netdev - Re: [Linux-ATM-General] RX/close vcc race with solos/atmtcp/usbatm/he

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Message-ID: <1275926647.17903.5077.camel@macbook.infradead.org>
Date:	Mon, 07 Jun 2010 17:04:07 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	chas3@...rs.sourceforge.net
Cc:	linux-atm-general@...ts.sourceforge.net, netdev@...r.kernel.org
Subject: Re: [Linux-ATM-General] RX/close vcc race with
 solos/atmtcp/usbatm/he

On Mon, 2010-06-07 at 11:10 -0400, Chas Williams (CONTRACTOR) wrote:
> In message <1275920035.17903.4998.camel@...book.infradead.org>,David Woodhouse 
> writes:
> >On Mon, 2010-06-07 at 09:44 -0400, Chas Williams (CONTRACTOR) wrote:
> >> vcc's are really sockets, so you could just increase the refcount --
> >> sock_hold().
> >
> >There are rules about where we're allowed to call sock_hold(), and I
> >don't think our find_vcc() functions can be made to meet them.
> 
> if you are using find_vcc() then you should already have a lock on the
> hash table for the vccs.  you can safely increment the ref count at
> this point.

You can still hit the oops that way -- br2684_push() is setting
vcc->user_back to NULL before the final sock_put() anyway, and that's
what was causing the oops.

> >In that case I think we might as well stick with the RCU-like solution I
> >already implemented in the vcc close function -- which is just to wait
> >for the tasklet to complete, thus ensuring that it's no longer using the
> >defunct vcc.
> 
> the driver shouldnt close the vcc while the tasklet is running and
> using the vcc in question.  i guess the safest thing is to simply
> do as you are doing and not close while running the tasklet.

OK. :)

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation

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