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8287073: NPE from CgroupV2Subsystem.getInstance() #8803

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8287073: NPE from CgroupV2Subsystem.getInstance() #8803

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8287073: NPE from CgroupV2Subsystem.getInstance()
mkartashev May 20, 2022
932ff6d
Removed unnecessary null checks
mkartashev May 26, 2022
9e6c0f3
Made requested changes
mkartashev May 26, 2022
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2 changes: 1 addition & 1 deletion src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
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Looking at implementation of CgroupV2Subsystem.getInstance(...), it seems that it always returns != null ...

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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?

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@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;
}

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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.

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

} else {
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