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

[Davide Libenzi]

On Mon, 25 Nov 2002, Davide Libenzi wrote:

> On Mon, 25 Nov 2002, Davide Libenzi wrote:
>
> > On Mon, 25 Nov 2002, John Myers wrote:
> >
> > > Davide Libenzi writes:
> > >  > 1) Move the wake_up() call done inside the poll callback outside the lock
> > >
> > > You can't.  You need to hold the lock over the callback or your callback
> > > could end up accessing a freed epitem.
> >
> > No, look at the code :
> >
> > http://www.xmailserver.org/linux-patches/sys_epoll-2.5.49-0.58.diff
> >
> > The function ep_collect_ready_items() increases the usage count under
> > lock. So the epintem is protected, and the file* cannot desappear because
> > of the read lock on epsem.
>
> Ops, I understood the f_op->poll() not the wake_up(). It can be solved in
> the same way. I'll do it now.

The only place where a protection is needed is inside ep_insert() and not
because of the wake_up() outsize the lock. Because of this :

        /* 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);

- Davide