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cgroup: Move cgrp_dead_ task+iwork into its own struct

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cgrp_dead_tasks and cgrp_dead_tasks_iwork are independent per-CPU variables
and are independently accessed via a this_cpu_ptr().

Having a custom struct with those two members makes it possible to have only
one per-CPU accessor and access the second member via an offset. This makes
the code a bit more compact and is a micro-optimization.

Besides that, it allows cgrp_dead_tasks_iwork_fn() to access the list
pointer via the passed iwork pointer. This not only eliminates the
this_cpu_ptr() but also makes it possible to be invoked on a different CPU.
This does not happen as of today but might if I can flush the irq_work items
from another CPU during CPU-hotplug events.

Create struct cgroup_dead with the per-CPU variables as members. Access the
struct with a per-CPU accessor and use container_of() in the irq_work
callback.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Sebastian Andrzej Siewior 2026-09-11 12:19:00 +02:00 committed by Tejun Heo
parent c367ce5b31
commit de99a40c54
1 changed files with 15 additions and 8 deletions
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23
kernel/cgroup/cgroup.c
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@ -7212,15 +7212,19 @@ static void do_cgroup_task_dead(struct task_struct *tsk)
* the cgroup and task_struct can be pinned indefinitely. Bounce through lazy
* irq_work to allow batching while ensuring timely completion.
*/
static DEFINE_PER_CPU(struct llist_head, cgrp_dead_tasks);
static DEFINE_PER_CPU(struct irq_work, cgrp_dead_tasks_iwork);
struct cgroup_dead {
struct irq_work iwork;
struct llist_head tasks;
};
static DEFINE_PER_CPU(struct cgroup_dead, cgroup_dead);
static void cgrp_dead_tasks_iwork_fn(struct irq_work *iwork)
{
struct cgroup_dead *cgrp_dead = container_of(iwork, struct cgroup_dead, iwork);
struct llist_node *lnode;
struct task_struct *task, *next;
lnode = llist_del_all(this_cpu_ptr(&cgrp_dead_tasks));
lnode = llist_del_all(&cgrp_dead->tasks);
llist_for_each_entry_safe(task, next, lnode, cg_dead_lnode) {
do_cgroup_task_dead(task);
put_task_struct(task);
@ -7232,17 +7236,20 @@ static void __init cgroup_rt_init(void)
int cpu;
for_each_possible_cpu(cpu) {
init_llist_head(per_cpu_ptr(&cgrp_dead_tasks, cpu));
per_cpu(cgrp_dead_tasks_iwork, cpu) =
IRQ_WORK_INIT_LAZY(cgrp_dead_tasks_iwork_fn);
struct cgroup_dead *cgrp_dead = per_cpu_ptr(&cgroup_dead, cpu);
init_llist_head(&cgrp_dead->tasks);
cgrp_dead->iwork = IRQ_WORK_INIT_LAZY(cgrp_dead_tasks_iwork_fn);
}
}
void cgroup_task_dead(struct task_struct *task)
{
struct cgroup_dead *cgrp_dead = this_cpu_ptr(&cgroup_dead);
get_task_struct(task);
llist_add(&task->cg_dead_lnode, this_cpu_ptr(&cgrp_dead_tasks));
irq_work_queue(this_cpu_ptr(&cgrp_dead_tasks_iwork));
llist_add(&task->cg_dead_lnode, &cgrp_dead->tasks);
irq_work_queue(&cgrp_dead->iwork);
}
#else /* CONFIG_PREEMPT_RT */
static void __init cgroup_rt_init(void) {}