af_packet: remove BUG statement in tpacket_destruct_skb

Here's a quote of the comment about the BUG macro from asm-generic/bug.h:

Don't use BUG() or BUG_ON() unless there's really no way out; one example might be detecting data structure corruption in the middle of an operation that can't be backed out of. If the (sub)system can somehow continue operating, perhaps with reduced functionality, it's probably not BUG-worthy.

If you're tempted to BUG(), think again: is completely giving up really the *only* solution? There are usually better options, where users don't need to reboot ASAP and can mostly shut down cleanly.

In our case, the status flag of a ring buffer slot is managed from both sides, the kernel space and the user space. This means that even though the kernel side might work as expected, the user space screws up and changes this flag right between the send(2) is triggered when the flag is changed to TP_STATUS_SENDING and a given skb is destructed after some time. Then, this will hit the BUG macro. As David suggested, the best solution is to simply remove this statement since it cannot be used for kernel side internal consistency checks. I've tested it and the system still behaves /stable/ in this case, so in accordance with the above comment, we should rather remove it.

---
 net/packet/af_packet.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

index ceaca7c..bbea24c 100644
@@ -1936,7 +1936,6 @@ static void tpacket_destruct_skb(struct sk_buff *skb)
 
 	if (likely(po->tx_ring.pg_vec)) {
 		ph = skb_shinfo(skb)->destructor_arg;
-		BUG_ON(__packet_get_status(po, ph) != TP_STATUS_SENDING);
 		BUG_ON(atomic_read(&po->tx_ring.pending) == 0);
 		atomic_dec(&po->tx_ring.pending);
 		__packet_set_status(po, ph, TP_STATUS_AVAILABLE);

From: Daniel Borkmann <[email protected]>
Date: Sat, 11 Aug 2012 10:48:54 +0200

Applied.