linux-kernel - RE: epoll and closed file descriptors

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Message-ID: <024701ca372f$81412040$83c360c0$@com>
Date:	Wed, 16 Sep 2009 17:40:49 -0700
From:	"Gilad Benjamini" <gilad@...ornetworks.com>
To:	"'Davide Libenzi'" <davidel@...ilserver.org>
Cc:	"'Linux Kernel Mailing List'" <linux-kernel@...r.kernel.org>
Subject: RE: epoll and closed file descriptors

Davide wrote:
> On Wed, 16 Sep 2009, Gilad Benjamini wrote:
> 
> > I would, but epoll is preventing me from doing so.
> > Early in sys_epoll_ctl there are these lines
> >
> >   file = fget(epfd);
> >   if (!file)
> >     goto error_return;
> >
> > Leaving me in a kind of dead lock
> 
> The 'epfd' in there, is the _epoll fd_, which, if fget() fails, means
> you
> close it.
> You see likely failing the 'tfile = fget(fd)' (of course, you closed
> it),
> so if someone else keeps the socket open and you have no chance in
> telling
> it to drop it (really?), you need to remove the socket from the set
> before
> closing it.
> 
> 
> 
> - Davide

My bad. I meant to quote the line that you mentioned.
I agree that the right thing to do is to remove the fd from epoll before
closing it.
However, due to the way curl works, I cannot do that. Changing the curl code
doesn't seem trivial.

Regardless, I still don't see how the kernel got into this situation, and if
this situation is valid, why it doesn't bail out of it.


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