Author here! If you're running a Kubernetes cluster, I recommend you check `kubectl version` and see if you're running "Server Version: v1.36.[0,1,2]". If so, you may want to use the one-liner at the end of the article to check your "process_resident_memory_bytes" on each node, and consider restarting kubelet as a temporary workaround to tame the memory leak until v1.36.3 is released.
Can't help but feel this is one of the subtle traps hidden beneath the advice that contexts aren't supposed to be stored. I know it's not always that easy, of course.
Thanks. I know there's a `go vet` tool that's run as part of Kubernetes CI, and one of its checks is:
lostcancel: check cancel func returned by context.WithCancel is called
I'm not 100% sure why `go vet` didn't catch this issue, but storing the cancelFn in the struct is probably part of the reason. Any Go experts know if that's the case?
The cancel function escapes the function body, so static analysis can't detect it. There's another lint for that (containedctx), but I think it's off in K8s.
This is a serious tripping point with Go. There's no way to express: "this is a root context that I _want_ to store and only use to create derived contexts". Goroutines are also a source of problems, you can't easily say "I'm passing the ownership of this context to a goroutine".
I took a quick look at "containedctx" and it seems like for this case, it would almost be backwards: it would flag the (not-memory-leaking) struct-stored "status.ctx", but wouldn't flag when there is a stored "status.cancelFn" only (which resulted in the memory leak).
Author here! If you're running a Kubernetes cluster, I recommend you check `kubectl version` and see if you're running "Server Version: v1.36.[0,1,2]". If so, you may want to use the one-liner at the end of the article to check your "process_resident_memory_bytes" on each node, and consider restarting kubelet as a temporary workaround to tame the memory leak until v1.36.3 is released.
Nice find.
Can't help but feel this is one of the subtle traps hidden beneath the advice that contexts aren't supposed to be stored. I know it's not always that easy, of course.
Thanks. I know there's a `go vet` tool that's run as part of Kubernetes CI, and one of its checks is:
I'm not 100% sure why `go vet` didn't catch this issue, but storing the cancelFn in the struct is probably part of the reason. Any Go experts know if that's the case?The cancel function escapes the function body, so static analysis can't detect it. There's another lint for that (containedctx), but I think it's off in K8s.
This is a serious tripping point with Go. There's no way to express: "this is a root context that I _want_ to store and only use to create derived contexts". Goroutines are also a source of problems, you can't easily say "I'm passing the ownership of this context to a goroutine".
It does seem like a serious tripping point.
I took a quick look at "containedctx" and it seems like for this case, it would almost be backwards: it would flag the (not-memory-leaking) struct-stored "status.ctx", but wouldn't flag when there is a stored "status.cancelFn" only (which resulted in the memory leak).
Could Go implement a runtime leaked-context detector, like the data race detector? https://go.dev/doc/articles/race_detector
Very cool. It's often daunting to contribute to such a well-established and recognizable project, but this is exactly how it should work.
A good reason to health check the kubelet process and restart it when the checks fail.
What kind of health checks? In my case, the kubelet process was staying alive and responsive to queries, I believe due to:
With this score, the Linux OOM killer wouldn't touch it, but any of my Pods were fair game.Not all heroes wear capes! Well done