fix (cgroups): already dead edge case #3325
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Certain kubernetes version make use of short lived cgroups for various tasks (for example log rotation). These cgroups will generate events and a very quick cgroup_rmdir event. As such, many related events to the cgroup will attempt to query its directory through the recursive path and not find it. Commit adds a "Dead" field to the cgroup info to indicate a cgroup which has already been removed. Various logical sections can refer to it if its relevant to them, and more importantly, additional queries will not be attempted. Bonus: optimize away additional Stat syscall in containers by returning the directory ctime in cgroup.GetCgroupPath.
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yanivagman
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Jul 19, 2023
| @@ -137,7 +137,7 @@ func (p *Controller) processCgroupMkdir(args []trace.Argument) error { | |||
| if err != nil { | |||
| return errfmt.WrapError(err) | |||
| } | |||
| if info.Container.ContainerId == "" { | |||
| if info.Container.ContainerId == "" && !info.Dead { | |||
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Can this ever happen?
It means that we get mkdir event after rmdir event, doesn't it?
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It does, and it was the original indicator for the error (although it was on a tracee v0.11.1 installation).
This can happen because it's a race between userspace and ebpf. The entry can be deleted either here OR in the cgroup_rmdir program.
I guess this would also require a misorder in events received, so this doesn't fully resolve the case, but the result here is only an annoying (otherwise harmless) error log.
yanivagman
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Jul 19, 2023
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Fix #3324
@rafaeldtinoco I want to backport this to v0.16.0 branch if that's ok with you.