Re: [take23 3/5] kevent: poll/select() notifications.

Davide Libenzi
2006-11-07T22:53:41Z

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).

- Davide