cgroup_attach_task(9)

💖 cgroup_attach_task — Kernel API Manual energy ✨

okay bestie, we're diving into the kernel API manual today — yes, that manual — and this one's about cgroup_attach_task(9), aka the function that scoops up a task (or a whole entire threadgroup, no big deal) and drops it into a cgroup. cgroups are the main character of resource management, and this is the little glue function that does the actual yeeting. let's go 🎀

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🌸 NAME 🌸

cgroup_attach_task — attaches a task or a whole threadgroup to a cgroup. that's the whole vibe. two-for-one. iconic.

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✨ SYNOPSIS ✨

int cgroup_attach_task (struct cgroup *dst_cgrp , struct task_struct
*leader , bool threadgroup );

like, look at that signature. three args, one int coming back at you. slay.

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🦋 ARGUMENTS 🦋

• dst_cgrp — the cgroup you're attaching to. the destination. the home. the place where the task is gonna live now 💅
• leader — the task itself, or, if you're doing the group thing, the leader of the threadgroup that's getting attached. leader behaviour, fr.
• threadgroup — the big question: are we attaching the whole threadgroup? yes or no, that's the bool, that's the vibe check right there 🫶

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💜 DESCRIPTION 💜

here's the whole description, and it's short and spicy: Call holding cgroup_mutex and cgroup_threadgroup_rwsem.

that's it. that's the whole thing. so like — when you call this, you gotta be holding both of those locks. cgroup_mutex and cgroup_threadgroup_rwsem. no cap, both of them. don't come at this function empty-handed 🙈

⚠️ for real though, this is the kind of note you do not skip. the page says call it holding those locks, so you hold those locks. periodt.

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👑 SEE ALSO 👑

Kernel file ./kernel/cgroup/cgroup.c — that's where the source lives, go say hi 🧚

and now, the friendship bracelet of cross-references. every single one, in order, exactly as the page lists them:

cgroup_ssid_enabled(9), cgroup_on_dfl(9), cgroup_e_css_by_mask(9), cgroup_e_css(9), cgroup_get_e_css(9), __cgroup_task_count(9), cgroup_task_count(9), for_each_css(9), do_each_subsys_mask(9), css_set_populated(9), css_update_populated(9), css_set_update_populated(9), css_set_move_task(9), compare_css_sets(9), find_existing_css_set(9), allocate_cgrp_cset_links(9), link_css_set(9), find_css_set(9), cgroup_file_mode(9), cgroup_calc_subtree_ss_mask(9),

cgroup_kn_unlock(9), cgroup_kn_lock_live(9), css_clear_dir(9), css_populate_dir(9), cgroup_attach_lock(9), cgroup_attach_unlock(9), cgroup_migrate_add_task(9), cgroup_taskset_first(9), cgroup_taskset_next(9), cgroup_migrate_execute(9), cgroup_migrate_vet_dst(9), cgroup_migrate_finish(9), cgroup_migrate_add_src(9), cgroup_migrate_prepare_dst(9), cgroup_migrate(9), cgroup_update_dfl_csses(9),

cgroup_lock_and_drain_offline(9), cgroup_save_control(9), cgroup_propagate_control(9), cgroup_restore_control(9), cgroup_apply_control_enable(9), cgroup_apply_control_disable(9), cgroup_apply_control(9), cgroup_finalize_control(9), cgroup_enable_threaded(9), cgroup_tryget_css(9), cgroup_addrm_files(9), cgroup_rm_cftypes(9), cgroup_add_cftypes(9), cgroup_add_dfl_cftypes(9), cgroup_add_legacy_cftypes(9), cgroup_file_notify(9), cgroup_file_show(9),

css_next_child(9), css_next_descendant_pre(9), css_rightmost_descendant(9), css_next_descendant_post(9), css_has_online_children(9), css_task_iter_advance_css_set(9), css_task_iter_start(9), css_task_iter_next(9), css_task_iter_end(9), css_create(9), kill_css_sync(9), kill_css_finish(9), cgroup_destroy_locked(9), cgroup_init_early(9), cgroup_init(9), cgroup_fork(9), cgroup_v1v2_get_from_file(9), cgroup_get_from_file(9),

cgroup_css_set_fork(9), cgroup_css_set_put_fork(9), cgroup_can_fork(9), cgroup_cancel_fork(9), cgroup_post_fork(9), cgroup_task_exit(9), css_tryget_online_from_dir(9), css_from_id(9), cgroup_get_from_path(9), cgroup_v1v2_get_from_fd(9), cgroup_get_from_fd(9), cgroup_parse_float(9)

that's the whole list, ate and left no crumbs 🔥

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💀 also quick note that this page is very "trust me bro" about its DESCRIPTION — one line, two locks, that's your lot. but honestly? sometimes less is more and this is one of those times. lowkey obsessed.

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and that's the page, bestie 🌈 this one's from the ./kernel/cgroup source and it's dated October 2026, filed under cgroup_attach_task(9). go forth, hold your locks, attach your tasks 💖✨🎀