cgroup1 delete: proceed to the next subsystem when a cgroup is not found #296
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The Delete method checks for running processes within each subsystem, before deleting the cgroup from it. On certain systems, there are cases when removing a cgroup from one subsystem, also removes it from others. For example, removing a cgroup from net_cls subsystem also removes the cgroup from net_prio. This is because both net_cls and net_prio have a symlink to 'net_cls,net_prio'. This is also true for cpu and cpuacct. This change handles the above case, when a query to get cgroup processes within a subsystem returns a fs.ErrNotExist. In such a case, we move to the next subsystem, instead of erroring out of Delete() immediately. This ensures that the cgroup is deleted from all subsystems that have it. Signed-off-by: Anuj Singh <singholt@amazon.com>
Signed-off-by: Anuj Singh <singholt@amazon.com>
singholt
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thanks for reviewing Phil! It looks like I may need another review, perhaps @kzys ? I'd appreciate if you could take a look 😄 |
dcantah
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Jun 19, 2023
This was referenced Jun 29, 2023
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Signed-off-by: Anuj Singh singholt@amazon.com
The cgroup1 Delete method checks for running processes within each subsystem, before deleting the cgroup from it.
I noticed that there are cases when removing a cgroup from one subsystem, also removes it from others.
For example, on Amazon Linux (kernel 4.14), removing a cgroup from
net_clssubsystem also removes the cgroup fromnet_prio. This is because bothnet_clsandnet_priohave a symlink to a common dirnet_cls, net_prio. Similarly, removing a cgroup fromcpualso removes it from thecpuacctsubsystem, because of a symlink tocpu,cpuacct.In such a case the Delete() errors out with an error like
Sample code: https://gist.github.com/singholt/2a600802c0f74c8acdacd247760dc291 that fails on the Delete() without this fix but passes with it.
This change handles the above case, when a query to get cgroup processes within a subsystem returns a
fs.ErrNotExist. In such a case, we move to the next subsystem, instead of erroring out of the Delete() immediately. This ensures that the cgroup is deleted from all subsystems that have it.As per cgroups v1 documentation, since files in a cgroup directory cannot and need not be removed, it is safe to assume that if
cgroup.procsdoesn't exist for a cgroup (within a subsystem), the cgroup has been removed from the subsystem.This PR has two commits - first addressing the problem above, with the unit test updated and second, just fixing a typo.