On Thu, Aug 21, 2008 at 11:55:22AM +0000, Jarek Poplawski wrote:
quoted text
> 
> Sure, here is a scenario:
> 
> cpu1					cpu2
> rtnl_lock()
> qdisc_graft()
> // parent != NULL
> ->cops-graft()
> notify_and_destroy()			qdisc_run()
> 					spin_lock(root_lock)
> qdisc_destroy(old)			dequeue_skb()
> 					tbf_dequeue()
> 					qdisc_tree_decrease_qlen()	
> 					qdisc_lookup()
> //deleting from qdisc_sleeping->list	//walking qdisc_sleeping->list
> //under rtnl_lock() only		//under qdisc root_lock only
> list_del(qdisc->list)			list_for_each_entry(txq_root)

Good catch.  Longer term we should fix it so that it doesn't do
the silly lookup at run-time.  In fact we'll be getting rid of
requeue so there will be no need to do this in TBF at all.

However, for now please create a patch to put a pair of root locks
around the list_del in qdisc_destroy.

Thanks,
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