proc.c

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#include "proc_p.h"
#include "proc.h"

#include "cfg/cfg_proc.h"
#define LOG_LEVEL KERN_LOG_LEVEL
#define LOG_FORMAT KERN_LOG_FORMAT
#include <cfg/log.h>

#include "cfg/cfg_monitor.h"
#include <cfg/macros.h>    // ROUND_UP2
#include <cfg/module.h>
#include <cfg/depend.h>    // CONFIG_DEPEND()

#include <cpu/irq.h>
#include <cpu/types.h>
#include <cpu/attr.h>
#include <cpu/frame.h>

#if CONFIG_KERN_HEAP
    #include <struct/heap.h>
#endif

#include <string.h>           /* memset() */

#define PROC_SIZE_WORDS (ROUND_UP2(sizeof(Process), sizeof(cpu_stack_t)) / sizeof(cpu_stack_t))

/*
 * The scheduer tracks ready processes by enqueuing them in the
 * ready list.
 *
 * \note Access to the list must occur while interrupts are disabled.
 */
REGISTER List proc_ready_list;

/*
 * Holds a pointer to the TCB of the currently running process.
 *
 * \note User applications should use proc_current() to retrieve this value.
 */
REGISTER Process *current_process;

static struct Process main_process;

#if CONFIG_KERN_HEAP

static HEAP_DEFINE_BUF(heap_buf, CONFIG_KERN_HEAP_SIZE);
static Heap proc_heap;

/*
 * Keep track of zombie processes (processes that are exiting and need to
 * release some resources).
 *
 * \note Access to the list must occur while kernel preemption is disabled.
 */
static List zombie_list;

#endif /* CONFIG_KERN_HEAP */

/*
 * Check if the process context switch can be performed directly by the
 * architecture-dependent asm_switch_context() or if it must be delayed
 * because we're in the middle of an ISR.
 *
 * Return true if asm_switch_context() can be executed, false
 * otherwise.
 *
 * NOTE: if an architecture does not implement IRQ_RUNNING() this function
 * always returns true.
 */
#define CONTEXT_SWITCH_FROM_ISR()   (!IRQ_RUNNING())

/*
 * Save context of old process and switch to new process.
  */
static void proc_context_switch(Process *next, Process *prev)
{
    cpu_stack_t *dummy;

    if (UNLIKELY(next == prev))
        return;
    /*
     * If there is no old process, we save the old stack pointer into a
     * dummy variable that we ignore.  In fact, this happens only when the
     * old process has just exited.
     */
    asm_switch_context(&next->stack, prev ? &prev->stack : &dummy);
}

static void proc_initStruct(Process *proc)
{
    /* Avoid warning for unused argument. */
    (void)proc;

#if CONFIG_KERN_SIGNALS
    proc->sig_recv = 0;
    proc->sig_wait = 0;
#endif

#if CONFIG_KERN_HEAP
    proc->flags = 0;
#endif

#if CONFIG_KERN_PRI
    proc->link.pri = 0;
#endif
}

MOD_DEFINE(proc);

void proc_init(void)
{
    LIST_INIT(&proc_ready_list);

#if CONFIG_KERN_HEAP
    LIST_INIT(&zombie_list);
    heap_init(&proc_heap, heap_buf, sizeof(heap_buf));
#endif
    /*
     * We "promote" the current context into a real process. The only thing we have
     * to do is create a PCB and make it current. We don't need to setup the stack
     * pointer because it will be written the first time we switch to another process.
     */
    proc_initStruct(&main_process);
    current_process = &main_process;

#if CONFIG_KERN_MONITOR
    monitor_init();
    monitor_add(current_process, "main");
#endif
    MOD_INIT(proc);
}


#if CONFIG_KERN_HEAP

static void proc_freeZombies(void)
{
    Process *proc;

    while (1)
    {
        PROC_ATOMIC(proc = (Process *)list_remHead(&zombie_list));
        if (proc == NULL)
            return;

        if (proc->flags & PF_FREESTACK)
        {
            PROC_ATOMIC(heap_freemem(&proc_heap, proc->stack_base,
                proc->stack_size + PROC_SIZE_WORDS * sizeof(cpu_stack_t)));
        }
    }
}

static void proc_addZombie(Process *proc)
{
    Node *node;
#if CONFIG_KERN_PREEMPT
    ASSERT(!proc_preemptAllowed());
#endif

#if CONFIG_KERN_PRI
    node = &(proc)->link.link;
#else
    node = &(proc)->link;
#endif
    LIST_ASSERT_VALID(&zombie_list);
    ADDTAIL(&zombie_list, node);
}

#endif /* CONFIG_KERN_HEAP */

struct Process *proc_new_with_name(UNUSED_ARG(const char *, name), void (*entry)(void), iptr_t data, size_t stack_size, cpu_stack_t *stack_base)
{
    Process *proc;
    LOG_INFO("name=%s", name);
#if CONFIG_KERN_HEAP
    bool free_stack = false;

    /*
     * Free up resources of a zombie process.
     *
     * We're implementing a kind of lazy garbage collector here for
     * efficiency reasons: we can avoid to introduce overhead into another
     * kernel task dedicated to free up resources (e.g., idle) and we're
     * not introducing any overhead into the scheduler after a context
     * switch (that would be *very* bad, because the scheduler runs with
     * IRQ disabled).
     *
     * In this way we are able to release the memory of the zombie tasks
     * without disabling IRQs and without introducing any significant
     * overhead in any other kernel task.
     */
    proc_freeZombies();

    /* Did the caller provide a stack for us? */
    if (!stack_base)
    {
        /* Did the caller specify the desired stack size? */
        if (!stack_size)
            stack_size = KERN_MINSTACKSIZE;

        /* Allocate stack dinamically */
        PROC_ATOMIC(stack_base =
            (cpu_stack_t *)heap_allocmem(&proc_heap, stack_size));
        if (stack_base == NULL)
            return NULL;

        free_stack = true;
    }

#else // CONFIG_KERN_HEAP

    /* Stack must have been provided by the user */
    ASSERT_VALID_PTR(stack_base);
    ASSERT(stack_size);

#endif // CONFIG_KERN_HEAP

#if CONFIG_KERN_MONITOR
    /*
     * Fill-in the stack with a special marker to help debugging.
     * On 64bit platforms, CONFIG_KERN_STACKFILLCODE is larger
     * than an int, so the (int) cast is required to silence the
     * warning for truncating its size.
     */
    memset(stack_base, (int)CONFIG_KERN_STACKFILLCODE, stack_size);
#endif

    /* Initialize the process control block */
    if (CPU_STACK_GROWS_UPWARD)
    {
        proc = (Process *)stack_base;
        proc->stack = stack_base + PROC_SIZE_WORDS;
        // On some architecture stack should be aligned, so we do it.
        proc->stack = (cpu_stack_t *)((uintptr_t)proc->stack + (sizeof(cpu_aligned_stack_t) - ((uintptr_t)proc->stack % sizeof(cpu_aligned_stack_t))));
        if (CPU_SP_ON_EMPTY_SLOT)
            proc->stack++;
    }
    else
    {
        proc = (Process *)(stack_base + stack_size / sizeof(cpu_stack_t) - PROC_SIZE_WORDS);
        // On some architecture stack should be aligned, so we do it.
        proc->stack = (cpu_stack_t *)((uintptr_t)proc - ((uintptr_t)proc % sizeof(cpu_aligned_stack_t)));
        if (CPU_SP_ON_EMPTY_SLOT)
            proc->stack--;
    }
    /* Ensure stack is aligned */
    ASSERT((uintptr_t)proc->stack % sizeof(cpu_aligned_stack_t) == 0);

    stack_size -= PROC_SIZE_WORDS * sizeof(cpu_stack_t);
    proc_initStruct(proc);
    proc->user_data = data;

#if CONFIG_KERN_HEAP | CONFIG_KERN_MONITOR
    proc->stack_base = stack_base;
    proc->stack_size = stack_size;
    #if CONFIG_KERN_HEAP
    if (free_stack)
        proc->flags |= PF_FREESTACK;
    #endif
#endif
    proc->user_entry = entry;
    CPU_CREATE_NEW_STACK(proc->stack);

#if CONFIG_KERN_MONITOR
    monitor_add(proc, name);
#endif

    /* Add to ready list */
    ATOMIC(SCHED_ENQUEUE(proc));

    return proc;
}

const char *proc_name(struct Process *proc)
{
#if CONFIG_KERN_MONITOR
    return proc ? proc->monitor.name : "<NULL>";
#else
    (void)proc;
    return "---";
#endif
}

const char *proc_currentName(void)
{
    return proc_name(proc_current());
}

void proc_rename(struct Process *proc, const char *name)
{
#if CONFIG_KERN_MONITOR
    monitor_rename(proc, name);
#else
    (void)proc; (void)name;
#endif
}


#if CONFIG_KERN_PRI

void proc_setPri(struct Process *proc, int pri)
{
    if (proc->link.pri == pri)
        return;

    proc->link.pri = pri;

    if (proc != current_process)
        ATOMIC(sched_reenqueue(proc));
}
#endif // CONFIG_KERN_PRI

INLINE void proc_run(void)
{
    void (*entry)(void) = current_process->user_entry;

    LOG_INFO("New process starting at %p", entry);
    entry();
}

void proc_entry(void)
{
    /*
     * Return from a context switch assumes interrupts are disabled, so
     * we need to explicitly re-enable them as soon as possible.
     */
    IRQ_ENABLE;
    /* Call the actual process's entry point */
    proc_run();
    proc_exit();
}

void proc_exit(void)
{
    LOG_INFO("%p:%s", current_process, proc_currentName());

#if CONFIG_KERN_MONITOR
    monitor_remove(current_process);
#endif

    proc_forbid();
#if CONFIG_KERN_HEAP
    /*
     * Set the task as zombie, its resources will be freed in proc_new() in
     * a lazy way, when another process will be created.
     */
    proc_addZombie(current_process);
#endif
    current_process = NULL;
    proc_permit();

    proc_switch();

    /* never reached */
    ASSERT(0);
}

static void proc_schedule(void)
{
    Process *old_process = current_process;

    IRQ_ASSERT_DISABLED();

    /* Poll on the ready queue for the first ready process */
    LIST_ASSERT_VALID(&proc_ready_list);
    while (!(current_process = (struct Process *)list_remHead(&proc_ready_list)))
    {
        /*
         * Make sure we physically reenable interrupts here, no matter what
         * the current task status is. This is important because if we
         * are idle-spinning, we must allow interrupts, otherwise no
         * process will ever wake up.
         *
         * During idle-spinning, an interrupt can occur and it may
         * modify \p proc_ready_list. To ensure that compiler reload this
         * variable every while cycle we call CPU_MEMORY_BARRIER.
         * The memory barrier ensure that all variables used in this context
         * are reloaded.
         * \todo If there was a way to write sig_wait() so that it does not
         * disable interrupts while waiting, there would not be any
         * reason to do this.
         */
        IRQ_ENABLE;
        CPU_IDLE;
        MEMORY_BARRIER;
        IRQ_DISABLE;
    }
    if (CONTEXT_SWITCH_FROM_ISR())
        proc_context_switch(current_process, old_process);
    /* This RET resumes the execution on the new process */
    LOG_INFO("resuming %p:%s\n", current_process, proc_currentName());
}

#if CONFIG_KERN_PREEMPT
/* Global preemption nesting counter */
cpu_atomic_t preempt_count;

/*
 * The time sharing interval: when a process is scheduled on a CPU it gets an
 * amount of CONFIG_KERN_QUANTUM clock ticks. When these ticks expires and
 * preemption is enabled a new process is selected to run.
 */
int _proc_quantum;

bool proc_needPreempt(void)
{
    if (UNLIKELY(current_process == NULL))
        return false;
    if (!proc_preemptAllowed())
        return false;
    if (LIST_EMPTY(&proc_ready_list))
        return false;
    return preempt_quantum() ? prio_next() > prio_curr() :
            prio_next() >= prio_curr();
}

void proc_preempt(void)
{
    IRQ_ASSERT_DISABLED();
    ASSERT(current_process);

    /* Perform the kernel preemption */
    LOG_INFO("preempting %p:%s\n", current_process, proc_currentName());
    /* We are inside a IRQ context, so ATOMIC is not needed here */
    SCHED_ENQUEUE(current_process);
    preempt_reset_quantum();
    proc_schedule();
}
#endif /* CONFIG_KERN_PREEMPT */

/* Immediately switch to a particular process */
static void proc_switchTo(Process *proc)
{
    Process *old_process = current_process;

    SCHED_ENQUEUE(current_process);
    preempt_reset_quantum();
    current_process = proc;
    proc_context_switch(current_process, old_process);
}

void proc_switch(void)
{
    ASSERT(proc_preemptAllowed());
    ATOMIC(
        preempt_reset_quantum();
        proc_schedule();
    );
}

void proc_wakeup(Process *proc)
{
    ASSERT(proc_preemptAllowed());
    ASSERT(current_process);
    IRQ_ASSERT_DISABLED();

    if (prio_proc(proc) >= prio_curr())
        proc_switchTo(proc);
    else
        SCHED_ENQUEUE_HEAD(proc);
}

void proc_yield(void)
{
    Process *proc;

    /*
     * Voluntary preemption while preemption is disabled is considered
     * illegal, as not very useful in practice.
     *
     * ASSERT if it happens.
     */
    ASSERT(proc_preemptAllowed());
    IRQ_ASSERT_ENABLED();

    IRQ_DISABLE;
    proc = (struct Process *)list_remHead(&proc_ready_list);
    if (proc)
        proc_switchTo(proc);
    IRQ_ENABLE;
}