8287073: NPE from CgroupV2Subsystem.getInstance() #8803

mkartashev · 2022-05-20T08:34:58Z

Following the logic from the comment directly above the changed line, since it doesn't matter which controller we pick, pick any available controller instead of the one called "memory" specifically. This way we are guarded against getting null as anyController, which is being immediately passed down to CgroupV2Subsystem.getInstance() that is unprepared to accept null values.

It is also worth noting that the previous checks (such as that at line 89) make sure that there exist at least one controller in the map.

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Issue

JDK-8287073: NPE from CgroupV2Subsystem.getInstance()

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Vladimir Kempik (@VladimirKempik - Committer) ⚠️ Review applies to f17af433
Ioi Lam (@iklam - Reviewer)

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bridgekeeper · 2022-05-20T08:36:10Z

👋 Welcome back mkartashev! 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 · 2022-05-20T08:38:08Z

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

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mlbridge · 2022-05-20T08:42:18Z

Webrevs

VladimirKempik

Can some reviewer take a look at this please ?
This seems to be addressing rare corner issue.

plevart · 2022-05-25T14:39:42Z

src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java

@@ -108,7 +108,7 @@ static CgroupMetrics create() {
        Map<String, CgroupInfo> infos = result.getInfos();
        if (result.isCgroupV2()) {
            // For unified it doesn't matter which controller we pick.
-            CgroupInfo anyController = infos.get(MEMORY_CTRL);
+            CgroupInfo anyController = infos.values().iterator().next();
            CgroupSubsystem subsystem = CgroupV2Subsystem.getInstance(anyController);
            return subsystem != null ? new CgroupMetrics(subsystem) : null;


Looking at implementation of CgroupV2Subsystem.getInstance(...), it seems that it always returns != null ...

CgroupV1Subsystem.getInstance(...) also claims that it never returns null, but has a code-path that actually returns null (when there is no active controller). Is this a possible outcome?

@plevart Are you asking about the reason for the crash or about the changes?
If it's the former, then I believe that the crash comes not from getInstance() returning null, but from further down the stack because null is being passed to getInstance(). I could be wrong in interpreting the report, though.

If the question's about the changes, then those are restricted to CgroupV2, so I'm not sure how CgroupV1Subsystem.getInstance(...) returning null is related. FWIW, I also don't think we are going to get here if there are no active controllers. There's this code a few lines above:

if (!result.isAnyControllersEnabled()) { return null; }

I was just contemplating the code around the change as it appears to have unnecessary checks which result in dead code. From the point of fixing just this concrete NPE, they are irrelevant. So while this code might benefit from cleanup, perhaps this PR is not the place to do it. Perhaps it is a matter of another issue and PR.

@plevart I think I now understand what you meant and removed the unnecessary checks. Please, have a look.

iklam · 2022-05-26T15:23:35Z

src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java

        } else {
            CgroupV1Subsystem subsystem = CgroupV1Subsystem.getInstance(infos);
-            return subsystem != null ? new CgroupV1MetricsImpl(subsystem) : null;
+            return new CgroupV1MetricsImpl(subsystem);


This shouldn't be changed because the current implementation of CgroupV1Subsystem.getInstance(infos) has a path that returns null.

Maybe that's impossible, because when we call CgroupV1Subsystem.getInstance, we must have at least one v1 subsystem in infos. However, that's not related to this issue. Please fix that in a separate RFE. For example, CgroupV1Subsystem.getInstance(infos) can be changed to throw an exception instead if return null.

Fine by me; done.

iklam · 2022-05-26T15:25:32Z

src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java

            CgroupSubsystem subsystem = CgroupV2Subsystem.getInstance(anyController);
-            return subsystem != null ? new CgroupMetrics(subsystem) : null;
+            return new CgroupMetrics(subsystem);


Should add Objects.requireNonNull(anyController) and Objects.requireNonNull(subsystem).

I added the first, but not the second as that looks like an overkill; see the definition of the constructor:

CgroupMetrics(CgroupSubsystem subsystem) { this.subsystem = Objects.requireNonNull(subsystem); }

openjdk · 2022-05-26T18:19:08Z

@mkartashev 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:

8287073: NPE from CgroupV2Subsystem.getInstance()

Reviewed-by: vkempik, iklam

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At the time when this comment was updated there had been 97 new commits pushed to the master branch:

176bb23: 8287200: Test java/lang/management/ThreadMXBean/VirtualThreadDeadlocks.java timed out after JDK-8287103
ec97da9: 8287352: DockerTestUtils::execute shows incorrect elapsed time
140419f: 8286058: AArch64: clarify types of calls
6a33974: 8286737: Test vmTestbase/gc/gctests/WeakReference/weak006/weak006.java fails: Last soft reference has not been cleared
295be6f: 8287285: Avoid redundant HashMap.containsKey call in java.util.zip.ZipFile.Source.get
7cb368b: 8286709: (fc) FileChannel/FileChannelImpl cleanup
7eb1559: 8286045: Use ForceGC for cleaner test cases
e44465d: 8287336: GHA: Workflows break on patch versions
c10749a: 8287187: Utilize HashMap.newHashMap() in CLDRConverter
f235955: 8287246: DSAKeyValue should check for missing params instead of relying on KeyFactory provider
... and 87 more: https://git.openjdk.java.net/jdk/compare/d5d19f52ceb1430104b12a42c78489f42477a9b0...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.

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➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

mkartashev · 2022-05-27T08:31:54Z

/integrate

openjdk · 2022-05-27T08:34:11Z

@mkartashev
Your change (at version 9e6c0f3) is now ready to be sponsored by a Committer.

iklam · 2022-05-30T06:16:35Z

I tested the patch in our CI pipeline. All container tests passed.
/integrate

iklam · 2022-05-30T06:16:51Z

/sponsor

openjdk · 2022-05-30T06:18:07Z

@iklam Only the author (@mkartashev) is allowed to issue the integrate command. As this pull request is ready to be sponsored, and you are an eligible sponsor, did you mean to issue the /sponsor command?

openjdk · 2022-05-30T06:18:54Z

Going to push as commit 744b822.
Since your change was applied there have been 114 commits pushed to the master branch:

5848a60: 8286093: java/awt/geom/Path2D/UnitTest.java failed with "RuntimeException: 2D bounds too small"
3d2d039: 8287440: Typo in package-info.java of java.util.random
36350bf: 8287484: JFR: Seal RecordedObject
a6e2e22: 8285008: JFR: jdk/jfr/jmx/streaming/TestClose.java failed with "Exception: Expected repository to be empty"
2c461ac: 8287492: ProblemList compiler/jvmci/errors/TestInvalidDebugInfo.java
6634037: 8287362: FieldAccessWatch testcase failed on AIX platform
410a25d: 8286562: GCC 12 reports some compiler warnings
ed8e8ac: 8284400: Improve XPath exception handling
d3e781d: 8287223: C1: Inlining attempt through MH::invokeBasic() with null receiver
0df4748: 8287463: JFR: Disable TestDevNull.java on Windows
... and 104 more: https://git.openjdk.java.net/jdk/compare/d5d19f52ceb1430104b12a42c78489f42477a9b0...master

Your commit was automatically rebased without conflicts.

openjdk · 2022-05-30T06:19:11Z

@iklam @mkartashev Pushed as commit 744b822.

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

8287073: NPE from CgroupV2Subsystem.getInstance()

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VladimirKempik approved these changes May 25, 2022

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plevart reviewed May 25, 2022

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8287073: NPE from CgroupV2Subsystem.getInstance() #8803

8287073: NPE from CgroupV2Subsystem.getInstance() #8803

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8287073: NPE from CgroupV2Subsystem.getInstance() #8803

8287073: NPE from CgroupV2Subsystem.getInstance() #8803

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