Re: [rfc] new poll callback'd wake up hell ...

[Davide Libenzi]

On Mon, 25 Nov 2002, John Myers wrote:

> Davide Libenzi wrote:
>
> >No, look at the code :
> >
> >
> Ok, I completely misread what you wrote.  I thought you were suggestiong
> a change to the locking behavior of wake_up() itself.

The problem with the wake_up() is its potential recursion when using the
callback'd version of the wait queue. We can have two scenarios ( given
'->' == CONTAINED-IN ) :

1)
epfd1 -> epfd2 -> ... ->epfdN with N huge

2)
epfd1 -> epfd2 -> ... -> epfd1

Now, when you call wake_up() without using any care you'll blow up the
stack. This should be adressed with the 0.58 version of the patch. Also, I
moved the :

        /* Add the current item to the list of active epoll hook for this file */
        spin_lock(&tfile->f_ep_lock);
        list_add_tail(&epi->fllink, &tfile->f_ep_links);
        spin_unlock(&tfile->f_ep_lock);

before inserting the item in the hash, so I don't need to increase the
usage count in ep_insert().

- Davide