Epoll/ep_remove at master · grasslog/Epoll · GitHub

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static int ep_remove(struct eventpoll *ep, struct epitem *epi)
{
    unsigned long flags;
    struct file *file = epi->ffd.file;

    /*
     * Removes poll wait queue hooks. We _have_ to do this without holding
     * the "ep->lock" otherwise a deadlock might occur. This because of the
     * sequence of the lock acquisition. Here we do "ep->lock" then the wait
     * queue head lock when unregistering the wait queue. The wakeup callback
     * will run by holding the wait queue head lock and will call our callback
     * that will try to get "ep->lock".
     */
    ep_unregister_pollwait(ep, epi);

    /* Remove the current item from the list of epoll hooks */
    spin_lock(&file->f_lock);
    if (ep_is_linked(&epi->fllink))
        list_del_init(&epi->fllink);
    spin_unlock(&file->f_lock);

    rb_erase(&epi->rbn, &ep->rbr);

    spin_lock_irqsave(&ep->lock, flags);
    if (ep_is_linked(&epi->rdllink))
        list_del_init(&epi->rdllink);
    spin_unlock_irqrestore(&ep->lock, flags);

    /* At this point it is safe to free the eventpoll item */
    kmem_cache_free(epi_cache, epi);

    atomic_long_dec(&ep->user->epoll_watches);

    return 0;
}