8303908: Add missing check in VTMS_transition_disable_for_all() for suspend mode by pchilano · Pull Request #12956 · openjdk/jdk

pchilano · 2023-03-09T18:55:06Z

Please review this small fix. A suspender is a JvmtiVTMSTransitionDisabler monopolist, meaning VTMS_transition_disable_for_all() should not return while there is any active jvmtiVTMSTransitionDisabler. The code though is checking for active "all-disablers" but it's missing the check for active "single disablers".
I attached a simple reproducer to the bug which I used to test the patch. Not sure if it was worth adding a test so the patch contains just the fix.

Thanks,
Patricio

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JDK-8303908: Add missing check in VTMS_transition_disable_for_all() for suspend mode

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Serguei Spitsyn (@sspitsyn - Reviewer)
David Holmes (@dholmes-ora - Reviewer)

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bridgekeeper · 2023-03-09T18:56:13Z

👋 Welcome back pchilanomate! 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 · 2023-03-09T18:58:21Z

@pchilano The following labels will be automatically applied to this pull request:

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serviceability

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mlbridge · 2023-03-09T19:19:23Z

Webrevs

00: Full (c4352913)

sspitsyn

This looks good.
Thank you for catching and taking care about it!
Serguei

openjdk · 2023-03-10T03:52:43Z

@pchilano 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:

8303908: Add missing check in VTMS_transition_disable_for_all() for suspend mode

Reviewed-by: sspitsyn, 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 40 new commits pushed to the master branch:

c313e1a: 8303922: build-test-lib target is broken
fbc76c2: 8304017: ProblemList com/sun/jdi/InvokeHangTest.java on windows-x64 in vthread mode
a06426a: 8274400: HotSpot Style Guide should permit use of alignof
98a7a60: 8303863: RISC-V: TestArrayStructs.java fails after JDK-8303604
0a4d54f: 8299779: Test tools/jpackage/share/jdk/jpackage/tests/MainClassTest.java timed out
2116928: 8303900: Rename BitMap search functions
d7f4221: 8304005: ProblemList serviceability/AsyncGetCallTrace/MyPackage/ASGCTBaseTest.java on linux-x64 in Xcomp mode
94de0a7: 8302513: remove sun.awt.util.IdentityLinkedList
bf16b5b: 8303937: Corrupted heap dumps due to missing retries for os::write()
6f54eda: 8299088: ClassLoader::defineClass2 throws OOME but JNI exception pending thrown by getUTF
... and 30 more: https://git.openjdk.org/jdk/compare/1e9942aa112edca33f964db127df6c9ce41e86ff...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.

dholmes-ora · 2023-03-10T04:34:13Z

src/hotspot/share/prims/jvmtiThreadState.cpp

  MonitorLocker ml(JvmtiVTMSTransition_lock);
  java_lang_Thread::dec_VTMS_transition_disable_count(vth());
  Atomic::dec(&_VTMS_transition_disable_for_one_count);
-  if (_VTMS_transition_disable_for_one_count == 0 || _is_SR) {


Sorry I don't understand why this _is_SR check was removed. I admit I can't really figure out what this field means anyway, but there is nothing in the issue description that suggests this also needs changing - and it is now different to VTMS_transition_enable_for_all.

A JvmtiVTMSTransitionDisabler instance that is a "single disabler" only blocks other virtual threads trying to transition or JvmtiVTMSTransitionDisabler monopolists. Both of them will check for _VTMS_transition_disable_for_one_count (the JvmtiVTMSTransitionDisabler monopolist was missing that check) so just checking when that counter is zero is enough. In fact, for a "single disabler" _is_SR is always false so that check wasn't doing anything. Yes, this is not actually needed for the fix, but when looking at which condition we use to wait and which one to notify I caught this, sorry for not explaining that part.

And looking closer at VTMS_transition_enable_for_all() now I see the check for _is_SR is not doing anything too, because if _VTMS_transition_disable_for_all_count was not zero after the decrement then this can't be a JvmtiVTMSTransitionDisabler monopolist, i.e _is_SR will be false. When a monopolist is running all other "disable all" JvmtiVTMSTransitionDisabler instances if any will be waiting in the first "while (_SR_mode)" loop in VTMS_transition_disable_for_all(), so _VTMS_transition_disable_for_all_count will be one through the monopolist run. So this should be an assert after the decrement: assert(!_is_SR || _VTMS_transition_disable_for_all_count == 0, "").

Thanks for clarifying - I was puzzled by the way is_SR was being used.

pchilano · 2023-03-10T17:00:12Z

This looks good. Thank you for catching and taking care about it! Serguei

Thanks for the review Serguei!

dholmes-ora

Looks good. Thanks.

pchilano · 2023-03-13T15:45:51Z

Looks good. Thanks.

Thanks for the review David!

pchilano · 2023-03-13T20:13:33Z

/integrate

openjdk · 2023-03-13T20:15:30Z

Going to push as commit a8f662e.
Since your change was applied there have been 56 commits pushed to the master branch:

5685107: 8302491: NoClassDefFoundError omits the original cause of an error
671a452: 8303606: Memory leaks in Arguments::parse_each_vm_init_arg
a95bc7a: 8294974: Convert jdk.jshell/jdk.jshell.execution.LocalExecutionControl to use the Classfile API to instrument classes
f835aaa: 8300727: java/awt/List/ListGarbageCollectionTest/AwtListGarbageCollectionTest.java failed with "List wasn't garbage collected"
466ffeb: 8303965: java.net.http.HttpClient should reset the stream if response headers contain malformed header fields
431e702: 8303213: Avoid AtomicReference in TextComponentPrintable
4cf4c59: 8303824: Parallel: Use more strict card table API
8e41bf2: 8303238: Create generalizations for existing LShift ideal transforms
805a4e6: 8303883: Confusing parameter name in G1UpdateRemSetTrackingBeforeRebuild::distribute_marked_bytes
25e7ac2: 8294966: Convert jdk.jartool/sun.tools.jar.FingerPrint to use the ClassFile API to parse JAR entries
... and 46 more: https://git.openjdk.org/jdk/compare/1e9942aa112edca33f964db127df6c9ce41e86ff...master

Your commit was automatically rebased without conflicts.

openjdk · 2023-03-13T20:15:44Z

@pchilano Pushed as commit a8f662e.

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

v1

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openjdk bot added serviceability serviceability-dev@openjdk.org hotspot hotspot-dev@openjdk.org labels Mar 9, 2023

pchilano marked this pull request as ready for review March 9, 2023 19:14

openjdk bot added the rfr Pull request is ready for review label Mar 9, 2023

sspitsyn approved these changes Mar 10, 2023

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openjdk bot added the ready Pull request is ready to be integrated label Mar 10, 2023

dholmes-ora reviewed Mar 10, 2023

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dholmes-ora approved these changes Mar 13, 2023

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openjdk bot closed this Mar 13, 2023

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