closure.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Asynchronous refcounty things
 *
 * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
 * Copyright 2012 Google, Inc.
 */

#include <linux/closure.h>
#include <linux/debugfs.h>
#include <linux/export.h>
#include <linux/rcupdate.h>
#include <linux/seq_file.h>
#include <linux/sched/debug.h>

static inline void closure_put_after_sub_checks(int flags)
{
	int r = flags & CLOSURE_REMAINING_MASK;

	if (WARN(flags & CLOSURE_GUARD_MASK,
		 "closure has guard bits set: %x (%u)",
		 flags & CLOSURE_GUARD_MASK, (unsigned) __fls(r)))
		r &= ~CLOSURE_GUARD_MASK;

	WARN(!r && (flags & ~CLOSURE_DESTRUCTOR),
	     "closure ref hit 0 with incorrect flags set: %x (%u)",
	     flags & ~CLOSURE_DESTRUCTOR, (unsigned) __fls(flags));
}

static inline void closure_put_after_sub(struct closure *cl, int flags)
{
	closure_put_after_sub_checks(flags);

	if (!(flags & CLOSURE_REMAINING_MASK)) {
		smp_acquire__after_ctrl_dep();

		cl->closure_get_happened = false;

		if (cl->fn && !(flags & CLOSURE_DESTRUCTOR)) {
			atomic_set(&cl->remaining,
				   CLOSURE_REMAINING_INITIALIZER);
			closure_queue(cl);
		} else {
			struct closure *parent = cl->parent;
			closure_fn *destructor = cl->fn;

			closure_debug_destroy(cl);

			if (destructor)
				destructor(&cl->work);

			if (parent)
				closure_put(parent);
		}
	}
}

/* For clearing flags with the same atomic op as a put */
void closure_sub(struct closure *cl, int v)
{
	closure_put_after_sub(cl, atomic_sub_return_release(v, &cl->remaining));
}
EXPORT_SYMBOL(closure_sub);

/*
 * closure_put - decrement a closure's refcount
 */
void closure_put(struct closure *cl)
{
	closure_put_after_sub(cl, atomic_dec_return_release(&cl->remaining));
}
EXPORT_SYMBOL(closure_put);

/*
 * closure_wake_up - wake up all closures on a wait list, without memory barrier
 */
void __closure_wake_up(struct closure_waitlist *wait_list)
{
	struct llist_node *list;
	struct closure *cl, *t;
	struct llist_node *reverse = NULL;

	list = llist_del_all(&wait_list->list);

	/* We first reverse the list to preserve FIFO ordering and fairness */
	reverse = llist_reverse_order(list);

	/* Then do the wakeups */
	llist_for_each_entry_safe(cl, t, reverse, list) {
		closure_set_waiting(cl, 0);
		closure_sub(cl, CLOSURE_WAITING + 1);
	}
}
EXPORT_SYMBOL(__closure_wake_up);

/**
 * closure_wait - add a closure to a waitlist
 * @waitlist: will own a ref on @cl, which will be released when
 * closure_wake_up() is called on @waitlist.
 * @cl: closure pointer.
 *
 */
bool closure_wait(struct closure_waitlist *waitlist, struct closure *cl)
{
	if (atomic_read(&cl->remaining) & CLOSURE_WAITING)
		return false;

	cl->closure_get_happened = true;
	closure_set_waiting(cl, _RET_IP_);
	atomic_add(CLOSURE_WAITING + 1, &cl->remaining);
	llist_add(&cl->list, &waitlist->list);

	return true;
}
EXPORT_SYMBOL(closure_wait);

struct closure_syncer {
	struct task_struct	*task;
	int			done;
};

static CLOSURE_CALLBACK(closure_sync_fn)
{
	struct closure *cl = container_of(ws, struct closure, work);
	struct closure_syncer *s = cl->s;
	struct task_struct *p;

	rcu_read_lock();
	p = READ_ONCE(s->task);
	s->done = 1;
	wake_up_process(p);
	rcu_read_unlock();
}

void __sched __closure_sync(struct closure *cl)
{
	struct closure_syncer s = { .task = current };

	cl->s = &s;
	continue_at(cl, closure_sync_fn, NULL);

	while (1) {
		set_current_state(TASK_UNINTERRUPTIBLE);
		if (s.done)
			break;
		schedule();
	}

	__set_current_state(TASK_RUNNING);
}
EXPORT_SYMBOL(__closure_sync);

/*
 * closure_return_sync - finish running a closure, synchronously (i.e. waiting
 * for outstanding get()s to finish) and returning once closure refcount is 0.
 *
 * Unlike closure_sync() this doesn't reinit the ref to 1; subsequent
 * closure_get_not_zero() calls waill fail.
 */
void __sched closure_return_sync(struct closure *cl)
{
	struct closure_syncer s = { .task = current };

	cl->s = &s;
	set_closure_fn(cl, closure_sync_fn, NULL);

	unsigned flags = atomic_sub_return_release(1 + CLOSURE_RUNNING - CLOSURE_DESTRUCTOR,
						   &cl->remaining);

	closure_put_after_sub_checks(flags);

	if (unlikely(flags & CLOSURE_REMAINING_MASK)) {
		while (1) {
			set_current_state(TASK_UNINTERRUPTIBLE);
			if (s.done)
				break;
			schedule();
		}

		__set_current_state(TASK_RUNNING);
	}

	if (cl->parent)
		closure_put(cl->parent);
}
EXPORT_SYMBOL(closure_return_sync);

int __sched __closure_sync_timeout(struct closure *cl, unsigned long timeout)
{
	struct closure_syncer s = { .task = current };
	int ret = 0;

	cl->s = &s;
	continue_at(cl, closure_sync_fn, NULL);

	while (1) {
		set_current_state(TASK_UNINTERRUPTIBLE);
		if (s.done)
			break;
		if (!timeout) {
			/*
			 * Carefully undo the continue_at() - but only if it
			 * hasn't completed, i.e. the final closure_put() hasn't
			 * happened yet:
			 */
			unsigned old, new, v = atomic_read(&cl->remaining);
			do {
				old = v;
				if (!old || (old & CLOSURE_RUNNING))
					goto success;

				new = old + CLOSURE_REMAINING_INITIALIZER;
			} while ((v = atomic_cmpxchg(&cl->remaining, old, new)) != old);
			ret = -ETIME;
		}

		timeout = schedule_timeout(timeout);
	}
success:
	__set_current_state(TASK_RUNNING);
	return ret;
}
EXPORT_SYMBOL(__closure_sync_timeout);

#ifdef CONFIG_DEBUG_CLOSURES

static LIST_HEAD(closure_list);
static DEFINE_SPINLOCK(closure_list_lock);

void closure_debug_create(struct closure *cl)
{
	unsigned long flags;

	BUG_ON(cl->magic == CLOSURE_MAGIC_ALIVE);
	cl->magic = CLOSURE_MAGIC_ALIVE;

	spin_lock_irqsave(&closure_list_lock, flags);
	list_add(&cl->all, &closure_list);
	spin_unlock_irqrestore(&closure_list_lock, flags);
}
EXPORT_SYMBOL(closure_debug_create);

void closure_debug_destroy(struct closure *cl)
{
	unsigned long flags;

	if (cl->magic == CLOSURE_MAGIC_STACK)
		return;

	BUG_ON(cl->magic != CLOSURE_MAGIC_ALIVE);
	cl->magic = CLOSURE_MAGIC_DEAD;

	spin_lock_irqsave(&closure_list_lock, flags);
	list_del(&cl->all);
	spin_unlock_irqrestore(&closure_list_lock, flags);
}
EXPORT_SYMBOL(closure_debug_destroy);

static int debug_show(struct seq_file *f, void *data)
{
	struct closure *cl;

	spin_lock_irq(&closure_list_lock);

	list_for_each_entry(cl, &closure_list, all) {
		int r = atomic_read(&cl->remaining);

		seq_printf(f, "%p: %pS -> %pS p %p r %i ",
			   cl, (void *) cl->ip, cl->fn, cl->parent,
			   r & CLOSURE_REMAINING_MASK);

		seq_printf(f, "%s%s\n",
			   test_bit(WORK_STRUCT_PENDING_BIT,
				    work_data_bits(&cl->work)) ? "Q" : "",
			   r & CLOSURE_RUNNING	? "R" : "");

		if (r & CLOSURE_WAITING)
			seq_printf(f, " W %pS\n",
				   (void *) cl->waiting_on);

		seq_puts(f, "\n");
	}

	spin_unlock_irq(&closure_list_lock);
	return 0;
}

DEFINE_SHOW_ATTRIBUTE(debug);

static int __init closure_debug_init(void)
{
	debugfs_create_file("closures", 0400, NULL, NULL, &debug_fops);
	return 0;
}
late_initcall(closure_debug_init)

#endif