Chen Ridong ded4d207a3 cgroup: split cgroup_destroy_wq into 3 workqueues ... [ Upstream commit 79f919a89c9d06816dbdbbd168fa41d27411a7f9 ] 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: 334c3679ec ("cgroup: reimplement rebind_subsystems() using cgroup_apply_control() and friends") Reported-by: Gao Yingjie <gaoyingjie@uniontech.com> Signed-off-by: Chen Ridong <chenridong@huawei.com> Suggested-by: Teju Heo <tj@kernel.org> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>		2025-09-25 11:13:42 +02:00
..
cgroup-internal.h
cgroup-v1.c
cgroup.c	cgroup: split cgroup_destroy_wq into 3 workqueues	2025-09-25 11:13:42 +02:00
cpuset-internal.h	cgroup/cpuset: Don't allow creation of local partition over a remote one	2025-05-02 07:59:21 +02:00
cpuset-v1.c
cpuset.c	cgroup/cpuset: Fix a partition error with CPU hotplug	2025-08-28 16:31:11 +02:00
debug.c
freezer.c
legacy_freezer.c	Revert "cgroup_freezer: cgroup_freezing: Check if not frozen"	2025-07-24 08:56:35 +02:00
Makefile
misc.c
namespace.c
pids.c
rdma.c
rstat.c	cgroup/rstat: avoid disabling irqs for O(num_cpu)	2025-05-29 11:02:10 +02:00