insert_wq_barrier

/**
 * insert_wq_barrier - insert a barrier work
 * @pwq: pwq to insert barrier into
 * @barr: wq_barrier to insert
 * @target: target work to attach @barr to
 * @worker: worker currently executing @target, NULL if @target is not executing
 *
 * @barr is linked to @target such that @barr is completed only after
 * @target finishes execution.  Please note that the ordering
 * guarantee is observed only with respect to @target and on the local
 * cpu.
 *
 * Currently, a queued barrier can't be canceled.  This is because
 * try_to_grab_pending() can't determine whether the work to be
 * grabbed is at the head of the queue and thus can't clear LINKED
 * flag of the previous work while there must be a valid next work
 * after a work with LINKED flag set.
 *
 * Note that when @worker is non-NULL, @target may be modified
 * underneath us, so we can't reliably determine pwq from @target.
 *
 * CONTEXT:
 * spin_lock_irq(pool->lock).
 */
static void insert_wq_barrier(struct pool_workqueue *pwq,
                  struct wq_barrier *barr,
                  struct work_struct *target, struct worker *worker)
{
    struct list_head *head;
    unsigned int linked = 0;
 
    /*
     * debugobject calls are safe here even with pool->lock locked
     * as we know for sure that this will not trigger any of the
     * checks and call back into the fixup functions where we
     * might deadlock.
     */
    INIT_WORK_ONSTACK(&barr->work, wq_barrier_func);
    __set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work));
 
    init_completion_map(&barr->done, &target->lockdep_map);
 
    barr->task = current;
 
    /*
     * If @target is currently being executed, schedule the
     * barrier to the worker; otherwise, put it after @target.
     */
    if (worker)
        head = worker->scheduled.next;
    else {
        unsigned long *bits = work_data_bits(target);
 
        head = target->entry.next;
        /* there can already be other linked works, inherit and set */
        linked = *bits & WORK_STRUCT_LINKED;
        __set_bit(WORK_STRUCT_LINKED_BIT, bits);
    }
 
    debug_work_activate(&barr->work);
    insert_work(pwq, &barr->work, head,
            work_color_to_flags(WORK_NO_COLOR) | linked);
}
函数源码
