cgns v3 #9452
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The bpf_cgroup_from_id kfunc relies on cgroup_get_from_id to obtain the cgroup corresponding to a given cgroup ID. This helper can be called in a lot of contexts where the current thread can be random. A recent example was its use in sched_ext's ops.tick(), to obtain the root cgroup pointer. Since the current task can be whatever random user space task preempted by the timer tick, this makes the behavior of the helper unreliable. Resolve this by refactoring cgroup_get_from_id to take a parameter to elide the cgroup_is_descendant check when root_cgns parameter is set to true. There is no compatibility breakage here, since changing the namespace against which the lookup is being done to the root cgroup namespace only permits a wider set of lookups to succeed now. The cgroup IDs across namespaces are globally unique, and thus don't need to be retranslated. Reported-by: Dan Schatzberg <[email protected]> Acked-by: Tejun Heo <[email protected]> Signed-off-by: Kumar Kartikeya Dwivedi <[email protected]>
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Make sure that we only switch the cgroup namespace and enter a new cgroup in a child process separate from test_progs, to not mess up the environment for subsequent tests. To remove this cgroup, we need to wait for the child to exit, and then rmdir its cgroup. If the read call fails, or waitpid succeeds, we know the child exited (read call would fail when the last pipe end is closed, otherwise waitpid waits until exit(2) is called). We then invoke a newly introduced remove_cgroup_pid() helper, that identifies cgroup path using the passed in pid of the now dead child, instead of using the current process pid (getpid()). Signed-off-by: Kumar Kartikeya Dwivedi <[email protected]>
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