/0/hs_err_pid24134.log
#
# If you would like to submit a bug report, please visit:
#   https://bugreport.java.com/bugreport/crash.jsp
#

With logging/instrumentation, it seems to be caused by the one line code bool needs_reset = _generation->contains(region) || !region->is_affiliated(); , considering bitmap reset is a concurrent operation, if is possible mutator thread changes the affiliation from FREE to YOUNG when bitmap reset is running, both _generation->contains(region) and !region->is_affiliated() can be false when affiliation is FREE and mutator is updating it at the same time.

Logs from instrumentation:

[32.793s][info][gc          ] GC(19) Not reseting bitmap for YOUNG region (0x0000ffff8c1a6100)(affiliation before test: FREE)

...

[32.807s][info][gc,task     ] GC(20) Using 8 of 8 workers for init marking
[32.808s][info][gc          ] GC(20) Region (0x0000ffff8c1a6100) doesn't have clear bitmap, [1, 1, 1]

The fix is simple, just need to swap the two tests, !region->is_affiliated() should be evaluated prior to _generation->contains(region)

---

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Issue

• JDK-8342848: Shenandoah: Marking bitmap may not be completely cleared in generational mode (Bug - P4)

Reviewers

• William Kemper (@earthling-amzn - Committer) ⚠️ Review applies to ef777526

Reviewing

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Update a local copy of the PR:
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$ git pull https://git.openjdk.org/shenandoah.git pull/523/head

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Checkout this PR locally:
$ git pr checkout 523

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[openjdk]

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

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

8342848: Shenandoah: Marking bitmap may not be completely cleared in generational mode

Reviewed-by: wkemper

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At the time when this comment was updated there had been 1 new commit pushed to the master branch:

• 4970708: 8342580: GenShen: TestChurnNotifications fails executing in unintended test-id modes with ShenandoahGCMode=generational

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[mlbridge]

Webrevs

• 04: Full - Incremental (302bf4f0)
• 03: Full - Incremental (ef777526)
• 02: Full - Incremental (a798bcda)
• 01: Full - Incremental (548c6152)
• 00: Full (8cf581ec)

[pengxiaolong]

The test failure should not be caused by this change, spotted the same failure in other open PR:

java.lang.RuntimeException: expected testPhantom1 to be cleared
	at gc.shenandoah.TestReferenceRefersToShenandoah.fail(TestReferenceRefersToShenandoah.java:155)
	at gc.shenandoah.TestReferenceRefersToShenandoah.expectCleared(TestReferenceRefersToShenandoah.java:166)
	at gc.shenandoah.TestReferenceRefersToShenandoah.testConcurrentCollection(TestReferenceRefersToShenandoah.java:243)
	at gc.shenandoah.TestReferenceRefersToShenandoah.main(TestReferenceRefersToShenandoah.java:340)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
	at java.base/java.lang.reflect.Method.invoke(Method.java:573)
	at com.sun.javatest.regtest.agent.MainWrapper$MainTask.run(MainWrapper.java:138)
	at java.base/java.lang.Thread.run(Thread.java:1576)

JavaTest Message: Test threw exception: java.lang.RuntimeException: expected testPhantom1 to be cleared
JavaTest Message: shutting down test

` ``

[earthling-amzn]

Yes, we have a ticket for this test failure: https://bugs.openjdk.org/browse/JDK-8342734.

[earthling-amzn]

Nit, but shenandoah/shenandoahAffiliation.hpp should come between heuristics/shenandoahSpaceInfo.hpp and shenandoah/shenandoahGenerationType.hpp.

[pengxiaolong]

Fixed, thanks.

[earthling-amzn]

Okay with me to /integrate after fixing include order in shenandoahGeneration.hpp

[pengxiaolong]

/integrate

[openjdk]

@pengxiaolong
Your change (at version 302bf4f) is now ready to be sponsored by a Committer.

[earthling-amzn]

/sponsor

[openjdk]

Going to push as commit 55c6f67.
Since your change was applied there has been 1 commit pushed to the master branch:

• 4970708: 8342580: GenShen: TestChurnNotifications fails executing in unintended test-id modes with ShenandoahGCMode=generational

Your commit was automatically rebased without conflicts.

[openjdk]

@earthling-amzn @pengxiaolong Pushed as commit 55c6f67.

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