Pull cgroup updates from Tejun Heo:

 - Last cycle deferred css teardown on cgroup removal until the cgroup
   depopulated, so a css is not taken offline while tasks can still
   reference it. Disabling a controller through cgroup.subtree_control
   still had the same problem. This reworks the deferral from per-cgroup
   to per-css so that path is covered too.

 - New RDMA controller monitoring files: rdma.peak for per-device peak
   usage and rdma.events / rdma.events.local for resource-limit
   exhaustion. The max-limit parser was rewritten, fixing two input
   parsing bugs.

 - cpuset: fix a sched-domain leak on the domain-rebuild failure path
   and skip a redundant hardwall ancestor scan on v2.

 - Misc: pair the remaining lockless cgroup.max.* reads with WRITE_ONCE,
   assorted selftest robustness fixes, and doc path corrections.

* tag 'cgroup-for-7.2' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup: (22 commits)
  cgroup: Migrate tasks to the root css when a controller is rebound
  docs: cgroup: Fix stale source file paths
  cgroup/cpuset: Free sched domains on rebuild guard failure
  cgroup: pair max limit READ_ONCE() with WRITE_ONCE()
  selftests/cgroup: enable memory controller in hugetlb memcg test
  cgroup/rdma: Drop unnecessary READ_ONCE() on event counters
  cgroup: Defer kill_css_finish() in cgroup_apply_control_disable()
  cgroup: Add per-subsys-css kill_css_finish deferral
  cgroup: Move populated counters to cgroup_subsys_state
  cgroup: Annotate unlocked nr_populated_* accesses with READ_ONCE/WRITE_ONCE
  cgroup: Inline cgroup_has_tasks() in cgroup.h
  cgroup/rdma: document rdma.peak, rdma.events and rdma.events.local
  cgroup/rdma: add rdma.events.local for per-cgroup allocation failure attribution
  cgroup/rdma: add rdma.events to track resource limit exhaustion
  cgroup/rdma: add rdma.peak for per-device peak usage tracking
  selftests/cgroup: check malloc return value in alloc_anon functions
  cgroup/cpuset: Skip hardwall ancestor scan in cpuset v2 in cpuset_current_node_allowed()
  selftests/cgroup: fix misleading debug message in test_cgfreezer_time_child
  selftests/cgroup: fix child process escaping to parent cleanup in test_cpucg_nice
  selftests/cgroup: Add NULL check after malloc in cgroup_util.c
  ...

cgroup_apply_control_disable() defers kill_css_finish() while a css is
still populated, relying on css_update_populated() to fire the deferred
kill once the populated count reaches zero.

This deadlocks when a controller is rebound out of a hierarchy. Mounting
an implicit_on_dfl controller such as perf_event as a v1 hierarchy steals
it off the default hierarchy, and rebind_subsystems() kills its
per-cgroup csses while they are still populated. The migration run in the
same step keeps the old css for a controller no longer in the hierarchy's
mask, so no task is migrated off the dying csses. Their populated count
never reaches zero, the deferred kill_css_finish() never fires, and the
next cgroup_lock_and_drain_offline() hangs forever under cgroup_mutex.

That migration is already a no-op pass over the rebound subtree. Add
cgroup_rebind_ss_mask so find_existing_css_set() resolves the leaving
controllers to the root css. Their tasks are migrated there, the
per-cgroup csses depopulate, and cgroup_apply_control_disable() kills
them synchronously. The deferral stays correct for the rmdir and
controller-disable paths it was meant for.

Fixes: 1dffd95575eb ("cgroup: Defer kill_css_finish() in cgroup_apply_control_disable()")
Reported-by: Mark Brown <broonie@kernel.org>
Closes: https://lore.kernel.org/all/41cd159c-54e5-45e0-81df-eaf36a6c028e@sirena.org.uk/
Reported-by: Bert Karwatzki <spasswolf@web.de>
Closes: https://lore.kernel.org/all/4e986b4ed7e16547805d54b6e67d09120bc4d2f2.camel@web.de/
Tested-by: Mark Brown <broonie@kernel.org>
Tested-by: Bert Karwatzki <spasswolf@web.de>
Signed-off-by: Tejun Heo <tj@kernel.org>

cgroup.max.descendants and cgroup.max.depth are shown through seq_file.
Their show callbacks read cgrp->max_descendants and cgrp->max_depth with
READ_ONCE(), respectively.

The corresponding write callbacks update the same scalar fields while
holding the cgroup lock, but the seq_file show path does not serialize
against those stores. This leaves the lockless show-side loads annotated
with READ_ONCE(), while the corresponding stores remain plain stores.

Use WRITE_ONCE() for the updates so the intended lockless access is marked
consistently on both sides. This does not change locking, ordering, or
user-visible semantics.

Assisted-by: OpenAI-Codex:gpt-5.5
Signed-off-by: Ren Tamura <ren.tamura.oss@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Same race shape as the rmdir path that 93618edf7538 ("cgroup: Defer css
percpu_ref kill on rmdir until cgroup is depopulated") fixed: a task past
exit_signals() whose cset subsys[ssid] still pins the disabled controller's
css can be touching subsys state while ->css_offline() runs. The earlier
patches in this series built up the per-subsys-css deferral machinery and
routed cgroup_destroy_locked() through it. Apply the same shape to
cgroup_apply_control_disable():

	kill_css_sync(css);
	if (!css_is_populated(css))
		kill_css_finish(css);

When the dying css is still populated, kill_css_finish() is deferred. The
walker in css_update_populated() fires kill_finish_work once the css's
hierarchical populated count drops to zero.

cgroup_lock_and_drain_offline()'s wait predicate switches from
percpu_ref_is_dying() to css_is_dying(). CSS_DYING is set by kill_css_sync()
and is a strict superset of percpu_ref_is_dying. Without this change, a +cpu
re-enable after a deferred -cpu disable would skip the drain (percpu_ref
isn't killed yet) and observe the still-CSS_DYING css through cgroup_css(),
treating it as live.

Signed-off-by: Tejun Heo <tj@kernel.org>

93618edf7538 ("cgroup: Defer css percpu_ref kill on rmdir until cgroup is
depopulated") deferred kill_css_finish() at the cgroup level: rmdir waits
for the entire cgroup's populated count to drop to zero, then fires
kill_css_finish() on every subsystem css at once. Replace that with
per-subsys-css deferral. Each subsystem css now tracks its own hierarchical
populated count and independently defers its kill_css_finish() until its own
subtree drains.

The rmdir-race fix carries through unchanged in shape. The dying css's
->css_offline() still waits until no PF_EXITING task references it, and v2's
cgroup-level machinery goes away.

cgroup_apply_control_disable() has the same race shape (PF_EXITING tasks
pinning a css whose ->css_offline() is about to run) and stays synchronous
here. This patch lays the groundwork for fixing it - per-cgroup waiting
can't gate one subsys css being killed while the rest of the cgroup stays
live, but per-css can.

Subtree-wide invariant preserved: a dying ancestor css stays populated
through nr_populated_children until every dying descendant's task drains, so
the walker fires the ancestor's kill_finish_work only after all descendants
have drained.

Add paired smp_mb()s in kill_css_sync() and css_update_populated() to fence
the StoreLoad on (CSS_DYING, populated counter), guaranteeing that either
the walker queues kill_finish_work or the caller fires synchronously.
cgroup_destroy_locked() was implicitly fenced by an unrelated css_set_lock
pair; cgroup_apply_control_disable() in the next patch is not.

Signed-off-by: Tejun Heo <tj@kernel.org>

Later patches replace the cgroup-level finish_destroy_work deferral added
by 93618edf7538 ("cgroup: Defer css percpu_ref kill on rmdir until cgroup
is depopulated") with a per-subsys-css deferral. That needs each subsystem
css to track its own populated count. Move the populated counters from
cgroup onto cgroup_subsys_state. cgroup->self is itself a
cgroup_subsys_state and self.parent walks the same chain as cgroup_parent(),
so cgroup_update_populated() generalizes to a single css_update_populated()
taking a css. The cgroup-side bookkeeping runs only when the walk started
from a self css.

Keep nr_populated_{domain,threaded}_children on cgroup. Both sum to
self.nr_populated_children, but staying as dedicated fields to allow readers
like cgroup_can_be_thread_root() unlocked access.

css_set_update_populated() also walks the per-subsys-css chain so each
subsystem css's hierarchical populated count is maintained. No reader
consumes those counts yet.

Signed-off-by: Tejun Heo <tj@kernel.org>

cgroup_update_populated() updates nr_populated_csets,
nr_populated_domain_children, and nr_populated_threaded_children under
css_set_lock, but cgroup_has_tasks(), cgroup_is_populated(), and
cgroup_can_be_thread_root() read them without holding it. Use
READ_ONCE/WRITE_ONCE.

Signed-off-by: Tejun Heo <tj@kernel.org>

cpuset reads cs->css.cgroup->nr_populated_csets directly in two places to
test whether a cgroup has tasks. cgroup.c already has a matching helper,
cgroup_has_tasks(). Move it to cgroup.h as static inline and use that
instead. This is to prepare for relocation of cgroup->nr_populated_csets. No
semantic change.

Signed-off-by: Tejun Heo <tj@kernel.org>

Pull cgroup fixes from Tejun Heo:

 - During v6.19, cgroup task unlink was moved from do_exit() to after the
   final task switch to satisfy a controller invariant. That left the kernel
   seeing tasks past exit_signals() longer than userspace expected, and
   several v7.0 follow-ups tried to bridge the gap by making rmdir wait for
   the kernel side. None held up.

   The latest is an A-A deadlock when rmdir is invoked by the reaper of
   zombies whose pidns teardown the rmdir itself is waiting on, which
   points at the synchronizing approach being fundamentally wrong.

   Take a different approach: drop the wait, leave rmdir's user-visible
   side returning as soon as cgroup.procs is empty, and defer the css
   percpu_ref kill that drives ->css_offline() until the cgroup is fully
   depopulated.

   Tagged for stable. Somewhat invasive but contained. The hope is that
   fixing forward sticks. If not, the fallback is to revert the entire
   chain and rework on the development branch.

   Note that this doesn't plug a pre-existing analogous race in
   cgroup_apply_control_disable() (controller disable via
   subtree_control). Not a regression. The development branch will do
   the more invasive restructuring needed for that.

 - Documentation update for cgroup-v1 charge-commit section that still
   referenced functions removed when the memcg hugetlb try-commit-cancel
   protocol was retired.

* tag 'cgroup-for-7.1-rc2-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  docs: cgroup-v1: Update charge-commit section
  cgroup: Defer css percpu_ref kill on rmdir until cgroup is depopulated

Pull sched_ext fixes from Tejun Heo:

 - Fix idle CPU selection returning prev_cpu outside the task's cpus_ptr
   when the BPF caller's allowed mask was wider. Stable backport.

 - Two opposite-direction gaps in scx_task_iter's cgroup-scoped mode
   versus the global mode:

    - Tasks past exit_signals() are filtered by the cgroup walk but kept
      by global. Sub-scheduler enable abort leaked __scx_init_task()
      state. Add a CSS_TASK_ITER_WITH_DEAD flag to cgroup's task
      iterator (scx_task_iter is its only user) and use it.

    - Tasks past sched_ext_dead() are still returned, tripping
      WARN_ON_ONCE() in callers or making them touch torn-down state.
      Mark and skip under the per-task rq lock.

* tag 'sched_ext-for-7.1-rc2-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext:
  sched_ext: idle: Recheck prev_cpu after narrowing allowed mask
  sched_ext: Skip past-sched_ext_dead() tasks in scx_task_iter_next_locked()
  cgroup, sched_ext: Include exiting tasks in cgroup iter