Re: [PATCH v2 3/3] pppoatm: protect against freeing of vcc

On Tue, Nov 27, 2012 at 06:02:29PM +0000, David Woodhouse wrote:

On Tue, 2012-11-27 at 18:39 +0100, Krzysztof Mazur wrote:

quoted

Yes, I missed that one - it's even worse, I introduced that bug 
in "[PATCH 1/7] atm: detach protocol before closing vcc". Before that
patch that scenario shouldn't happen because vcc was closed before
calling pppoatm_send(vcc, NULL) - the driver should provide appropriate
synchronization.

I think that we should just drop that patch. With later changes it's not
necessary - the pppoatm_send() can be safely called while closing vcc.

I'm not running with that patch. This bug exists for br2684 even before
it, and I think also for pppoatm.

In solos-pci at least, the ops->close() function doesn't flush all
pending skbs for this vcc before returning. So can be a tasklet
somewhere which has loaded the address of the vcc->pop function from one
of them, and is going to call it in some unspecified amount of time.

Should we make the device's ->close function wait for all TX and RX skbs
for this vcc to complete? 

Yes, the ->close() can sleep and after vcc is closed the ->pop() shouldn't be
called.


While reviewing your br2684 patch I also found that some ATM drivers does
not call ->pop() when ->send() fails, they should do:

	if (vcc->pop)
		vcc->pop(vcc, skb);
	else
		dev_kfree_skb(skb);

but some drivers just call dev_kfree_skb(skb).

I think that we should add atm_pop() function that does that and fix all
drivers.

Krzysiek