cgroup_migrate_add_src(9)

💅 cgroup_migrate_add_src — from the Kernel API Manual ✨

okay so bestie, buckle up, because we're doing kernel cgroup migration today and honestly it's giving main character energy 🎀

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🌸 NAME 🌸

cgroup_migrate_add_src — add a migration source css_set 💖

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✨ SYNOPSIS ✨

void cgroup_migrate_add_src (struct css_set *src_cset , struct cgroup
*dst_cgrp , struct cgroup_mgctx *mgctx );

like literally the whole signature, no cap, keep it exactly like that 🫶

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🦋 ARGUMENTS 🦋

• src_cset — the source css_set you're adding, bestie. this is the one being pinned ✨
• dst_cgrp — the destination cgroup, aka where everybody's headed 💫
• mgctx — the migration context, the group chat of this whole operation fr fr

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🌈 DESCRIPTION 🌈

so here's the vibe: the tasks that belong to src_cset are about to be migrated over to dst_cgrp. dramatic, i know 😭 what this function does is pin src_cset and add it to mgctx->src_csets — and like, that list should later get cleaned up by cgroup_migrate_finish. don't forget the cleanup bestie, that's the whole point 🙈

now, the iconic part 👑 — this function may be called without holding cgroup_threadgroup_rwsem, even if the target is a process. yes, even then. and like, threads may be created and destroyed the whole time, but as long as cgroup_mutex is not dropped, no new css_set can be put into play, and the preloaded css_sets are guaranteed to cover all migrations. periodt. 💅

lowkey important: the safety here is entirely on cgroup_mutex staying put. drop it and the guarantee walks out the door 💀

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🎀 SEE ALSO 🎀

kernel file ./kernel/cgroup/cgroup.c, plus the whole friend group:

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_prepare_dst(9), cgroup_migrate(9), cgroup_attach_task(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)

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and that's the whole thing, bestie 🧚 this lil page lives at ./kernel/cgroup, dated October 2026, and it's literally titled cgroup_migrate_add_src(9). mwah 💋✨🍓