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

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Date:	Mon, 07 Jun 2010 21:49:52 +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 12:37 -0400, Chas Williams (CONTRACTOR) wrote:
> i dont understand.  if you do a sock_hold() in find_vcc(), and then call
> vcc->push() you should be able to call vcc->push() and then sock_put(). 

Holding the reference doesn't stop the problem. The problem is

 vcc_release()
 --> vcc_destroy_socket()
   --> br2684_push(vcc, NULL)
         sets vcc->user_back = NULL
         (which it what causes the oops when try try to feed it any
          subsequent packets).

 Only _later_ does vcc_release() call sock_put().

It doesn't _matter_ that the tasklet is holding a reference on the
socket, because it's not the sk_free() which is causing the problem. 

Just making dev->ops->close() wait for the tasklet is perfectly
sufficient. That call happens from vcc_destroy_socket() before the call
to br2684_push(), and all is well.

-- 
dwmw2

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