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    SubjectRe: [take23 3/5] kevent: poll/select() notifications.
    On Tue, Nov 07, 2006 at 02:53:33PM -0800, Davide Libenzi (davidel@xmailserver.org) wrote:
    > On Tue, 7 Nov 2006, Evgeniy Polyakov wrote:
    >
    > > +static int kevent_poll_wait_callback(wait_queue_t *wait,
    > > + unsigned mode, int sync, void *key)
    > > +{
    > > + struct kevent_poll_wait_container *cont =
    > > + container_of(wait, struct kevent_poll_wait_container, wait);
    > > + struct kevent *k = cont->k;
    > > + struct file *file = k->st->origin;
    > > + u32 revents;
    > > +
    > > + revents = file->f_op->poll(file, NULL);
    > > +
    > > + kevent_storage_ready(k->st, NULL, revents);
    > > +
    > > + return 0;
    > > +}
    >
    > Are you sure you can safely call file->f_op->poll() from inside a callback
    > based wakeup? The low level driver may be calling the wakeup with one of
    > its locks held, and during the file->f_op->poll may be trying to acquire
    > the same lock. I remember there was a discussion about this, and assuming
    > the above not true, made epoll code more complex (and slower, since an
    > extra O(R) loop was needed to fetch events).

    Indeed, I have not paid too much attention to poll/select notifications in
    kevent actually. As far as I recall it should be called on behalf of process
    doing kevent_get_event(). I will check and fix if that is not correct.
    Thanks Davide.

    > - Davide
    >

    --
    Evgeniy Polyakov
    -
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