The "environmental" rules for authors of any new tc actions are:
  
  1) If you stealeth or borroweth any packet thou shalt be branching
  from the righteous path and thou shalt cloneth.
  
  For example if your action queues a packet to be processed later,
  or intentionally branches by redirecting a packet, then you need to
  clone the packet.
  
  2) If you munge any packet thou shalt call pskb_expand_head in the case
  someone else is referencing the skb. After that you "own" the skb.
  
  3) Dropping packets you don't own is a no-no. You simply return
  TC_ACT_SHOT to the caller and they will drop it.
  
  The "environmental" rules for callers of actions (qdiscs etc) are:
  
  *) Thou art responsible for freeing anything returned as being
  TC_ACT_SHOT/STOLEN/QUEUED. If none of TC_ACT_SHOT/STOLEN/QUEUED is
  returned, then all is great and you don't need to do anything.
  
  Post on netdev if something is unclear.