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Date: Mon, 25 Nov 2002 15:01:15 -0800 (PST)
From: Davide Libenzi <davidel@xmailserver.org>
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To: John Myers <jgmyers@netscape.com>
cc: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [rfc] new poll callback'd wake up hell ...
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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

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