linux/io_uring/napi.c

// SPDX-License-Identifier: GPL-2.0

#include "io_uring.h"
#include "napi.h"

#ifdef CONFIG_NET_RX_BUSY_POLL

/* Timeout for cleanout of stale entries. */
#define NAPI_TIMEOUT		(60 * SEC_CONVERSION)

struct io_napi_entry {
	unsigned int		napi_id;
	struct list_head	list;

	unsigned long		timeout;
	struct hlist_node	node;

	struct rcu_head		rcu;
};

static struct io_napi_entry *io_napi_hash_find(struct hlist_head *hash_list,
					       unsigned int napi_id)
{
	struct io_napi_entry *e;

	hlist_for_each_entry_rcu(e, hash_list, node) {
		if (e->napi_id != napi_id)
			continue;
		return e;
	}

	return NULL;
}

static inline ktime_t net_to_ktime(unsigned long t)
{
	/* napi approximating usecs, reverse busy_loop_current_time */
	return ns_to_ktime(t << 10);
}

int __io_napi_add_id(struct io_ring_ctx *ctx, unsigned int napi_id)
{
	struct hlist_head *hash_list;
	struct io_napi_entry *e;

	/* Non-NAPI IDs can be rejected. */
	if (napi_id < MIN_NAPI_ID)
		return -EINVAL;

	hash_list = &ctx->napi_ht[hash_min(napi_id, HASH_BITS(ctx->napi_ht))];

	scoped_guard(rcu) {
		e = io_napi_hash_find(hash_list, napi_id);
		if (e) {
			WRITE_ONCE(e->timeout, jiffies + NAPI_TIMEOUT);
			return -EEXIST;
		}
	}

	e = kmalloc(sizeof(*e), GFP_NOWAIT);
	if (!e)
		return -ENOMEM;

	e->napi_id = napi_id;
	e->timeout = jiffies + NAPI_TIMEOUT;

	/*
	 * guard(spinlock) is not used to manually unlock it before calling
	 * kfree()
	 */
	spin_lock(&ctx->napi_lock);
	if (unlikely(io_napi_hash_find(hash_list, napi_id))) {
		spin_unlock(&ctx->napi_lock);
		kfree(e);
		return -EEXIST;
	}

	hlist_add_tail_rcu(&e->node, hash_list);
	list_add_tail_rcu(&e->list, &ctx->napi_list);
	spin_unlock(&ctx->napi_lock);
	return 0;
}

static void __io_napi_remove_stale(struct io_ring_ctx *ctx)
{
	struct io_napi_entry *e;

	guard(spinlock)(&ctx->napi_lock);
	/*
	 * list_for_each_entry_safe() is not required as long as:
	 * 1. list_del_rcu() does not reset the deleted node next pointer
	 * 2. kfree_rcu() delays the memory freeing until the next quiescent
	 *    state
	 */
	list_for_each_entry(e, &ctx->napi_list, list) {
		if (time_after(jiffies, READ_ONCE(e->timeout))) {
			list_del_rcu(&e->list);
			hash_del_rcu(&e->node);
			kfree_rcu(e, rcu);
		}
	}
}

static inline void io_napi_remove_stale(struct io_ring_ctx *ctx, bool is_stale)
{
	if (is_stale)
		__io_napi_remove_stale(ctx);
}

static inline bool io_napi_busy_loop_timeout(ktime_t start_time,
					     ktime_t bp)
{
	if (bp) {
		ktime_t end_time = ktime_add(start_time, bp);
		ktime_t now = net_to_ktime(busy_loop_current_time());

		return ktime_after(now, end_time);
	}

	return true;
}

static bool io_napi_busy_loop_should_end(void *data,
					 unsigned long start_time)
{
	struct io_wait_queue *iowq = data;

	if (signal_pending(current))
		return true;
	if (io_should_wake(iowq) || io_has_work(iowq->ctx))
		return true;
	if (io_napi_busy_loop_timeout(net_to_ktime(start_time),
				      iowq->napi_busy_poll_dt))
		return true;

	return false;
}

static bool __io_napi_do_busy_loop(struct io_ring_ctx *ctx,
				   void *loop_end_arg)
{
	struct io_napi_entry *e;
	bool (*loop_end)(void *, unsigned long) = NULL;
	bool is_stale = false;

	if (loop_end_arg)
		loop_end = io_napi_busy_loop_should_end;

	list_for_each_entry_rcu(e, &ctx->napi_list, list) {
		napi_busy_loop_rcu(e->napi_id, loop_end, loop_end_arg,
				   ctx->napi_prefer_busy_poll, BUSY_POLL_BUDGET);

		if (time_after(jiffies, READ_ONCE(e->timeout)))
			is_stale = true;
	}

	return is_stale;
}

static void io_napi_blocking_busy_loop(struct io_ring_ctx *ctx,
				       struct io_wait_queue *iowq)
{
	unsigned long start_time = busy_loop_current_time();
	void *loop_end_arg = NULL;
	bool is_stale = false;

	/* Singular lists use a different napi loop end check function and are
	 * only executed once.
	 */
	if (list_is_singular(&ctx->napi_list))
		loop_end_arg = iowq;

	scoped_guard(rcu) {
		do {
			is_stale = __io_napi_do_busy_loop(ctx, loop_end_arg);
		} while (!io_napi_busy_loop_should_end(iowq, start_time) &&
			 !loop_end_arg);
	}

	io_napi_remove_stale(ctx, is_stale);
}

/*
 * io_napi_init() - Init napi settings
 * @ctx: pointer to io-uring context structure
 *
 * Init napi settings in the io-uring context.
 */
void io_napi_init(struct io_ring_ctx *ctx)
{
	u64 sys_dt = READ_ONCE(sysctl_net_busy_poll) * NSEC_PER_USEC;

	INIT_LIST_HEAD(&ctx->napi_list);
	spin_lock_init(&ctx->napi_lock);
	ctx->napi_prefer_busy_poll = false;
	ctx->napi_busy_poll_dt = ns_to_ktime(sys_dt);
}

/*
 * io_napi_free() - Deallocate napi
 * @ctx: pointer to io-uring context structure
 *
 * Free the napi list and the hash table in the io-uring context.
 */
void io_napi_free(struct io_ring_ctx *ctx)
{
	struct io_napi_entry *e;

	guard(spinlock)(&ctx->napi_lock);
	list_for_each_entry(e, &ctx->napi_list, list) {
		hash_del_rcu(&e->node);
		kfree_rcu(e, rcu);
	}
	INIT_LIST_HEAD_RCU(&ctx->napi_list);
}

/*
 * io_napi_register() - Register napi with io-uring
 * @ctx: pointer to io-uring context structure
 * @arg: pointer to io_uring_napi structure
 *
 * Register napi in the io-uring context.
 */
int io_register_napi(struct io_ring_ctx *ctx, void __user *arg)
{
	const struct io_uring_napi curr = {
		.busy_poll_to 	  = ktime_to_us(ctx->napi_busy_poll_dt),
		.prefer_busy_poll = ctx->napi_prefer_busy_poll
	};
	struct io_uring_napi napi;

	if (ctx->flags & IORING_SETUP_IOPOLL)
		return -EINVAL;
	if (copy_from_user(&napi, arg, sizeof(napi)))
		return -EFAULT;
	if (napi.pad[0] || napi.pad[1] || napi.pad[2] || napi.resv)
		return -EINVAL;

	if (copy_to_user(arg, &curr, sizeof(curr)))
		return -EFAULT;

	WRITE_ONCE(ctx->napi_busy_poll_dt, napi.busy_poll_to * NSEC_PER_USEC);
	WRITE_ONCE(ctx->napi_prefer_busy_poll, !!napi.prefer_busy_poll);
	WRITE_ONCE(ctx->napi_enabled, true);
	return 0;
}

/*
 * io_napi_unregister() - Unregister napi with io-uring
 * @ctx: pointer to io-uring context structure
 * @arg: pointer to io_uring_napi structure
 *
 * Unregister napi. If arg has been specified copy the busy poll timeout and
 * prefer busy poll setting to the passed in structure.
 */
int io_unregister_napi(struct io_ring_ctx *ctx, void __user *arg)
{
	const struct io_uring_napi curr = {
		.busy_poll_to 	  = ktime_to_us(ctx->napi_busy_poll_dt),
		.prefer_busy_poll = ctx->napi_prefer_busy_poll
	};

	if (arg && copy_to_user(arg, &curr, sizeof(curr)))
		return -EFAULT;

	WRITE_ONCE(ctx->napi_busy_poll_dt, 0);
	WRITE_ONCE(ctx->napi_prefer_busy_poll, false);
	WRITE_ONCE(ctx->napi_enabled, false);
	return 0;
}

/*
 * __io_napi_busy_loop() - execute busy poll loop
 * @ctx: pointer to io-uring context structure
 * @iowq: pointer to io wait queue
 *
 * Execute the busy poll loop and merge the spliced off list.
 */
void __io_napi_busy_loop(struct io_ring_ctx *ctx, struct io_wait_queue *iowq)
{
	if (ctx->flags & IORING_SETUP_SQPOLL)
		return;

	iowq->napi_busy_poll_dt = READ_ONCE(ctx->napi_busy_poll_dt);
	if (iowq->timeout != KTIME_MAX) {
		ktime_t dt = ktime_sub(iowq->timeout, io_get_time(ctx));

		iowq->napi_busy_poll_dt = min_t(u64, iowq->napi_busy_poll_dt, dt);
	}

	iowq->napi_prefer_busy_poll = READ_ONCE(ctx->napi_prefer_busy_poll);
	io_napi_blocking_busy_loop(ctx, iowq);
}

/*
 * io_napi_sqpoll_busy_poll() - busy poll loop for sqpoll
 * @ctx: pointer to io-uring context structure
 *
 * Splice of the napi list and execute the napi busy poll loop.
 */
int io_napi_sqpoll_busy_poll(struct io_ring_ctx *ctx)
{
	bool is_stale = false;

	if (!READ_ONCE(ctx->napi_busy_poll_dt))
		return 0;
	if (list_empty_careful(&ctx->napi_list))
		return 0;

	scoped_guard(rcu) {
		is_stale = __io_napi_do_busy_loop(ctx, NULL);
	}

	io_napi_remove_stale(ctx, is_stale);
	return 1;
}

#endif