8277631: ZGC: CriticalMetaspaceAllocation asserts #6520

fisk · 2021-11-23T14:14:31Z

The MetaspaceCritical_lock is a non-safepoint checking lock. That implies that the allow VM block flag is true. That implies that taking that lock takes a NoSafepointVerifier. That causes an assert to fire when MetaspaceCriticalAllocation::wait_for_purge transitions to blocked with ThreadBlockInVM while holding the lock. The fix is to move the locker inside of the ThreadBlockInVM.

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Issue

JDK-8277631: ZGC: CriticalMetaspaceAllocation asserts

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Per Liden (@pliden - Reviewer) ⚠️ Review applies to ec93bed
Stefan Karlsson (@stefank - Reviewer) ⚠️ Review applies to ec93bed
David Holmes (@dholmes-ora - Reviewer) ⚠️ Review applies to ec93bed

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bridgekeeper · 2021-11-23T14:16:01Z

👋 Welcome back eosterlund! 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 · 2021-11-23T14:18:14Z

@fisk The following label will be automatically applied to this pull request:

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mlbridge · 2021-11-23T14:22:46Z

Webrevs

01: Full - Incremental (ea651174)
00: Full (ec93bede)

openjdk · 2021-11-23T14:35:14Z

@fisk 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:

8277631: ZGC: CriticalMetaspaceAllocation asserts

Reviewed-by: pliden, stefank, dholmes

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 34 new commits pushed to the master branch:

7b2d823: 8277503: compiler/onSpinWait/TestOnSpinWaitAArch64DefaultFlags.java failed with "OnSpinWaitInst with the expected value 'isb' not found."
7cb56a2: 8265796: vmTestbase/nsk/jdi/ObjectReference/referringObjects/referringObjects002/referringObjects002.java fails when running with JEP 416
24e586a: 8276764: Enable deterministic file content ordering for Jar and Jmod
ea85e01: 8271623: Omit enclosing instance fields from inner classes that don't use it
0320672: 8277451: java.lang.reflect.Field::set on static field with invalid argument type should throw IAE
e8acac2: 8277350: runtime/jni/checked/TestPrimitiveArrayCriticalWithBadParam.java times out
8a44e09: 8268725: jshell does not support the --enable-native-access option
7b67a49: 8261847: performance of java.lang.Record::toString should be improved
38802ad: 8254108: ciReplay: Support incremental inlining
64bdc84: 8277649: [BACKOUT] JDK-8277507 Add jlink.debug system property while launching jpackage tests to help diagonize recent intermittent failures
... and 24 more: https://git.openjdk.java.net/jdk/compare/3f847fe89a088d6921107ca887a7a1bace871bd6...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.

fisk · 2021-11-23T14:43:03Z

Thanks for the reviews, @pliden and @stefank!

dholmes-ora

Just a comment but it always concerns me that if we have to manually add a TBIVM when using a non-safepoint-checking lock then the lock is mis-classified as a non-safepoint-checking one! :(

That aside changes look fine. A few grammatical nits in the test.

Thanks,
David

dholmes-ora · 2021-11-24T05:15:34Z

src/hotspot/share/memory/metaspaceCriticalAllocation.cpp

+  for (;;) {
    ThreadBlockInVM tbivm(JavaThread::current());


Can't you move the TBIVM outside of the loop now that it is always created?

Just a comment but it always concerns me that if we have to manually add a TBIVM when using a non-safepoint-checking lock then the lock is mis-classified as a non-safepoint-checking one! :(

That aside changes look fine. A few grammatical nits in the test.

Thanks, David

Thanks for the review David. I fixed your nits.

I agree that this lock should preferably have been a safepoint checking lock. In fact, it was a safepoint checking lock when I wrote the code. But that was before we changed the locking rules so that whether we do safepoint checking or not is a function of the rank. After that, this lock has become constrained to the current low rank by the current set of other locks, and by being that low ish rank, it is not allowed to safepoint check, unless I move a bunch of other lock ranks around, and figure out if it's okay for those locks to start safepoint checking as well, which isn't entirely obvious.

So this lock might be a case where those new rules end up being a bit awkward, and have lead this code to do manual transitions to blocked instead, as an escape hatch from the asserts.

Ah! I forgot about the rank changes that forced this dichotomy.

dholmes-ora · 2021-11-24T05:15:34Z

test/hotspot/jtreg/vmTestbase/gc/gctests/LoadUnloadGC/LoadUnloadGC.java

+ * @summary converted from VM Testbase gc/gctests/LoadUnloadGC.
+ * VM Testbase keywords: [gc, stress, stressopt, nonconcurrent, monitoring]
+ * VM Testbase readme:
+ * In this test a 1000 classes are loaded and unloaded in a loop.


nit: /a 1000/1000/

dholmes-ora · 2021-11-24T05:15:34Z

test/hotspot/jtreg/vmTestbase/gc/gctests/LoadUnloadGC/LoadUnloadGC.java

+ * VM Testbase readme:
+ * In this test a 1000 classes are loaded and unloaded in a loop.
+ * Class0 gets loaded which results in Class1 getting loaded and so on all
+ * the way uptill class1000.  The classes should be unloaded whenever a


nit: /uptill/up until/ or /up to/

dholmes-ora · 2021-11-24T05:15:34Z

test/hotspot/jtreg/vmTestbase/gc/gctests/LoadUnloadGC/LoadUnloadGC.java

+ * Class0 gets loaded which results in Class1 getting loaded and so on all
+ * the way uptill class1000.  The classes should be unloaded whenever a
+ * garbage collection takes place because their classloader is made unreachable
+ * at the end of the each loop iteration. The loop is repeated 1000 times.


nit: s/the each/each/

fisk · 2021-11-25T09:49:43Z

/integrate

openjdk · 2021-11-25T09:50:53Z

Going to push as commit 3034ae8.
Since your change was applied there have been 52 commits pushed to the master branch:

f0136ec: 8275687: runtime/CommandLine/PrintTouchedMethods test shouldn't catch RuntimeException
21e302a: 8270435: UT: MonitorUsedDeflationThresholdTest failed: did not find too_many string in output
a81e4fc: 8258117: jar tool sets the time stamp of module-info.class entries to the current time
26472bd: 8277811: ProblemList vmTestbase/nsk/jdi/TypeComponent/isSynthetic/issynthetic001/TestDescription.java
b5841ba: 8277806: 4 tools/jar failures per platform after JDK-8272728
e785f69: 8276124: Provide snippet support for properties files
96fe1d0: 8264605: vmTestbase/nsk/jvmti/SuspendThread/suspendthrd003/TestDescription.java failed with "agent_tools.cpp, 471: (foundThread = (jthread) jni_env->NewGlobalRef(foundThread)) != NULL"
077b2de: 8274161: Cleanup redundant casts in jdk.compiler
951247c: 8235876: Misleading warning message in java source-file mode
663e33d: 8272728: javac ignores any -J option in @argfiles silently
... and 42 more: https://git.openjdk.java.net/jdk/compare/3f847fe89a088d6921107ca887a7a1bace871bd6...master

Your commit was automatically rebased without conflicts.

openjdk · 2021-11-25T09:51:11Z

@fisk Pushed as commit 3034ae8.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

8277631: ZGC: CriticalMetaspaceAllocation asserts

ec93bed

openjdk bot added the rfr label Nov 23, 2021

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pliden approved these changes Nov 23, 2021

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ea65117

openjdk bot closed this Nov 25, 2021

openjdk bot added integrated and removed ready rfr labels Nov 25, 2021

8277631: ZGC: CriticalMetaspaceAllocation asserts #6520

8277631: ZGC: CriticalMetaspaceAllocation asserts #6520

fisk commented Nov 23, 2021 •

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8277631: ZGC: CriticalMetaspaceAllocation asserts #6520

8277631: ZGC: CriticalMetaspaceAllocation asserts #6520

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fisk commented Nov 23, 2021 • edited by openjdk[bot] bot

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