kernel/poll.c

/*
 * Copyright (c) 2017 Wind River Systems, Inc.
 *
 * SPDX-License-Identifier: Apache-2.0
 */

/**
 * @file
 *
 * @brief Kernel asynchronous event polling interface.
 *
 * This polling mechanism allows waiting on multiple events concurrently,
 * either events triggered directly, or from kernel objects or other kernel
 * constructs.
 */

#include <kernel.h>
#include <kernel_structs.h>
#include <kernel_internal.h>
#include <wait_q.h>
#include <ksched.h>
#include <syscall_handler.h>
#include <misc/slist.h>
#include <misc/dlist.h>
#include <misc/util.h>
#include <misc/__assert.h>
#include <stdbool.h>

/* Single subsystem lock.  Locking per-event would be better on highly
 * contended SMP systems, but the original locking scheme here is
 * subtle (it relies on releasing/reacquiring the lock in areas for
 * latency control and it's sometimes hard to see exactly what data is
 * "inside" a given critical section).  Do the synchronization port
 * later as an optimization.
 */
static struct k_spinlock lock;

void k_poll_event_init(struct k_poll_event *event, u32_t type,
		       int mode, void *obj)
{
	__ASSERT(mode == K_POLL_MODE_NOTIFY_ONLY,
		 "only NOTIFY_ONLY mode is supported\n");
	__ASSERT(type < (BIT(_POLL_NUM_TYPES)), "invalid type\n");
	__ASSERT(obj != NULL, "must provide an object\n");

	event->poller = NULL;
	/* event->tag is left uninitialized: the user will set it if needed */
	event->type = type;
	event->state = K_POLL_STATE_NOT_READY;
	event->mode = mode;
	event->unused = 0U;
	event->obj = obj;
}

/* must be called with interrupts locked */
static inline bool is_condition_met(struct k_poll_event *event, u32_t *state)
{
	switch (event->type) {
	case K_POLL_TYPE_SEM_AVAILABLE:
		if (k_sem_count_get(event->sem) > 0) {
			*state = K_POLL_STATE_SEM_AVAILABLE;
			return true;
		}
		break;
	case K_POLL_TYPE_DATA_AVAILABLE:
		if (!k_queue_is_empty(event->queue)) {
			*state = K_POLL_STATE_FIFO_DATA_AVAILABLE;
			return true;
		}
		break;
	case K_POLL_TYPE_SIGNAL:
		if (event->signal->signaled != 0U) {
			*state = K_POLL_STATE_SIGNALED;
			return true;
		}
		break;
	case K_POLL_TYPE_IGNORE:
		break;
	default:
		__ASSERT(false, "invalid event type (0x%x)\n", event->type);
		break;
	}

	return false;
}

static inline void add_event(sys_dlist_t *events, struct k_poll_event *event,
			     struct _poller *poller)
{
	struct k_poll_event *pending;

	pending = (struct k_poll_event *)sys_dlist_peek_tail(events);
	if ((pending == NULL) ||
		z_is_t1_higher_prio_than_t2(pending->poller->thread,
					    poller->thread)) {
		sys_dlist_append(events, &event->_node);
		return;
	}

	SYS_DLIST_FOR_EACH_CONTAINER(events, pending, _node) {
		if (z_is_t1_higher_prio_than_t2(poller->thread,
						pending->poller->thread)) {
			sys_dlist_insert(&pending->_node, &event->_node);
			return;
		}
	}

	sys_dlist_append(events, &event->_node);
}

/* must be called with interrupts locked */
static inline int register_event(struct k_poll_event *event,
				 struct _poller *poller)
{
	switch (event->type) {
	case K_POLL_TYPE_SEM_AVAILABLE:
		__ASSERT(event->sem != NULL, "invalid semaphore\n");
		add_event(&event->sem->poll_events, event, poller);
		break;
	case K_POLL_TYPE_DATA_AVAILABLE:
		__ASSERT(event->queue != NULL, "invalid queue\n");
		add_event(&event->queue->poll_events, event, poller);
		break;
	case K_POLL_TYPE_SIGNAL:
		__ASSERT(event->signal != NULL, "invalid poll signal\n");
		add_event(&event->signal->poll_events, event, poller);
		break;
	case K_POLL_TYPE_IGNORE:
		/* nothing to do */
		break;
	default:
		__ASSERT(false, "invalid event type\n");
		break;
	}

	event->poller = poller;

	return 0;
}

/* must be called with interrupts locked */
static inline void clear_event_registration(struct k_poll_event *event)
{
	bool remove = false;

	event->poller = NULL;

	switch (event->type) {
	case K_POLL_TYPE_SEM_AVAILABLE:
		__ASSERT(event->sem != NULL, "invalid semaphore\n");
		remove = true;
		break;
	case K_POLL_TYPE_DATA_AVAILABLE:
		__ASSERT(event->queue != NULL, "invalid queue\n");
		remove = true;
		break;
	case K_POLL_TYPE_SIGNAL:
		__ASSERT(event->signal != NULL, "invalid poll signal\n");
		remove = true;
		break;
	case K_POLL_TYPE_IGNORE:
		/* nothing to do */
		break;
	default:
		__ASSERT(false, "invalid event type\n");
		break;
	}
	if (remove && sys_dnode_is_linked(&event->_node)) {
		sys_dlist_remove(&event->_node);
	}
}

/* must be called with interrupts locked */
static inline void clear_event_registrations(struct k_poll_event *events,
					      int last_registered,
					      k_spinlock_key_t key)
{
	for (; last_registered >= 0; last_registered--) {
		clear_event_registration(&events[last_registered]);
		k_spin_unlock(&lock, key);
		key = k_spin_lock(&lock);
	}
}

static inline void set_event_ready(struct k_poll_event *event, u32_t state)
{
	event->poller = NULL;
	event->state |= state;
}

int z_impl_k_poll(struct k_poll_event *events, int num_events, s32_t timeout)
{
	__ASSERT(!z_is_in_isr(), "");
	__ASSERT(events != NULL, "NULL events\n");
	__ASSERT(num_events > 0, "zero events\n");

	int last_registered = -1, rc;
	k_spinlock_key_t key;

	struct _poller poller = { .thread = _current, .is_polling = true, };

	/* find events whose condition is already fulfilled */
	for (int ii = 0; ii < num_events; ii++) {
		u32_t state;

		key = k_spin_lock(&lock);
		if (is_condition_met(&events[ii], &state)) {
			set_event_ready(&events[ii], state);
			poller.is_polling = false;
		} else if (timeout != K_NO_WAIT && poller.is_polling) {
			rc = register_event(&events[ii], &poller);
			if (rc == 0) {
				++last_registered;
			} else {
				__ASSERT(false, "unexpected return code\n");
			}
		}
		k_spin_unlock(&lock, key);
	}

	key = k_spin_lock(&lock);

	/*
	 * If we're not polling anymore, it means that at least one event
	 * condition is met, either when looping through the events here or
	 * because one of the events registered has had its state changed.
	 */
	if (!poller.is_polling) {
		clear_event_registrations(events, last_registered, key);
		k_spin_unlock(&lock, key);
		return 0;
	}

	poller.is_polling = false;

	if (timeout == K_NO_WAIT) {
		k_spin_unlock(&lock, key);
		return -EAGAIN;
	}

	_wait_q_t wait_q = Z_WAIT_Q_INIT(&wait_q);

	int swap_rc = z_pend_curr(&lock, key, &wait_q, timeout);

	/*
	 * Clear all event registrations. If events happen while we're in this
	 * loop, and we already had one that triggered, that's OK: they will
	 * end up in the list of events that are ready; if we timed out, and
	 * events happen while we're in this loop, that is OK as well since
	 * we've already know the return code (-EAGAIN), and even if they are
	 * added to the list of events that occurred, the user has to check the
	 * return code first, which invalidates the whole list of event states.
	 */
	key = k_spin_lock(&lock);
	clear_event_registrations(events, last_registered, key);
	k_spin_unlock(&lock, key);

	return swap_rc;
}

#ifdef CONFIG_USERSPACE
Z_SYSCALL_HANDLER(k_poll, events, num_events, timeout)
{
	int ret;
	k_spinlock_key_t key;
	struct k_poll_event *events_copy = NULL;
	unsigned int bounds;

	/* Validate the events buffer and make a copy of it in an
	 * allocated kernel-side buffer.
	 */
	if (Z_SYSCALL_VERIFY(num_events > 0)) {
		ret = -EINVAL;
		goto out;
	}
	if (Z_SYSCALL_VERIFY_MSG(
		!__builtin_umul_overflow(num_events,
					sizeof(struct k_poll_event),
					&bounds),
					"num_events too large")) {
		ret = -EINVAL;
		goto out;
	}
	events_copy = z_thread_malloc(bounds);
	if (!events_copy) {
		ret = -ENOMEM;
		goto out;
	}

	key = k_spin_lock(&lock);
	if (Z_SYSCALL_MEMORY_WRITE(events, bounds)) {
		k_spin_unlock(&lock, key);
		goto oops_free;
	}
	(void)memcpy(events_copy, (void *)events, bounds);
	k_spin_unlock(&lock, key);

	/* Validate what's inside events_copy */
	for (int i = 0; i < num_events; i++) {
		struct k_poll_event *e = &events_copy[i];

		if (Z_SYSCALL_VERIFY(e->mode == K_POLL_MODE_NOTIFY_ONLY)) {
			ret = -EINVAL;
			goto out_free;
		}

		switch (e->type) {
		case K_POLL_TYPE_IGNORE:
			break;
		case K_POLL_TYPE_SIGNAL:
			Z_OOPS(Z_SYSCALL_OBJ(e->signal, K_OBJ_POLL_SIGNAL));
			break;
		case K_POLL_TYPE_SEM_AVAILABLE:
			Z_OOPS(Z_SYSCALL_OBJ(e->sem, K_OBJ_SEM));
			break;
		case K_POLL_TYPE_DATA_AVAILABLE:
			Z_OOPS(Z_SYSCALL_OBJ(e->queue, K_OBJ_QUEUE));
			break;
		default:
			ret = -EINVAL;
			goto out_free;
		}
	}

	ret = k_poll(events_copy, num_events, timeout);
	(void)memcpy((void *)events, events_copy, bounds);
out_free:
	k_free(events_copy);
out:
	return ret;
oops_free:
	k_free(events_copy);
	Z_OOPS(1);
}
#endif

/* must be called with interrupts locked */
static int signal_poll_event(struct k_poll_event *event, u32_t state)
{
	if (!event->poller) {
		goto ready_event;
	}

	struct k_thread *thread = event->poller->thread;

	__ASSERT(event->poller->thread != NULL,
		 "poller should have a thread\n");

	event->poller->is_polling = false;

	if (!z_is_thread_pending(thread)) {
		goto ready_event;
	}

	if (z_is_thread_timeout_expired(thread)) {
		return -EAGAIN;
	}

	z_unpend_thread(thread);
	z_set_thread_return_value(thread,
				 state == K_POLL_STATE_CANCELLED ? -EINTR : 0);

	if (!z_is_thread_ready(thread)) {
		goto ready_event;
	}

	z_ready_thread(thread);

ready_event:
	set_event_ready(event, state);
	return 0;
}

void z_handle_obj_poll_events(sys_dlist_t *events, u32_t state)
{
	struct k_poll_event *poll_event;

	poll_event = (struct k_poll_event *)sys_dlist_get(events);
	if (poll_event != NULL) {
		(void) signal_poll_event(poll_event, state);
	}
}

void z_impl_k_poll_signal_init(struct k_poll_signal *signal)
{
	sys_dlist_init(&signal->poll_events);
	signal->signaled = 0U;
	/* signal->result is left unitialized */
	z_object_init(signal);
}

#ifdef CONFIG_USERSPACE
Z_SYSCALL_HANDLER(k_poll_signal_init, signal)
{
	Z_OOPS(Z_SYSCALL_OBJ_INIT(signal, K_OBJ_POLL_SIGNAL));
	z_impl_k_poll_signal_init((struct k_poll_signal *)signal);
	return 0;
}
#endif

void z_impl_k_poll_signal_check(struct k_poll_signal *signal,
			       unsigned int *signaled, int *result)
{
	*signaled = signal->signaled;
	*result = signal->result;
}

#ifdef CONFIG_USERSPACE
Z_SYSCALL_HANDLER(k_poll_signal_check, signal, signaled, result)
{
	Z_OOPS(Z_SYSCALL_OBJ(signal, K_OBJ_POLL_SIGNAL));
	Z_OOPS(Z_SYSCALL_MEMORY_WRITE(signaled, sizeof(unsigned int)));
	Z_OOPS(Z_SYSCALL_MEMORY_WRITE(result, sizeof(int)));

	z_impl_k_poll_signal_check((struct k_poll_signal *)signal,
				  (unsigned int *)signaled, (int *)result);
	return 0;
}
#endif

int z_impl_k_poll_signal_raise(struct k_poll_signal *signal, int result)
{
	k_spinlock_key_t key = k_spin_lock(&lock);
	struct k_poll_event *poll_event;

	signal->result = result;
	signal->signaled = 1U;

	poll_event = (struct k_poll_event *)sys_dlist_get(&signal->poll_events);
	if (poll_event == NULL) {
		k_spin_unlock(&lock, key);
		return 0;
	}

	int rc = signal_poll_event(poll_event, K_POLL_STATE_SIGNALED);

	z_reschedule(&lock, key);
	return rc;
}

#ifdef CONFIG_USERSPACE
Z_SYSCALL_HANDLER(k_poll_signal_raise, signal, result)
{
	Z_OOPS(Z_SYSCALL_OBJ(signal, K_OBJ_POLL_SIGNAL));
	return z_impl_k_poll_signal_raise((struct k_poll_signal *)signal, result);
}
Z_SYSCALL_HANDLER1_SIMPLE_VOID(k_poll_signal_reset, K_OBJ_POLL_SIGNAL,
			       struct k_poll_signal *);
#endif