kernel/include/kernel/interrupt.h

// Copyright 2018 The Fuchsia Authors
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT

#pragma once

#include <kernel/thread.h>

typedef struct int_handler_saved_state {
    bool old_preempt_pending;
} int_handler_saved_state_t;

// Start the main part of handling an interrupt in which preemption and
// blocking are disabled.  This must be matched by a later call to
// int_handler_finish().
static inline void int_handler_start(int_handler_saved_state_t* state) {
    arch_set_blocking_disallowed(true);
    thread_t* current_thread = get_current_thread();
    // Save the value of preempt_pending for restoring later.
    state->old_preempt_pending = current_thread->preempt_pending;
    // Clear preempt_pending so that we can later detect whether a
    // reschedule is made pending during the interrupt handler.
    current_thread->preempt_pending = false;
    thread_preempt_disable();
}

// Leave the main part of handling an interrupt, following a call to
// int_handler_start().
//
// This returns whether the caller should call thread_preempt().
static inline bool int_handler_finish(int_handler_saved_state_t* state) {
    thread_t* current_thread = get_current_thread();
    thread_preempt_reenable_no_resched();
    bool do_preempt = false;
    if (current_thread->preempt_pending) {
        // A preemption became pending during the interrupt handler.  If
        // preemption is now enabled, indicate that the caller should now
        // do the preemption.
        if (thread_preempt_disable_count() == 0) {
            do_preempt = true;
        }
    } else {
        // No preemption became pending during the interrupt handler.
        //
        // Restore the old value of preempt_pending.  This may be true if
        // resched_disable is non-zero.
        current_thread->preempt_pending = state->old_preempt_pending;
    }
    arch_set_blocking_disallowed(false);
    return do_preempt;
}