lwn.git/kernel/cgroup/cgroup.c, branch docs-mw

Merge tag 'mm-stable-2026-04-18-02-14' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2026-04-19T15:01:17+00:00

Pull more MM updates from Andrew Morton: - "Eliminate Dying Memory Cgroup" (Qi Zheng and Muchun Song) Address the longstanding "dying memcg problem". A situation wherein a no-longer-used memory control group will hang around for an extended period pointlessly consuming memory - "fix unexpected type conversions and potential overflows" (Qi Zheng) Fix a couple of potential 32-bit/64-bit issues which were identified during review of the "Eliminate Dying Memory Cgroup" series - "kho: history: track previous kernel version and kexec boot count" (Breno Leitao) Use Kexec Handover (KHO) to pass the previous kernel's version string and the number of kexec reboots since the last cold boot to the next kernel, and print it at boot time - "liveupdate: prevent double preservation" (Pasha Tatashin) Teach LUO to avoid managing the same file across different active sessions - "liveupdate: Fix module unloading and unregister API" (Pasha Tatashin) Address an issue with how LUO handles module reference counting and unregistration during module unloading - "zswap pool per-CPU acomp_ctx simplifications" (Kanchana Sridhar) Simplify and clean up the zswap crypto compression handling and improve the lifecycle management of zswap pool's per-CPU acomp_ctx resources - "mm/damon/core: fix damon_call()/damos_walk() vs kdmond exit race" (SeongJae Park) Address unlikely but possible leaks and deadlocks in damon_call() and damon_walk() - "mm/damon/core: validate damos_quota_goal->nid" (SeongJae Park) Fix a couple of root-only wild pointer dereferences - "Docs/admin-guide/mm/damon: warn commit_inputs vs other params race" (SeongJae Park) Update the DAMON documentation to warn operators about potential races which can occur if the commit_inputs parameter is altered at the wrong time - "Minor hmm_test fixes and cleanups" (Alistair Popple) Bugfixes and a cleanup for the HMM kernel selftests - "Modify memfd_luo code" (Chenghao Duan) Cleanups, simplifications and speedups to the memfd_lou code - "mm, kvm: allow uffd support in guest_memfd" (Mike Rapoport) Support for userfaultfd in guest_memfd - "selftests/mm: skip several tests when thp is not available" (Chunyu Hu) Fix several issues in the selftests code which were causing breakage when the tests were run on CONFIG_THP=n kernels - "mm/mprotect: micro-optimization work" (Pedro Falcato) A couple of nice speedups for mprotect() - "MAINTAINERS: update KHO and LIVE UPDATE entries" (Pratyush Yadav) Document upcoming changes in the maintenance of KHO, LUO, memfd_luo, kexec, crash, kdump and probably other kexec-based things - they are being moved out of mm.git and into a new git tree * tag 'mm-stable-2026-04-18-02-14' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (121 commits) MAINTAINERS: add page cache reviewer mm/vmscan: avoid false-positive -Wuninitialized warning MAINTAINERS: update Dave's kdump reviewer email address MAINTAINERS: drop include/linux/liveupdate from LIVE UPDATE MAINTAINERS: drop include/linux/kho/abi/ from KHO MAINTAINERS: update KHO and LIVE UPDATE maintainers MAINTAINERS: update kexec/kdump maintainers entries mm/migrate_device: remove dead migration entry check in migrate_vma_collect_huge_pmd() selftests: mm: skip charge_reserved_hugetlb without killall userfaultfd: allow registration of ranges below mmap_min_addr mm/vmstat: fix vmstat_shepherd double-scheduling vmstat_update mm/hugetlb: fix early boot crash on parameters without '=' separator zram: reject unrecognized type= values in recompress_store() docs: proc: document ProtectionKey in smaps mm/mprotect: special-case small folios when applying permissions mm/mprotect: move softleaf code out of the main function mm: remove '!root_reclaim' checking in should_abort_scan() mm/sparse: fix comment for section map alignment mm/page_io: use sio->len for PSWPIN accounting in sio_read_complete() selftests/mm: transhuge_stress: skip the test when thp not available ...

mm: memcontrol: prepare for reparenting non-hierarchical stats

2026-04-18T07:10:47+00:00

To resolve the dying memcg issue, we need to reparent LRU folios of child memcg to its parent memcg. This could cause problems for non-hierarchical stats. As Yosry Ahmed pointed out: In short, if memory is charged to a dying cgroup at the time of reparenting, when the memory gets uncharged the stats updates will occur at the parent. This will update both hierarchical and non-hierarchical stats of the parent, which would corrupt the parent's non-hierarchical stats (because those counters were never incremented when the memory was charged). Now we have the following two types of non-hierarchical stats, and they are only used in CONFIG_MEMCG_V1: a. memcg->vmstats->state_local[i] b. pn->lruvec_stats->state_local[i] To ensure that these non-hierarchical stats work properly, we need to reparent these non-hierarchical stats after reparenting LRU folios. To this end, this commit makes the following preparations: 1. implement reparent_state_local() to reparent non-hierarchical stats 2. make css_killed_work_fn() to be called in rcu work, and implement get_non_dying_memcg_start() and get_non_dying_memcg_end() to avoid race between mod_memcg_state()/mod_memcg_lruvec_state() and reparent_state_local() Link: https://lore.kernel.org/e862995c45a7101a541284b6ebee5e5c32c89066.1772711148.git.zhengqi.arch@bytedance.com Co-developed-by: Yosry Ahmed Signed-off-by: Yosry Ahmed Signed-off-by: Qi Zheng Acked-by: Shakeel Butt Cc: Allen Pais Cc: Axel Rasmussen Cc: Baoquan He Cc: Chengming Zhou Cc: Chen Ridong Cc: David Hildenbrand Cc: Hamza Mahfooz Cc: Harry Yoo Cc: Hugh Dickins Cc: Imran Khan Cc: Johannes Weiner Cc: Kamalesh Babulal Cc: Lance Yang Cc: Liam Howlett Cc: Lorenzo Stoakes (Oracle) Cc: Michal Hocko Cc: Michal Koutný Cc: Mike Rapoport Cc: Muchun Song Cc: Muchun Song Cc: Nhat Pham Cc: Roman Gushchin Cc: Suren Baghdasaryan Cc: Usama Arif Cc: Vlastimil Babka Cc: Wei Xu Cc: Yuanchu Xie Cc: Zi Yan Signed-off-by: Andrew Morton

Merge tag 'cgroup-for-7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

2026-04-15T17:18:49+00:00

Pull cgroup updates from Tejun Heo: - cgroup_file_notify() locking converted from a global lock to per-cgroup_file spinlock with a lockless fast-path when no notification is needed - Misc changes including exposing cgroup helpers for sched_ext and minor fixes * tag 'cgroup-for-7.1' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup: cgroup/rdma: fix swapped arguments in pr_warn() format string cgroup/dmem: remove region parameter from dmemcg_parse_limit cgroup: replace global cgroup_file_kn_lock with per-cgroup_file lock cgroup: add lockless fast-path checks to cgroup_file_notify() cgroup: reduce cgroup_file_kn_lock hold time in cgroup_file_notify() cgroup: Expose some cgroup helpers

cgroup: Fix cgroup_drain_dying() testing the wrong condition

2026-03-26T00:08:04+00:00

cgroup_drain_dying() was using cgroup_is_populated() to test whether there are dying tasks to wait for. cgroup_is_populated() tests nr_populated_csets, nr_populated_domain_children and nr_populated_threaded_children, but cgroup_drain_dying() only needs to care about this cgroup's own tasks - whether there are children is cgroup_destroy_locked()'s concern. This caused hangs during shutdown. When systemd tried to rmdir a cgroup that had no direct tasks but had a populated child, cgroup_drain_dying() would enter its wait loop because cgroup_is_populated() was true from nr_populated_domain_children. The task iterator found nothing to wait for, yet the populated state never cleared because it was driven by live tasks in the child cgroup. Fix it by using cgroup_has_tasks() which only tests nr_populated_csets. v3: Fix cgroup_is_populated() -> cgroup_has_tasks() (Sebastian). v2: https://lore.kernel.org/r/20260323200205.1063629-1-tj@kernel.org Reported-by: Sebastian Andrzej Siewior Fixes: 1b164b876c36 ("cgroup: Wait for dying tasks to leave on rmdir") Signed-off-by: Tejun Heo Tested-by: Sebastian Andrzej Siewior

cgroup: Wait for dying tasks to leave on rmdir

2026-03-24T20:21:40+00:00

a72f73c4dd9b ("cgroup: Don't expose dead tasks in cgroup") hid PF_EXITING tasks from cgroup.procs so that systemd doesn't see tasks that have already been reaped via waitpid(). However, the populated counter (nr_populated_csets) is only decremented when the task later passes through cgroup_task_dead() in finish_task_switch(). This means cgroup.procs can appear empty while the cgroup is still populated, causing rmdir to fail with -EBUSY. Fix this by making cgroup_rmdir() wait for dying tasks to fully leave. If the cgroup is populated but all remaining tasks have PF_EXITING set (the task iterator returns none due to the existing filter), wait for a kick from cgroup_task_dead() and retry. The wait is brief as tasks are removed from the cgroup's css_set between PF_EXITING assertion in do_exit() and cgroup_task_dead() in finish_task_switch(). v2: cgroup_is_populated() true to false transition happens under css_set_lock not cgroup_mutex, so retest under css_set_lock before sleeping to avoid missed wakeups (Sebastian). Fixes: a72f73c4dd9b ("cgroup: Don't expose dead tasks in cgroup") Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-lkp/202603222104.2c81684e-lkp@intel.com Reported-by: Sebastian Andrzej Siewior Signed-off-by: Tejun Heo Reviewed-by: Sebastian Andrzej Siewior Cc: Bert Karwatzki Cc: Michal Koutny Cc: cgroups@vger.kernel.org

cgroup: replace global cgroup_file_kn_lock with per-cgroup_file lock

2026-03-11T22:16:21+00:00

Replace the global cgroup_file_kn_lock with a per-cgroup_file spinlock to eliminate cross-cgroup contention as it is not really protecting data shared between different cgroups. The lock is initialized in cgroup_add_file() alongside timer_setup(). No lock acquisition is needed during initialization since the cgroup directory is being populated under cgroup_mutex and no concurrent accessors exist at that point. Reported-by: Jakub Kicinski Signed-off-by: Shakeel Butt Signed-off-by: Tejun Heo

cgroup: add lockless fast-path checks to cgroup_file_notify()

2026-03-11T22:16:21+00:00

Add lockless checks before acquiring cgroup_file_kn_lock: 1. READ_ONCE(cfile->kn) NULL check to skip torn-down files. 2. READ_ONCE(cfile->notified_at) rate-limit check to skip when within the notification interval. If within the interval, arm the deferred timer via timer_reduce() and confirm it is pending before returning -- if the timer fired in between, fall through to the lock path so the notification is not lost. Both checks have safe error directions -- a stale read can only cause unnecessary lock acquisition, never a missed notification. The critical section is simplified to just taking a kernfs_get() reference and updating notified_at. Annotate cfile->kn and cfile->notified_at write sites with WRITE_ONCE() to pair with the lockless readers. Reported-by: Jakub Kicinski Signed-off-by: Shakeel Butt Signed-off-by: Tejun Heo

cgroup: reduce cgroup_file_kn_lock hold time in cgroup_file_notify()

2026-03-11T22:16:21+00:00

cgroup_file_notify() calls kernfs_notify() while holding the global cgroup_file_kn_lock. kernfs_notify() does non-trivial work including wake_up_interruptible() and acquisition of a second global spinlock (kernfs_notify_lock), inflating the hold time. Take a kernfs_get() reference under the lock and call kernfs_notify() after dropping it, following the pattern from cgroup_file_show(). Reported-by: Jakub Kicinski Signed-off-by: Shakeel Butt Signed-off-by: Tejun Heo

cgroup: Don't expose dead tasks in cgroup

2026-03-06T22:43:25+00:00

Once a task exits it has its state set to TASK_DEAD and then it is removed from the cgroup it belonged to. The last step happens on the task gets out of its last schedule() invocation and is delayed on PREEMPT_RT due to locking constraints. As a result it is possible to receive a pid via waitpid() of a task which is still listed in cgroup.procs for the cgroup it belonged to. This is something that systemd does not expect and as a result it waits for its exit until a time out occurs. This can also be reproduced on !PREEMPT_RT kernel with a significant delay in do_exit() after exit_notify(). Hide the task from the output which have PF_EXITING set which is done before the parent is notified. Keeping zombies with live threads shouldn't break anything (suggested by Tejun). Reported-by: Bert Karwatzki Closes: https://lore.kernel.org/all/20260219164648.3014-1-spasswolf@web.de/ Tested-by: Bert Karwatzki Fixes: 9311e6c29b34 ("cgroup: Fix sleeping from invalid context warning on PREEMPT_RT") Cc: stable@vger.kernel.org # v6.19+ Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Tejun Heo

cgroup: Expose some cgroup helpers

2026-03-06T04:15:58+00:00

Expose the following through cgroup.h: - cgroup_on_dfl() - cgroup_is_dead() - cgroup_for_each_live_child() - cgroup_for_each_live_descendant_pre() - cgroup_for_each_live_descendant_post() Until now, these didn't need to be exposed because controllers only cared about the css hierarchy. The planned sched_ext hierarchical scheduler support will be based on the default cgroup hierarchy, which is in line with the existing BPF cgroup support, and thus needs these exposed. Signed-off-by: Tejun Heo