linux/kernel/sched/core_sched.c

// SPDX-License-Identifier: GPL-2.0-only

#include "sched.h"

/*
 * A simple wrapper around refcount. An allocated sched_core_cookie's
 * address is used to compute the cookie of the task.
 */
struct sched_core_cookie {
	refcount_t refcnt;
};

unsigned long sched_core_alloc_cookie(void)
{
	struct sched_core_cookie *ck = kmalloc(sizeof(*ck), GFP_KERNEL);
	if (!ck)
		return 0;

	refcount_set(&ck->refcnt, 1);
	sched_core_get();

	return (unsigned long)ck;
}

void sched_core_put_cookie(unsigned long cookie)
{
	struct sched_core_cookie *ptr = (void *)cookie;

	if (ptr && refcount_dec_and_test(&ptr->refcnt)) {
		kfree(ptr);
		sched_core_put();
	}
}

unsigned long sched_core_get_cookie(unsigned long cookie)
{
	struct sched_core_cookie *ptr = (void *)cookie;

	if (ptr)
		refcount_inc(&ptr->refcnt);

	return cookie;
}

/*
 * sched_core_update_cookie - replace the cookie on a task
 * @p: the task to update
 * @cookie: the new cookie
 *
 * Effectively exchange the task cookie; caller is responsible for lifetimes on
 * both ends.
 *
 * Returns: the old cookie
 */
unsigned long sched_core_update_cookie(struct task_struct *p, unsigned long cookie)
{
	unsigned long old_cookie;
	struct rq_flags rf;
	struct rq *rq;
	bool enqueued;

	rq = task_rq_lock(p, &rf);

	/*
	 * Since creating a cookie implies sched_core_get(), and we cannot set
	 * a cookie until after we've created it, similarly, we cannot destroy
	 * a cookie until after we've removed it, we must have core scheduling
	 * enabled here.
	 */
	SCHED_WARN_ON((p->core_cookie || cookie) && !sched_core_enabled(rq));

	enqueued = sched_core_enqueued(p);
	if (enqueued)
		sched_core_dequeue(rq, p);

	old_cookie = p->core_cookie;
	p->core_cookie = cookie;

	if (enqueued)
		sched_core_enqueue(rq, p);

	/*
	 * If task is currently running, it may not be compatible anymore after
	 * the cookie change, so enter the scheduler on its CPU to schedule it
	 * away.
	 */
	if (task_running(rq, p))
		resched_curr(rq);

	task_rq_unlock(rq, p, &rf);

	return old_cookie;
}

static unsigned long sched_core_clone_cookie(struct task_struct *p)
{
	unsigned long cookie, flags;

	raw_spin_lock_irqsave(&p->pi_lock, flags);
	cookie = sched_core_get_cookie(p->core_cookie);
	raw_spin_unlock_irqrestore(&p->pi_lock, flags);

	return cookie;
}

void sched_core_fork(struct task_struct *p)
{
	RB_CLEAR_NODE(&p->core_node);
	p->core_cookie = sched_core_clone_cookie(current);
}

void sched_core_free(struct task_struct *p)
{
	sched_core_put_cookie(p->core_cookie);
}