This patch enhances the BPF helpers by adding a kfunc to retrieve the cgroup v2 ID of a specific task, addressing a previous limitation where only bpf_task_get_cgroup1 was available for cgroup v1. The new kfunc is particularly useful for scenarios where obtaining the cgroup ID of a task other than the "current" one is necessary, which the existing bpf_get_current_cgroup_id helper cannot accommodate. A specific use case at Netflix involved the sched_switch tracepoint, where we had to get the cgroup IDs of both the previous and next tasks.
The bpf_task_get_cgroup_id kfunc returns a task's cgroup ID, correctly implementing RCU read locking and unlocking for safe data access, and leverages existing cgroup.h helpers to fetch the cgroup and its ID.
Signed-off-by: Jose Fernandez josef@netflix.com Reviewed-by: Tycho Andersen tycho@tycho.pizza --- kernel/bpf/helpers.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index a89587859571..8038b2bd3488 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -2266,6 +2266,27 @@ bpf_task_get_cgroup1(struct task_struct *task, int hierarchy_id) return NULL; return cgrp; } + +/** + * bpf_task_get_cgroup_id - Get the cgroup ID of a task. + * @task: The target task + * + * This function returns the ID of the task's default cgroup, primarily + * designed for use with cgroup v2. In cgroup v1, the concept of default + * cgroup varies by subsystem, and while this function will work with + * cgroup v1, it's recommended to use bpf_task_get_cgroup1 instead. + */ +__bpf_kfunc u64 bpf_task_get_cgroup_id(struct task_struct *task) +{ + struct cgroup *cgrp; + u64 cgrp_id; + + rcu_read_lock(); + cgrp = task_dfl_cgroup(task); + cgrp_id = cgroup_id(cgrp); + rcu_read_unlock(); + return cgrp_id; +} #endif /* CONFIG_CGROUPS */
/** @@ -2573,6 +2594,7 @@ BTF_ID_FLAGS(func, bpf_cgroup_ancestor, KF_ACQUIRE | KF_RCU | KF_RET_NULL) BTF_ID_FLAGS(func, bpf_cgroup_from_id, KF_ACQUIRE | KF_RET_NULL) BTF_ID_FLAGS(func, bpf_task_under_cgroup, KF_RCU) BTF_ID_FLAGS(func, bpf_task_get_cgroup1, KF_ACQUIRE | KF_RCU | KF_RET_NULL) +BTF_ID_FLAGS(func, bpf_task_get_cgroup_id, KF_RCU) #endif BTF_ID_FLAGS(func, bpf_task_from_pid, KF_ACQUIRE | KF_RET_NULL) BTF_ID_FLAGS(func, bpf_throw)