linux/kernel/cgroup/cgroup.c, branch v6.17

cgroup/psi: Set of->priv to NULL upon file release

2025-08-22T17:47:43Z

Setting of->priv to NULL when the file is released enables earlier bug detection. This allows potential bugs to manifest as NULL pointer dereferences rather than use-after-free errors[1], which are generally more difficult to diagnose. [1] https://lore.kernel.org/cgroups/38ef3ff9-b380-44f0-9315-8b3714b0948d@huaweicloud.com/T/#m8a3b3f88f0ff3da5925d342e90043394f8b2091b Signed-off-by: Chen Ridong Signed-off-by: Tejun Heo

cgroup: split cgroup_destroy_wq into 3 workqueues

2025-08-22T17:44:11Z

A hung task can occur during [1] LTP cgroup testing when repeatedly mounting/unmounting perf_event and net_prio controllers with systemd.unified_cgroup_hierarchy=1. The hang manifests in cgroup_lock_and_drain_offline() during root destruction. Related case: cgroup_fj_function_perf_event cgroup_fj_function.sh perf_event cgroup_fj_function_net_prio cgroup_fj_function.sh net_prio Call Trace: cgroup_lock_and_drain_offline+0x14c/0x1e8 cgroup_destroy_root+0x3c/0x2c0 css_free_rwork_fn+0x248/0x338 process_one_work+0x16c/0x3b8 worker_thread+0x22c/0x3b0 kthread+0xec/0x100 ret_from_fork+0x10/0x20 Root Cause: CPU0 CPU1 mount perf_event umount net_prio cgroup1_get_tree cgroup_kill_sb rebind_subsystems // root destruction enqueues // cgroup_destroy_wq // kill all perf_event css // one perf_event css A is dying // css A offline enqueues cgroup_destroy_wq // root destruction will be executed first css_free_rwork_fn cgroup_destroy_root cgroup_lock_and_drain_offline // some perf descendants are dying // cgroup_destroy_wq max_active = 1 // waiting for css A to die Problem scenario: 1. CPU0 mounts perf_event (rebind_subsystems) 2. CPU1 unmounts net_prio (cgroup_kill_sb), queuing root destruction work 3. A dying perf_event CSS gets queued for offline after root destruction 4. Root destruction waits for offline completion, but offline work is blocked behind root destruction in cgroup_destroy_wq (max_active=1) Solution: Split cgroup_destroy_wq into three dedicated workqueues: cgroup_offline_wq – Handles CSS offline operations cgroup_release_wq – Manages resource release cgroup_free_wq – Performs final memory deallocation This separation eliminates blocking in the CSS free path while waiting for offline operations to complete. [1] https://github.com/linux-test-project/ltp/blob/master/runtest/controllers Fixes: 334c3679ec4b ("cgroup: reimplement rebind_subsystems() using cgroup_apply_control() and friends") Reported-by: Gao Yingjie Signed-off-by: Chen Ridong Suggested-by: Teju Heo Signed-off-by: Tejun Heo

cgroup: Add bpf prog revisions to struct cgroup_bpf

2025-06-09T23:17:11Z

One of key items in mprog API is revision for prog list. The revision number will be increased if the prog list changed, e.g., attach, detach or replace. Add 'revisions' field to struct cgroup_bpf, representing revisions for all cgroup related attachment types. The initial revision value is set to 1, the same as kernel mprog implementations. Signed-off-by: Yonghong Song Signed-off-by: Andrii Nakryiko Acked-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20250606163136.2428732-1-yonghong.song@linux.dev

Merge tag 'cgroup-for-6.16' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

2025-05-28T03:59:53Z

Pull cgroup updates from Tejun Heo: - cgroup rstat shared the tracking tree across all controllers with the rationale being that a cgroup which is using one resource is likely to be using other resources at the same time (ie. if something is allocating memory, it's probably consuming CPU cycles). However, this turned out to not scale very well especially with memcg using rstat for internal operations which made memcg stat read and flush patterns substantially different from other controllers. JP Kobryn split the rstat tree per controller. - cgroup BPF support was hooking into cgroup init/exit paths directly. Convert them to use a notifier chain instead so that other usages can be added easily. The two of the patches which implement this are mislabeled as belonging to sched_ext instead of cgroup. Sorry. - Relatively minor cpuset updates - Documentation updates * tag 'cgroup-for-6.16' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup: (23 commits) sched_ext: Convert cgroup BPF support to use cgroup_lifetime_notifier sched_ext: Introduce cgroup_lifetime_notifier cgroup: Minor reorganization of cgroup_create() cgroup, docs: cpu controller's interaction with various scheduling policies cgroup, docs: convert space indentation to tab indentation cgroup: avoid per-cpu allocation of size zero rstat cpu locks cgroup, docs: be specific about bandwidth control of rt processes cgroup: document the rstat per-cpu initialization cgroup: helper for checking rstat participation of css cgroup: use subsystem-specific rstat locks to avoid contention cgroup: use separate rstat trees for each subsystem cgroup: compare css to cgroup::self in helper for distingushing css cgroup: warn on rstat usage by early init subsystems cgroup/cpuset: drop useless cpumask_empty() in compute_effective_exclusive_cpumask() cgroup/rstat: Improve cgroup_rstat_push_children() documentation cgroup: fix goto ordering in cgroup_init() cgroup: fix pointer check in css_rstat_init() cgroup/cpuset: Add warnings to catch inconsistency in exclusive CPUs cgroup/cpuset: Fix obsolete comment in cpuset_css_offline() cgroup/cpuset: Always use cpu_active_mask ...

sched_ext: Convert cgroup BPF support to use cgroup_lifetime_notifier

2025-05-22T19:20:19Z

Replace explicit cgroup_bpf_inherit/offline() calls from cgroup creation/destruction paths with notification callback registered on cgroup_lifetime_notifier. Signed-off-by: Tejun Heo

sched_ext: Introduce cgroup_lifetime_notifier

2025-05-22T19:20:11Z

Other subsystems may make use of the cgroup hierarchy with the cgroup_bpf support being one such example. For such a feature, it's useful to be able to hook into cgroup creation and destruction paths to perform feature-specific initializations and cleanups. Add cgroup_lifetime_notifier which generates CGROUP_LIFETIME_ONLINE and CGROUP_LIFETIME_OFFLINE events whenever cgroups are created and destroyed, respectively. The next patch will convert cgroup_bpf to use the new notifier and other uses are planned. Signed-off-by: Tejun Heo

cgroup: Minor reorganization of cgroup_create()

2025-05-22T19:19:57Z

cgroup_bpf init and exit handling will be moved to a notifier chain. In prepartion, reorganize cgroup_create() a bit so that the new cgroup is fully initialized before any outside changes are made. - cgrp->ancestors[] initialization and the hierarchical nr_descendants and nr_frozen_descendants updates were in the same loop. Separate them out and do the former earlier and do the latter later. - Relocate cgroup_bpf_inherit() call so that it's after all cgroup initializations are complete. No visible behavior changes expected. Signed-off-by: Tejun Heo

cgroup: use subsystem-specific rstat locks to avoid contention

2025-05-19T20:29:42Z

It is possible to eliminate contention between subsystems when updating/flushing stats by using subsystem-specific locks. Let the existing rstat locks be dedicated to the cgroup base stats and rename them to reflect that. Add similar locks to the cgroup_subsys struct for use with individual subsystems. Lock initialization is done in the new function ss_rstat_init(ss) which replaces cgroup_rstat_boot(void). If NULL is passed to this function, the global base stat locks will be initialized. Otherwise, the subsystem locks will be initialized. Change the existing lock helper functions to accept a reference to a css. Then within these functions, conditionally select the appropriate locks based on the subsystem affiliation of the given css. Add helper functions for this selection routine to avoid repeated code. Signed-off-by: JP Kobryn Signed-off-by: Tejun Heo

cgroup: use separate rstat trees for each subsystem

2025-05-19T20:28:59Z

Different subsystems may call cgroup_rstat_updated() within the same cgroup, resulting in a tree of pending updates from multiple subsystems. When one of these subsystems is flushed via cgroup_rstat_flushed(), all other subsystems with pending updates on the tree will also be flushed. Change the paradigm of having a single rstat tree for all subsystems to having separate trees for each subsystem. This separation allows for subsystems to perform flushes without the side effects of other subsystems. As an example, flushing the cpu stats will no longer cause the memory stats to be flushed and vice versa. In order to achieve subsystem-specific trees, change the tree node type from cgroup to cgroup_subsys_state pointer. Then remove those pointers from the cgroup and instead place them on the css. Finally, change update/flush functions to make use of the different node type (css). These changes allow a specific subsystem to be associated with an update or flush. Separate rstat trees will now exist for each unique subsystem. Since updating/flushing will now be done at the subsystem level, there is no longer a need to keep track of updated css nodes at the cgroup level. The list management of these nodes done within the cgroup (rstat_css_list and related) has been removed accordingly. Conditional guards for checking validity of a given css were placed within css_rstat_updated/flush() to prevent undefined behavior occuring from kfunc usage in bpf programs. Guards were also placed within css_rstat_init/exit() in order to help consolidate calls to them. At call sites for all four functions, the existing guards were removed. Signed-off-by: JP Kobryn Signed-off-by: Tejun Heo

cgroup: compare css to cgroup::self in helper for distingushing css

2025-05-19T20:21:24Z

Adjust the implementation of css_is_cgroup() so that it compares the given css to cgroup::self. Rename the function to css_is_self() in order to reflect that. Change the existing css->ss NULL check to a warning in the true branch. Finally, adjust call sites to use the new function name. Signed-off-by: JP Kobryn Signed-off-by: Tejun Heo