RFR: 8257746: Regression introduced with JDK-8250984 - memory might be null in some machines
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: public long getMemoryAndSwapFailCount() { if (!memory.isSwapEnabled()) { return getMemoryFailCount(); } return SubSystem.getLongValue(memory, "memory.memsw.failcnt"); } 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. ------------- Commit messages: - 8257746: Regression introduced with JDK-8250984 - memory might be null in some machines Changes: https://git.openjdk.java.net/jdk/pull/2269/files Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2269&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8257746 Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod Patch: https://git.openjdk.java.net/jdk/pull/2269.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/2269/head:pull/2269 PR: https://git.openjdk.java.net/jdk/pull/2269
On Wed, 27 Jan 2021 21:10:16 GMT, Poonam Bajaj <poonam@openjdk.org> wrote:
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:
public long getMemoryAndSwapFailCount() { if (!memory.isSwapEnabled()) { return getMemoryFailCount(); } return SubSystem.getLongValue(memory, "memory.memsw.failcnt"); }
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.
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? ------------- PR: https://git.openjdk.java.net/jdk/pull/2269
On Thu, 28 Jan 2021 14:36:36 GMT, Severin Gehwolf <sgehwolf@openjdk.org> wrote:
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?
I don't have access to the config. The issue was reported by a customer. ------------- PR: https://git.openjdk.java.net/jdk/pull/2269
On Thu, 28 Jan 2021 15:01:11 GMT, Poonam Bajaj <poonam@openjdk.org> wrote:
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?
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?
I don't have access to the config. The issue was reported by a customer.
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?
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?
I don't have access to the config. The issue was reported by a customer.
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." ------------- PR: https://git.openjdk.java.net/jdk/pull/2269
On Thu, 28 Jan 2021 16:00:36 GMT, Severin Gehwolf <sgehwolf@openjdk.org> wrote:
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?
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?
I don't have access to the config. The issue was reported by a customer.
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. private CgroupV1MemorySubSystemController memory; private void setMemorySubSystem(CgroupV1MemorySubSystemController memory) { this.memory = memory; } This memory instance variable could stay null if "memory" entry is not found while creating sub-system objects in createSubSystemController(). case "memory": subsystem.setMemorySubSystem(new CgroupV1MemorySubSystemController(mountentry[3], mountentry[4])); break; 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. ------------- PR: https://git.openjdk.java.net/jdk/pull/2269
On Thu, 28 Jan 2021 17:19:53 GMT, Poonam Bajaj <poonam@openjdk.org> wrote:
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?
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?
I don't have access to the config. The issue was reported by a customer.
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.
That would be helpful. A stack trace of the NPE would be good too.
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.
``` private CgroupV1MemorySubSystemController memory;
private void setMemorySubSystem(CgroupV1MemorySubSystemController memory) { this.memory = memory; } ```
This memory instance variable could stay null if "memory" entry is not found while creating sub-system objects in createSubSystemController().
``` case "memory": subsystem.setMemorySubSystem(new CgroupV1MemorySubSystemController(mountentry[3], mountentry[4])); break; ```
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.
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. ------------- PR: https://git.openjdk.java.net/jdk/pull/2269
On Wed, 27 Jan 2021 21:10:16 GMT, Poonam Bajaj <poonam@openjdk.org> wrote:
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:
public long getMemoryAndSwapFailCount() { if (!memory.isSwapEnabled()) { return getMemoryFailCount(); } return SubSystem.getLongValue(memory, "memory.memsw.failcnt"); }
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.
Changes look good! Thanks for doing this. Harold ------------- Marked as reviewed by hseigel (Reviewer). PR: https://git.openjdk.java.net/jdk/pull/2269
On Wed, 27 Jan 2021 21:10:16 GMT, Poonam Bajaj <poonam@openjdk.org> wrote:
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:
public long getMemoryAndSwapFailCount() { if (!memory.isSwapEnabled()) { return getMemoryFailCount(); } return SubSystem.getLongValue(memory, "memory.memsw.failcnt"); }
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.
This pull request has now been integrated. Changeset: abc4300d Author: Poonam Bajaj <poonam@openjdk.org> URL: https://git.openjdk.java.net/jdk/commit/abc4300d Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod 8257746: Regression introduced with JDK-8250984 - memory might be null in some machines Reviewed-by: hseigel ------------- PR: https://git.openjdk.java.net/jdk/pull/2269
participants (3)
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Harold Seigel
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Poonam Bajaj
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Severin Gehwolf