Linux 内核 tasklet 机制和工作队列zz

struct cpu_workqueue_struct
{
    spinlock_t lock;
    
    struct list_head worklist;
    wait_queue_head_t more_work;
    struct work_struct *current_work;
    
    struct workqueue_struct *wq;
    struct task_struct *thread;
    
    int run_depth;        /* Detect run_workqueue() recursion depth */
} ____cacheline_aligned;

/*
 * The externally visible workqueue abstraction is an array of
 * per-CPU workqueues:
 */
struct workqueue_struct
{
    struct cpu_workqueue_struct *cpu_wq;
    struct list_head list;
    const char *name;
    int singlethread;
    int freezeable;        /* Freeze threads during suspend */
    int rt;
#ifdef CONFIG_LOCKDEP
    struct lockdep_map lockdep_map;
#endif
};

struct workqueue_struct *__create_workqueue_key(const char *name,
                                                int singlethread,
                                                int freezeable,
                                                int rt,
                                                struct lock_class_key *key,
                                                const char *lock_name)
{
    struct workqueue_struct *wq;
    struct cpu_workqueue_struct *cwq;
    int err = 0, cpu;wq = kzalloc(sizeof(*wq), GFP_KERNEL);
    if (!wq)
        return NULL;
    
    wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
    if (!wq->cpu_wq)
    {
        kfree(wq);
        return NULL;
    }
    
    wq->name = name;
    lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
    wq->singlethread = singlethread;
    wq->freezeable = freezeable;
    wq->rt = rt;
    INIT_LIST_HEAD(&wq->list);
    
    if (singlethread)
    {
        cwq = init_cpu_workqueue(wq, singlethread_cpu);
        err = create_workqueue_thread(cwq, singlethread_cpu);
        start_workqueue_thread(cwq, -1);
    }
    else
    {
        cpu_maps_update_begin();
        /*
         * We must place this wq on list even if the code below fails.
         * cpu_down(cpu) can remove cpu from cpu_populated_map before
         * destroy_workqueue() takes the lock, in that case we leak
         * cwq[cpu]->thread.
         */
        spin_lock(&workqueue_lock);
        list_add(&wq->list, &workqueues);
        spin_unlock(&workqueue_lock);
        /*
         * We must initialize cwqs for each possible cpu even if we
         * are going to call destroy_workqueue() finally. Otherwise
         * cpu_up() can hit the uninitialized cwq once we drop the
         * lock.
         */
        for_each_possible_cpu(cpu)
        {
            cwq = init_cpu_workqueue(wq, cpu);
            if (err || !cpu_online(cpu))
                continue;
            err = create_workqueue_thread(cwq, cpu);
            start_workqueue_thread(cwq, cpu);
        }
        cpu_maps_update_done();
    }
    
    if (err)
    {
        destroy_workqueue(wq);
        wq = NULL;
    }
    return wq;
}
EXPORT_SYMBOL_GPL(__create_workqueue_key);

/**
 * schedule_work - put work task in global workqueue
 * @work: job to be done
 *
 * This puts a job in the kernel-global workqueue.
 */
int schedule_work(struct work_struct *work)
{
    return queue_work(keventd_wq, work);
}
EXPORT_SYMBOL(schedule_work);

static int worker_thread(void *__cwq)
{
    struct cpu_workqueue_struct *cwq = __cwq;
    DEFINE_WAIT(wait);if (cwq->wq->freezeable)
        set_freezable();
    
    set_user_nice(current, -5);
    
    for (;;)
    {
        prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
        if (!freezing(current) &&
            !kthread_should_stop() &&
            list_empty(&cwq->worklist))
            schedule();
        finish_wait(&cwq->more_work, &wait);
        
        try_to_freeze();
        
        if (kthread_should_stop())
            break;
        
        run_workqueue(cwq);
    }
    
    return 0;
}

static void run_workqueue(struct cpu_workqueue_struct *cwq)
{
    spin_lock_irq(&cwq->lock);
    cwq->run_depth++;
    if (cwq->run_depth > 3)
    {
        /* morton gets to eat his hat */
        printk("%s: recursion depth exceeded: %dn",
               __func__, cwq->run_depth);
        dump_stack();
    }
    while (!list_empty(&cwq->worklist))
    {
        struct work_struct *work = list_entry(cwq->worklist.next,
                                              struct work_struct, entry);
        work_func_t f = work->func;
#ifdef CONFIG_LOCKDEP
        /*
         * It is permissible to free the struct work_struct
         * from inside the function that is called from it,
         * this we need to take into account for lockdep too.
         * To avoid bogus "held lock freed" warnings as well
         * as problems when looking into work->lockdep_map,
         * make a copy and use that here.
         */
        struct lockdep_map lockdep_map = work->lockdep_map;
#endifcwq->current_work = work;
        list_del_init(cwq->worklist.next);
        spin_unlock_irq(&cwq->lock);
        
        BUG_ON(get_wq_data(work) != cwq);
        work_clear_pending(work);
        lock_map_acquire(&cwq->wq->lockdep_map);
        lock_map_acquire(&lockdep_map);
        f(work);
        lock_map_release(&lockdep_map);
        lock_map_release(&cwq->wq->lockdep_map);
        
        if (unlikely(in_atomic() || lockdep_depth(current) > 0))
        {
            printk(KERN_ERR "BUG: workqueue leaked lock or atomic: "
                   "%s/0x%08x/%dn",
                   current->comm, preempt_count(),
                   task_pid_nr(current));
            printk(KERN_ERR "    last function: ");
            print_symbol("%sn", (unsigned long)f);
            debug_show_held_locks(current);
            dump_stack();
        }
        
        spin_lock_irq(&cwq->lock);
        cwq->current_work = NULL;
    }
    cwq->run_depth--;
    spin_unlock_irq(&cwq->lock);
}