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8257746: Regression introduced with JDK-8250984 - memory might be null in some machines #2269
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…l in some machines
👋 Welcome back poonam! A progress list of the required criteria for merging this PR into |
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I'm curious: What config is this to actually trigger the NPE? How does /proc/self/mountinfo
, /proc/self/cgroup
and /proc/cgroups
look like?
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Changes look good! Thanks for doing this.
Harold
@poonamparhar 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:
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I don't have access to the config. The issue was reported by a customer. |
/integrate |
@poonamparhar Since your change was applied there have been 23 commits pushed to the
Your commit was automatically rebased without conflicts. Pushed as commit abc4300. 💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored. |
This isn't very satisfying, though. How can we be sure this issue isn't also present in the cgroup v2 code? Has this been tested? Surely, there was some stack trace reported by the customer or some sort of reproducer got provided. What was the reasoning that established this issue is present in JDK head and only in cgroups v1 code? My guess is that the issue got triggered via the OperatingSystemMXBean, but nothing to that effect has been noted here or in the bug. If I were to propose such a point fix, clearly, I'd have to provide some details what the actual problem is and explain why the fix is sufficient and covers all branches. All that got provided is: "But memory could be Null on some machines that have cgroup entries for CPU but not for memory." |
I can check with the customer if they could share their config. The cgroups v2 code was thoroughly examined and this problem does not exist in that code. cgroups v2 does not have a separate MemorySubSystemController as we have for c1 cgroups. An instance of the CgroupV1MemorySubSystemController is stored as a member in CgroupV1Subsystem.
This memory instance variable could stay null if "memory" entry is not found while creating sub-system objects in createSubSystemController().
This fix ensure that the memory instance is not null before invoking any method on it. Such problem does not exist in cgroups v2 code. |
That would be helpful. A stack trace of the NPE would be good too.
Right, but is this reasoning sound? Without knowing the code path triggering the problem and knowing something about the config can we really say? Depending on the config it might fail in some very different way on cgroups v2! On the other hand, knowing the config, might allow us to conclude it's an impossible config on cgroups v2 and we are done. |
Please review this simple change that adds null checks for memory in CgroupV1Subsystem.java.
Problem: After the backport of JDK-8250984, there are places where memory.isSwapEnabled() is called. For example:
But memory could be Null on some machines that have cgroup entries for CPU but not for memory. This would cause a NullPointerException when memory is accessed.
Fix: Add null checks for memory.
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$ git fetch https://git.openjdk.java.net/jdk pull/2269/head:pull/2269
$ git checkout pull/2269