On Tue, Nov 08, 2005 at 07:24:29AM +0100, Oliver Neukum wrote:
> Am Dienstag, 8. November 2005 01:56 schrieb Herbert Xu:
> >
> > The kaweth driver does not delete the TX URB in kaweth_close().
> > As a result the TX URB may still be active in the USB subsystem.
> > If kaweth_open() is called quickly afterwards, the networking
> > layer could submit another packet before the existing TX URB has
> > completed.
>
> This begs the question how your first patch manages to avoid
> a race between hard_start_xmit() and disconnect()?
The existing usb_kill_urb calls in kaweth_disconnect() is racy:
CPU0 CPU1
kaweth_start_xmit
removed == 0
kaweth_disconnect
removed = 1
usb_kill_urb(tx_urb)
usb_submit_urb(tx_urb)
With my patches you have either:
CPU0 CPU1
dev_queue_xmit kaweth_disconnect -> unregister_netdev
dev_deactivate
spin_lock(queue_lock)
enqueue
qdisc_run
spin_unlock(queue_lock)
spin_lock(queue_lock)
qdisc = noop
qdisc_reset
spin_unlock(queue_lock)
dev_close
kaweth_close
usb_kill_urb(tx_urb)
Or
CPU0 CPU1
dev_queue_xmit kaweth_disconnect -> unregister_netdev
dev_deactivate
spin_lock(queue_lock)
qdisc = noop
qdisc_reset
spin_unlock(queue_lock)
dev_close
kaweth_close
usb_kill_urb(tx_urb)
spin_lock(queue_lock)
enqueue -> kfree_skb
qdisc_run
spin_unlock(queue_lock)
In either cases by the time dev_deactivate terminates, no further calls
to kaweth_start_xmit are possible. All calls made before its termination
will have terminated due to the spin_unlock_wait in dev_deactivate and
any tx_urb submitted will be taken care of by the usb_kill_urb in
kaweth_close.
Actually, there may be one unusual case where it could break. Namely when
the user uses a qdisc with no enqueue function then the queue_lock won't
be taken and the above analysis is no longer valid.
However, this would really a bug in dev_queue_xmit since it won't only
affect kaweth, but many other NIC drivers as well. So we should fix it
there (if this bug exists at all).
Thanks,
--
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <[EMAIL PROTECTED]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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