feat: Fixed eBPF Feature Detection #1443

dave-tucker · 2024-05-16T14:15:45Z

On working to migrate to cilium/ebpf I started to hit issues with
nil pointer dereferences that indicated that something odd was happening
between eBPF feature detection and metrics export.

I discovered that there were additional global variables in many of the
packages whose values are set before eBPF feature detection has
happened.

It appears that in these cases - through the various layers of
indirection - we may try and read/write metrics that do not exist
causing a nil pointer dereference.

There appear to be several places where we're accessing map keys
without checking they are nil - that will need to be fixed in a
follow up. This PR attempts to at least ensure that from the BPF
side that the keys we expect to exist, do actually exist in the
maps that matter.

eBPF feature detection how produces a bpf.SupportedMetrics
struct, which is now consumed in various places in the codebase
to ensure that the metrics we're exporting match those supported
by the eBPF exporter.

vimalk78 · 2024-05-16T17:28:24Z

pls share the NPE, and steps to reproduce

dave-tucker · 2024-05-16T18:49:47Z

NPE:

goroutine 71 [running]:
github.com/sustainable-computing-io/kepler/pkg/collector/stats/types.(*UInt64StatCollection).SumAllAggrValues(0x16d0[40](https://github.com/sustainable-computing-io/kepler/actions/runs/9114066283/job/25057276989?pr=1438#step:11:41)0?)
	/workspace/pkg/collector/stats/types/types.go:144 +0x16
github.com/sustainable-computing-io/kepler/pkg/metrics/utils.CollectResUtil(0x16d3460?, {0x179f7e0?, 0xc0000e81c0?}, {0x18f5588, 0xd}, {0x1b67f28, 0xc000066368})
	/workspace/pkg/metrics/utils/utils.go:1[41](https://github.com/sustainable-computing-io/kepler/actions/runs/9114066283/job/25057276989?pr=1438#step:11:42) +0x6ed
github.com/sustainable-computing-io/kepler/pkg/metrics/utils.CollectResUtilizationMetrics(0x1?, {0x179f7e0, 0xc0000e81c0}, 0xc0029d8180?, 0x0)
	/workspace/pkg/metrics/utils/utils.go:48 +0xc5
github.com/sustainable-computing-io/kepler/pkg/metrics/container.(*collector).Collect(0xc0025f8ed0, 0xc000061f60?)
	/workspace/pkg/metrics/container/metrics.go:105 +0xd8
github.com/prometheus/client_golang/prometheus.(*Registry).Gather.func1()
	/workspace/vendor/github.com/prometheus/client_golang/prometheus/registry.go:[45](https://github.com/sustainable-computing-io/kepler/actions/runs/9114066283/job/25057276989?pr=1438#step:11:46)5 +0x102
created by github.com/prometheus/client_golang/prometheus.(*Registry).Gather in goroutine 1
	/workspace/vendor/github.com/prometheus/client_golang/prometheus/registry.go:5[47](https://github.com/sustainable-computing-io/kepler/actions/runs/9114066283/job/25057276989?pr=1438#step:11:48) +0xbab

utils.CollectResUtil is the offending function, where it's assuming that a hashmap entry exists - which it may not.

As far as I can tell the NPE was caused by the following chain of events:

CollectResUtilizationMetrics gets called via the prometheus collector
It iterates over several arrays of constants e.g consts.SCMetricNames and consts.IRQMetricNames and then calls down into utils.CollectResUtil
- NOTE: config.IsIRQCounterMetricsEnabled() gets checked before it tries to do anything with the IRQ metrics
CollectResUtil takes an interface {} argument (in this case operating on a ContainerStats object)
It indexes directly into ContainerStats.ResourceUsage["bpf_net_tx_irq"] without checking it exists

In which circumstances would "bpf_net_tx_irq" not exist then?

We can trace NewContainerStats -> NewStats and see that the ResourceUsage map is populated from a global variable called AvailableBPFSWCounters
InitAvailableParamAndMetrics sets the global ☝️ after the bpf programs are loaded - it was empty beforehand

So the only way this can occur is when config.IsIRQCounterMetricsEnabled() == true BUT we don't have any of the IRQ keys in the array of supported eBPF software counters. I'll continue to debug here to see why that's happening.

I'm not sure what I managed to do with the cilium/ebpf port and with this patch to make that issue worse... but there is definitely something fishy happening 🐟 Still trying to untangle this to find out what's going on.

vimalk78 · 2024-05-16T18:56:58Z

NPE:

on which commit? does main + this PR reproduce it? or main + cillium PR ?

vimalk78 · 2024-05-16T18:59:50Z

NPE:

on which commit? does main + this PR reproduce it? or main + cillium PR ?

got it. main + cillium PR

dave-tucker · 2024-05-16T19:00:52Z

main + cillium PR ?

That will reproduce it (for now). I'm only able to reproduce it in CI so using this PR to help debug it.

dave-tucker · 2024-05-16T20:29:45Z

This PR is ready to go.

As for the root cause, I ended up hooking up a debugger and I found out that the issue was that in #1413 I'd forgotten to attach one of the perf_events - a software event called (config.TaskClock). I've fixed this and I'll push into CI tomorrow to see if it resolves the NPE.

EDIT: It still doesn't explain why the bpf_irq_net_tx counter would NPE.

Either way the issue is basically because we have 2 competing definitions of "what's supported by ebpf". This PR fixes that.

pkg/bpf/exporter.go

On working to migrate to cilium/ebpf I started to hit issues with nil pointer dereferences that indicated that something odd was happening between eBPF feature detection and metrics export. I discovered that there were additional global variables in many of the packages whose values are set before eBPF feature detection has happened. It appears that in these cases - through the various layers of indirection - we may try and read/write metrics that do not exist causing a nil pointer dereference. There appear to be several places where we're accessing map keys without checking they are nil - that will need to be fixed in a follow up. This PR attempts to at least ensure that from the BPF side that the keys we expect to exist, do actually exist in the maps that matter. eBPF feature detection how produces a bpf.SupportedMetrics struct, which is now consumed in various places in the codebase to ensure that the metrics we're exporting match those supported by the eBPF exporter. Signed-off-by: Dave Tucker <dave@dtucker.co.uk>

sthaha · 2024-05-17T21:13:26Z

pkg/bpf/exporter.go

 		}
 	}

+	if !config.ExposeHardwareCounterMetrics {
+		klog.Infof("Hardware counter metrics are disabled")


nit: How about we Warn?

sthaha

lgtm

dave-tucker mentioned this pull request May 16, 2024

chore(pkg/bpf): Replace libbpfgo with cilium/ebpf #1438

Draft

dave-tucker marked this pull request as draft May 16, 2024 15:13

dave-tucker force-pushed the hcmetrics branch 2 times, most recently from e5a2371 to e37a3c2 Compare May 16, 2024 16:49

dave-tucker changed the title ~~chore: Remove IsHCMetricsEnabled~~ feat: Fixed eBPF Feature Detection May 16, 2024

dave-tucker force-pushed the hcmetrics branch from 7e4408b to d8ed196 Compare May 16, 2024 17:50

dave-tucker force-pushed the hcmetrics branch 3 times, most recently from 859120e to a0ebf8c Compare May 16, 2024 19:35

dave-tucker marked this pull request as ready for review May 16, 2024 19:36