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cgroup: avoid the unnecessary list_add(dying_tasks) in cgroup_exit()

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cgroup_exit() needs to do this only if the exiting task is a leader and it
is not the last live thread.  The patch doesn't use delay_group_leader(),
atomic_read(signal->live) matches the code css_task_iter_advance() more.

cgroup_release() can now check list_empty(task->cg_list) before it takes
css_set_lock and calls ss_set_skip_task_iters().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Oleg Nesterov 2024-06-17 16:31:52 +02:00 committed by Tejun Heo
parent 1805c1729f
commit 6fe960147e
1 changed files with 9 additions and 5 deletions
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14
kernel/cgroup/cgroup.c
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@ -6701,8 +6701,10 @@ void cgroup_exit(struct task_struct *tsk)
WARN_ON_ONCE(list_empty(&tsk->cg_list));
cset = task_css_set(tsk);
css_set_move_task(tsk, cset, NULL, false);
list_add_tail(&tsk->cg_list, &cset->dying_tasks);
cset->nr_tasks--;
/* matches the signal->live check in css_task_iter_advance() */
if (thread_group_leader(tsk) && atomic_read(&tsk->signal->live))
list_add_tail(&tsk->cg_list, &cset->dying_tasks);
if (dl_task(tsk))
dec_dl_tasks_cs(tsk);
@ -6729,10 +6731,12 @@ void cgroup_release(struct task_struct *task)
ss->release(task);
} while_each_subsys_mask();
spin_lock_irq(&css_set_lock);
css_set_skip_task_iters(task_css_set(task), task);
list_del_init(&task->cg_list);
spin_unlock_irq(&css_set_lock);
if (!list_empty(&task->cg_list)) {
spin_lock_irq(&css_set_lock);
css_set_skip_task_iters(task_css_set(task), task);
list_del_init(&task->cg_list);
spin_unlock_irq(&css_set_lock);
}
}
void cgroup_free(struct task_struct *task)