__queue_work

static void __queue_work(int cpu, struct workqueue_struct *wq,
             struct work_struct *work)
{
    struct pool_workqueue *pwq;
    struct worker_pool *last_pool;
    struct list_head *worklist;
    unsigned int work_flags;
    unsigned int req_cpu = cpu;
 
    /*
     * While a work item is PENDING && off queue, a task trying to
     * steal the PENDING will busy-loop waiting for it to either get
     * queued or lose PENDING.  Grabbing PENDING and queueing should
     * happen with IRQ disabled.
     */
    lockdep_assert_irqs_disabled();
 
    debug_work_activate(work);
 
    /* if draining, only works from the same workqueue are allowed */
    if (unlikely(wq->flags & __WQ_DRAINING) &&
        WARN_ON_ONCE(!is_chained_work(wq)))
        return;
    rcu_read_lock();
retry:
    if (req_cpu == WORK_CPU_UNBOUND)
        cpu = wq_select_unbound_cpu(raw_smp_processor_id());
 
    /* pwq which will be used unless @work is executing elsewhere */
    if (!(wq->flags & WQ_UNBOUND))
        pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
    else
        pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));
 
    /*
     * If @work was previously on a different pool, it might still be
     * running there, in which case the work needs to be queued on that
     * pool to guarantee non-reentrancy.
     */
    last_pool = get_work_pool(work);
    if (last_pool && last_pool != pwq->pool) {
        struct worker *worker;
 
        spin_lock(&last_pool->lock);
 
        worker = find_worker_executing_work(last_pool, work);
 
        if (worker && worker->current_pwq->wq == wq) {
            pwq = worker->current_pwq;
        } else {
            /* meh... not running there, queue here */
            spin_unlock(&last_pool->lock);
            spin_lock(&pwq->pool->lock);
        }
    } else {
        spin_lock(&pwq->pool->lock);
    }
 
    /*
     * pwq is determined and locked.  For unbound pools, we could have
     * raced with pwq release and it could already be dead.  If its
     * refcnt is zero, repeat pwq selection.  Note that pwqs never die
     * without another pwq replacing it in the numa_pwq_tbl or while
     * work items are executing on it, so the retrying is guaranteed to
     * make forward-progress.
     */
    if (unlikely(!pwq->refcnt)) {
        if (wq->flags & WQ_UNBOUND) {
            spin_unlock(&pwq->pool->lock);
            cpu_relax();
            goto retry;
        }
        /* oops */
        WARN_ONCE(true, "workqueue: per-cpu pwq for %s on cpu%d has 0 refcnt",
              wq->name, cpu);
    }
 
    /* pwq determined, queue */
    trace_workqueue_queue_work(req_cpu, pwq, work);
 
    if (WARN_ON(!list_empty(&work->entry)))
        goto out;
 
    pwq->nr_in_flight[pwq->work_color]++;
    work_flags = work_color_to_flags(pwq->work_color);
 
    if (likely(pwq->nr_active < pwq->max_active)) {
        trace_workqueue_activate_work(work);
        pwq->nr_active++;
        worklist = &pwq->pool->worklist;
        if (list_empty(worklist))
            pwq->pool->watchdog_ts = jiffies;
    } else {
        work_flags |= WORK_STRUCT_DELAYED;
        worklist = &pwq->delayed_works;
    }
 
    insert_work(pwq, work, worklist, work_flags);
 
out:
    spin_unlock(&pwq->pool->lock);
    rcu_read_unlock();
}
函数源码
