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    Subject[PATCH] 2.5.46: epoll ep_insert doesn't wake waiters if events exist

    The logic in fs/eventpoll.c:ep_insert() checks to see if events are
    already present when processing an EP_CTL_ADD operation, and, if any are,
    adds them to the list. It does not wake up any waiters, so, e.g., another
    thread waiting in epoll_wait() will not be awakened for these events. The
    fix is to have ep_insert() do wakeups, just as ep_poll_callback() does when
    it adds events.


    diff -ur linux-2.5.46.orig/fs/eventpoll.c linux-2.5.46/fs/eventpoll.c
    --- linux-2.5.46.orig/fs/eventpoll.c Thu Nov 7 14:31:21 2002
    +++ linux-2.5.46/fs/eventpoll.c Thu Nov 7 14:32:16 2002
    @@ -838,8 +838,13 @@
    list_add(&dpi->llink, ep_hash_entry(ep, ep_hash_index(ep, tfile)));

    /* If the file is already "ready" we drop it inside the ready list */
    - if ((revents & pfd->events) && !EP_IS_LINKED(&dpi->rdllink))
    + if ((revents & pfd->events) && !EP_IS_LINKED(&dpi->rdllink)) {
    list_add(&dpi->rdllink, &ep->rdllist);
    + if (waitqueue_active(&ep->wq))
    + wake_up(&ep->wq);
    + if (waitqueue_active(&ep->poll_wait))
    + wake_up(&ep->poll_wait);
    + }

    write_unlock_irqrestore(&ep->lock, flags);

    (See attached file: epoll-2.5.46-insert.patch)
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